NETWORKED FACILITIES MANAGEMENT SYSTEM

Abstract: A networked system having a wide variety of applications and particularly applicable to facilities management systems has multiple levels of software in processing nodes. The levels include a "features" processing level which communicates requests for data to a software object level containing databases of processes and attributes and database managers. The database managers in the software object level operate to provide data to the high level features in the same format. The software object level communicates with a hardware object level which also contains databases and database managers to mask differences between operational hardware units. By categorizing operational units by type, additional units of a known type can be added with only low level hardware object database changes. Adding units of a new type is facilitated by software changes confined to the lower level hardware and software objects, avoiding software changes at high level features. Individual software objects are tailored for typical types of inputs and output devices encountered by facilities management systems. Universal drive circuitry also provides applicability to a broad range of devices.

Description: NETWORKED FACILITIES MANAGEMENT SYSTEM Background of the Invention 1. Field of the Invention The invention relates to automated processing systems which can operate independently or be interconnected to form a network. In particular the invention can be used in a Facilities Management Systems (FMS) , although it is not limited to such systems. 2. Related Art State of the art automated systems operating under processor control pass data to and from processors, operational units such as sensors and other physical parameter monitoring units, and other data acquisition and control instruments implemented in hardware. Facilities Management Systems (FMS) performing automated industrial and environmental control are among such contemporary systems. Since there is no uniformity among various types of data acquisition and control instruments, automated systems must be compatible with a multitude of non- standard operational units. To achieve compatibility, such systems have often relied on software tailored to specific interface requirements. This requires numerous compromises in software design. In addition, when new operational units are added, or existing operational units are changed, it often becomes necessary to rewrite one or more entire software package. This is because requirements of new operational units are often incompatible with software written for earlier units. Since the interfaces among various portions of the software and between operational units and the processor are an integral part of the software, the entire software package must be rewritten. One approach to reducing the extent of software affected by changes in operational units is the use of logical point information nodes. This is a modular approach which seeks to isolate high level software features from operational unit specific characteristics. However, this approach remains relatively dependent on the physical or logical location of operational units and on their individual characteristics. While some level of isolation of high level software features could be achieved by such a modular approach, it is still necessary to write operational unit specific software to accommodate inputs and outputs. Thus, using known technology, it has not been possible to provide software which would be relatively unaffected by the differences in operational unit hardware. As a result, it has also not been possible to produce software which need not be extensively modified when new operational units are added or existing data acquisition units are substantially changed. A further limitation of the related art, especially in systems employing data acquisition and other remotely controlled hardware, is the limited data constructs available. Data acquisition and other remotely controlled hardware typically provide and require specifically formatted data and often do not allow convenient access to desired portions of the data. As a result, in current systems it is sometimes necessary to duplicate data to be used for different purposes or again access data previously obtained. Similarly, it is sometimes difficult in such systems to access intermediate data developed by a processing apparatus rather than data gathered directly by a data acquisition device. Automated systems, including those used for facilities management, can operate using centralized or distributed processing techniques. As a result, data at a host node can be accessed for processing at another node (a referencing node) connected to the host node over a network. In distributed real time processing systems, processor nodes operating relatively independently communicate over one or more data buses to exchange information. In order for a referencing node to access a data element within the data base of a host node, a convention must be established whereby the referencing node can identify the host node whose data base contains the required data element and the specific location of the data element within the host node. Such a convention should avoid relying on a central node to translate a data access request to the appropriate host node address or address within the host node. This is because a failure of the central node performing this function would prevent operation of the entire system. It would also be unacceptable to search an entire real time network or even the data base of one node for a particular data element. This is because the time consumed by such a search would be excessive. Thus, a direct access mechanism to obtain the required data from within the host node is needed. Moreover, the data base at each node of the distributed system should be independent of data bases at other nodes of the system. It should not be necessary to synchronize the nodes by downloading new data into referencing nodes each time a host data base is changed. Data that was available previously from a host node should, if still present, be available to referencing nodes regardless of how the host node data base addresses are changed. Moreover, the data should still be available to the referencing node, even when the data element moves from one node to another. Conventional techniques for referencing data between nodes on such distributed real time systems cannot meet all of the above requirements simultaneously. One known approach is the use of hard memory addresses. A referencing node maintains in its data base a fixed memory address of the data within the host data base. The address is normally bound to a named element of data when the referencing data base is generated, usually in an off-line generation device. The results are then downloaded to the on-line nodes to allow direct access to the data within the host node. While this technique provides quick access to data and does not require a central node to translate addresses, there is no adaptability to changes in the host node data base. Host node data base changes that result in address changes within the node cause fixed memory addresses associated with the data elements in the referencing nodes to become obsolete. The same problem arises when a data element moves from one node to another. As a result, all the referencing nodes must be re-synchronized to the new addresses of the data elements. Especially in large systems, this is a time consuming task which causes the referencing nodes to be taken off line until the update is complete. In a facilities management system, (FMS) the referencing nodes perform industrial and environmental control functions which often can no longer be maintained when the node is off line. A second technique uses a "soft" address or record number to locate a data element within the host node. Using this technique, the relative position within a logical data base structure or a unique identifying number is assigned to a data element. As with the hard memory address technique, high speed and reliable access to the data is achieved. However, if the host node data base changes so that the relative position of the element in the data base is now different, the reference nodes are again obsolete and new information must be downloaded to the referencing devices. An additional problem occurs when attempting to assign a unique identifying number to a data item. Without further processing, it is impossible to guarantee that the same identifying number is not used by more than one host in the distributed system. This would create an intolerable conflict on the network. Finally, after referencing nodes are updated, it would not be possible to download an old data base to the host node since this would now invalidate the information in the referencing nodes. A third conventional approach involves assigning a name to each data element in the system. The names are stored in a central node which is used to locate the data. While this allows increased flexibility because data elements can move at will, this central node containing the mapping of names to physical locations becomes a reliability problem. This is because a failure in the central node would eliminate all communication on the network. The fourth conventional approach also assigns a name to each data element but avoids the central lookup node by searching the network each time the reference is made. However, in most systems, searching an entire network for a data element each time it is requested would result in an intolerable data communication and processing burden. Networked systems with a plurality of nodes further require synchronizing time and global data for consistent operation. This is especially true in a facilities management system in which scheduled activities, such as temperature control of areas of a building, may operate routinely based on time of day and other variables. Thus, one of the nodes on the system must accurately track time and coordinate the time information among the other nodes. However, current systems employing master nodes risk loosing time coordination should the master node fail. As additional nodes are brought onto a networked system, it also becomes necessary to synchronize the data base of each new node with the most current data base of global variables. Traditional systems which employ a master node to perform these functions also risk reliability problems in this area should the master node fail. Similarly, operational units communicating with individual nodes or intermediate processors between the nodes and the operational units can be connected to the nodes using data bus networks or similar structures. For consistency, it is necessary that operational and processing units connected to the individual nodes receive the most current values of system variables. Networked systems under master node control introduce similar reliability risks at this level. In automatic processing systems, high level software features and routines may be triggered by events occurring in other processors at the same level or in lower level processors controlled by one of the nodes on the system. However, data base changes occurring from down-loading new information into one of the nodes could result in errors in such event triggering. Current systems which do not track these event triggering synchronization problems are unable to guarantee that important software functions will be performed after downloading new information into one of the nodes. Similarly, reports of results produced by processes performed in the system, or of commands issued by the system, must be routed to appropriate display or storage devices. Current systems which do not accommodate changing the locations of such devices are severely restricted in dynamic environments. Similarly, current systems which do not synchronize changes in the location data of such devices downloaded into the nodes cannot guarantee that reports or messages will arrive at the correct device. Indeed, in some systems, messages which cannot be routed are discarded. This is a potentially serious limitation to applying such designs to facilities management systems. Often, especially in facilities management systems, displays and reports include standardized summarizes of system data. In a typical approach to generating standard summaries, a processor retrieves individual records, either in response to a command or as part of routine polling of devices for data awaiting transmission. The processor must then test the retrieved data to determine if incorporation into the data summary being assembled is appropriate. Such dedicated summary report generation tests occupy the processors and intensify data communications, resulting in reducing achievable processing speeds. In some cases, it is desirable to obtain reports by routing messages to devices which were not part of the network when configured. For example, ease of maintenance may be enhanced by allowing connection of a personal computer (PC) to an unoccupied port on a network node. It may also be desirable to provide other non-configured devices, such as printers, access to the nodes on the network. Traditional systems restrict the use of such non-configured devices, since there is no way to communicate with a device whose presence has not previously been made known to the network, for example, by assignment and storage of an address. As previously noted, networked systems have at least 2 nodes with components for performing processing functions appropriate to the system and communicating with each other over communication links. In a facilities management system (FMS) such nodes can contain processors, A/D and D/A converters and other equipment interface circuits to obtain sensor data required for processes implemented in the node and to issue equipment commands. The communication links include various communication media facilitating communication among nodes on the same bus, subnet or network or between nodes on different networks over gateways. Nodes are configured on a system when they are defined in one or more storage devices as members of a network. Node configuration may occur by storing data defining a path to the node. Thus, the system has knowledge of the node's existence. Depending on the system, storage of configuration information may be centralized or distributed. Such configuration information may include data indicating the type of node, its location on the system, and other information defining a path to the node. A number of techniques for communicating among nodes interconnected on a networked system currently exist. In broadcast communications methods, all nodes on a network receive a broadcast message or pass the message sequentially from one node to the next. Inefficient communications result from each node's handling of the broadcast message. Thus, other routing strategies have been developed to improve network efficiency. Routing strategies may be adaptive or non- adaptive and systems may contain elements of both strategies. Non-adaptive routing strategies route messages independently of measurements or estimates of current traffic or topology. These may include flooding or broadcast, selective flooding, and static routing. One such non-adaptive routing strategy involves building a graph of communication paths from every node to every other node within the network and between networks interconnected by a gateway. Graph analysis techniques for determining the shortest path between pairs of nodes are employed and this information is then programmed into a static routing table. In one such routing table, each node stores partial path data identifying the next intermediate destination for a message ultimately targeted for a final destination node. Since each node has a static routing table which is defined at the time of node configuration, it is inconvenient to alter the routing table to facilitate communications by temporary or extraneous nodes which are not normally part of the network. This is because only nodes listed in the routing table are available for use in the data communications path. Dynamic or adaptive routing strategies route messages over communications links in response to message traffic and topology. Adaptive strategies include centralized, isolated or decentralized, and dynamic routing. Centralized routing strategies have a central node monitoring the number and length of messages transmitted over communications links and dynamically issuing routing strategies based on message traffic patterns. This is usually accomplished by updating and changing routing tables in response to the changing traffic patterns. Decentralized strategies distribute partial routing tables among the nodes. For example, when a message is routed to an intermediate node along a path to its final destination, the intermediate node examines the traffic pattern among alternative remaining paths to the destination node and dynamically selects one of the several alternatives according to certain measures of efficiency. Thus, adaptive strategies provide for reconfiguring routing tables in response to changed conditions, including the addition of new devices. However, in many cases it is not possible to incorporate non- configured devices. Even where this is possible, the temporary incorporation of a previously non- configured device often does not justify the added processing required for dynamically adjusting routing tables. Such processing increases message transmission time and reduces overall system efficiency. Regardless of the routing strategy employed by various parts of the system, in certain applications, such as maintenance, diagnostics, and administrative functions, it is desirable to allow data communications between a node on one of the communications links in the system and a temporary node or processing device. This is particularly true in automated networked control systems. Such systems often have need for emergency maintenance and diagnostic activities and for temporary load analysis. Present techniques are cumbersome because these require temporarily disabling at least portions of the network while a new node is configured onto the network. Configuring new nodes on a network is difficult since new data communication path strategies must be worked out. Moreover, developing temporary data path strategies could result in inefficient communication strategies between the temporary or non-configured device and the nodes configured on the network. In networked automated processing or computer systems multiple processors requiring access to the same data may exist. Often this data is acquired by one of the processors which communicates with a particular sensor. Other processors requiring the same data communicate with the processor containing the data, either directly or through an intermediary, over a data bus. Using currently existing methods, a processor requiring sensor data not available through its own sensors, communicates over the data bus to signal the processor interfacing with the sensor that data is required. In response, the processor connected to the sensor polls the sensor and retrieves the data. It then transmits this data to the requesting processor for use in the remote processing routine. In another known arrangement, the remote processors signal a master node that data is required from a sensor controlled by a different processor. The master node then signals the sensor controlling processor which then retrieves the data and transmits it to the master node. The master node then provides the data to the requesting remote processor. Thus, each time a processor requires data from a sensor, the sensor controlling processor must access the sensor and transmit the information either to the requesting processor or the master node. If numerous processors request frequent access to sensor information, the data bus connecting the remote processors to each other and/or to a master node quickly becomes bogged down with message traffic. In another known method, slave sensors connected on a bus to a master sensor are set up with a filtering increment. When a filtering increment is used, the slave processor controlling the sensor defines a certain "delta" value that the sensor must change before the slave will report the new value to the master. The master keeps a copy of the data as the slave transmits it. When a filtering increment is employed, the slave processor determines how often data is sent to the master. Thus, even if the master processor has no requirement for updated sensor information, the slave processor signals the master that the information is to be transmitted. If the sensor parameter is one which changes frequently, the slave processor may inordinately occupy the data bus with unnecessary updates of information to the master processor. In another known method, the master regularly polls each processor for sensor updates. This also results in excessive message traffic on the interconnecting bus, since data is transmitted automatically, even when updates are not needed. In addition, polling systems risk missing important transient data transitions which might occur in a sensor while the master is polling another sensor. In each of the above cases, unnecessary message traffic on the data bus tends to create bottlenecks and reduces the ability of the data bus to respond quickly to higher priority message traffic. Another factor often not considered in modern automated processing and data communication systems is the reliability or integrity of data acquired and communicated among the elements of the system. The level of data integrity and reliability is especially important to facilities management systems which seek to achieve robust control of an environment or process by updating manipulated variables to desired states based on measured parameters of the process. Current systems fail to develop and effectively use reliability or data integrity indicators to produce controlled variations of system performance based on the quality of measured data. In conventional system, operation of proportional plus integral plus derivative controllers used in Facilities Management Systems has traditionally involved control of one loop at a time. Multiple instances of such PID loops have not been controlled using a single software approach due to the variations in such loops. Another factor in the design of facilities management and other systems is the design of control systems which are tolerant of system component failures has been an objective for decades. The motivations for increasing levels of fault tolerance include improved human safety, equipment safety, and control of system performance. The most basic form of fault tolerance involves the application of fail-safe system components. In the traditional pneumatic HVAC controls industry, this often involves the use of normally open valves for heating applications and normally closed actuators for mixed air damper applications. Under these circumstances, a system failure (e.g., loss of compressed air, temperature transmitter failure) returns the mechanical system to a safe, although potentially uncomfortable and uneconomic state. In electronic control systems, electric actuators can be specified with automatic spring returns to provide a similar fail-safe functionality. With the introduction of digital control systems, a higher degree of fault tolerance is possible. The digital controller has the ability to trap specific input signal fault conditions, such as a sensor malfunction, and can then partially compensate for that failure in software. The flexible software response is referred to as a fail- soft feature. Examples of fail-soft functionality in the event of a sensor failure include: 1) maintaining the current control signal, 2) commanding the control device to an intermediate safe position, or 3) computing an appropriate control signal based on an alternative strategy. Aside from the application of redundant components, the use of an alternative or backup control strategy provides the best opportunity for simultaneously maintaining equipment safety, occupant comfort, and energy efficiency in the event of an instrumentation failure. An extension of the fail-soft concept involves the application of an intelligent strategy which individually adapts to a specific controlled process and can satisfy nominal system performance requirements over extended periods of time in the event of a failure. Some intelligent strategies are currently applied in advanced military aircraft and nuclear power plants. The method and apparatus described below is an intelligent backup control strategy to be applied in the HVAC industry. Facilities management systems employ both demand limiting and load rolling for energy optimization. The demand limiting feature monitors the current energy consumption over a sliding interval of time corresponding to the demand interval used by the power company. This feature controls the system to maintain an average energy consumption below an established limit. Conventional systems which do not use historical data to predict future demand, tend to overreact to sudden peaks in energy consumption, and as a result shed excessive loads. The load rolling feature reduces total energy consumption by periodically shutting loads off for short periods of time. The user specifies a target amount of load to remain off. Systems that do not accommodate environmental conditions may cause extremes in areas controlled by loads that are shed for too long a period of time. In a distributed facilities management system, loads might be distributed over multiple control nodes. However, one node runs the demand limiting and load rolling features, shedding loads on its and other nodes in the system. After shedding a load, a problem can occur where communications can be lost between the node issuing the shed command and the node that contains the load. In such a situation the load could remain shed indefinitely causing environmental extremes in areas controlled by the load. The node commanding the load shedding may also experience time delays and information bottlenecks in its attempt to monitor every load and its environmental overrides. Another important factor in achieving high level performance of facilities management systems is reducing effects of both external and self- induced noise. In addition, it is necessary for a system to provide immunity to external electromagnetic interference (EMI) and prevent the generation of unwanted levels of EMI which may effect other systems. This is particularly critical where wide dynamic range is required, for example, to accommodate both extremely low level sensor signals and much larger digital and binary signals. Systems which employ a single power supply and other known power supply filtering techniques may fail to provide sufficient isolation from spurious signals or sufficient reliability, due to their reliance on a sole power supply. Similarly, many contemporary systems also fail to sufficiently isolate digital signal lines from sensors which are subject to extremes of environmentally induced spurious signals. This is particularly important in systems employing bus structures and networks. An unpredictable variation in a single sensor on a network can result in systemic problems, if the signal is communicated to other devices connected to the same communications media. A further need for isolation from effects of failures of devices interconnected on a common communications media also exist. Omitting such isolation exposes networks and sub-networks to complete breakdown should a failure occur in a single node. Thus, it is desirable at all levels of system interconnection to provide for isolating interconnected system components from each other. Similarly, it is also desirable to provide graceful system degradation in the presence of a failure. Other limitations of facilities management systems arise in the connections of various devices to control nodes. Multiple devices, especially if connected on a bus, introduce noise on the transmission medium. In addition, the transmission medium may be susceptible to noise from other internal and external sources. Both differential noise, in which opposite polarity voltages appear on two leads of a transmission medium, e.g., a twisted pair, and common mode noise, in which the same noise is induced on both lines of the bus, are possible. Even where optical coupling of devices to the bus is used, it may be necessary to take steps to further reduce noise effects. Summary of the Invention To address the limitations of the related art described above, the invention provides a method and apparatus for substantially isolating the software providing the interface between higher level software features and operational units and for allowing changes to operational units without requiring extensive higher level software changes. An intermediate level of software treats all inputs and outputs in the same way independent of the characteristics of the operational units. A further intermediate level of software controls interfaces between a higher software level and operational unit hardware. The first intermediate level of software treats all higher level software requests for data from operational units in the same way. The further intermediate level of software categorizes hardware units into types which can be manipulated according to a standardized approach for the type. , All intermediate levels of software have a database of attributes and a common method and set of messages for manipulating the attributes which provides broad data constructs for accommodating remotely controlled operational units. Such data constructs minimize the need to reproduce the same data or data attributes for multiple operational units. The data constructs are provided with attributes defining paths to at least one other data construct. Thus, the invention provides data constructs containing attributes of associated data constructs. The invention provides a flexible, reliable method of accessing data among nodes in a distributed system with a method of accessing data in a distributed system without requiring a central look up node and without requiring a search of the entire network on every reference to the data. This method of accessing data within a distributed system assigns a unique name to a data element when it is first defined. The unique name of the data element is bound to a host node at the time the data element is first accessed. This allows accessing data in a distributed network using a multi-level naming convention based on a user defined name and the physical location of the data element on the network. In this naming convention, a user assigns names to data elements independent of where the data element is located on a network. According to the naming convention, a name is bound to a unique address, such as a physical location and data base location within the node, when it is referenced for the first time in the running network. Subsequent references to data elements are provided by using the user assigned name bound to the unique address. It is also useful to provide a distributed system having time synchronization of system nodes and synchronized data bases of global variables among the nodes. Nodes periodically broadcast their presence on a system using time stamps indicating when the node's data base of global variables was last updated. As a result, it is possible to coordinate all nodes on a network to incorporate the global data base of the node having the most recently updated global data base. The invention further detects and reports inconsistencies and duplication of data constructs in their respective data bases. This is accomplished in the system by recognizing directory entries in the nodes' data bases which have multiple definitions in other locations on the system. Nodes without routing tables identify other nodes with routing tables in order to identify paths to route download requests from the nodes without routing tables to devices containing download information. Within the system, data constructs allow high level features in the nodes to be notified or triggered by changes of state in attributes and objects on other nodes. In addition, changes in locations of objects and attributes in the system can be detected to notify features activated or triggered by the objects or attributes. Results produced by system processes are reported to appropriate display and storage devices. Thus, the system according to the invention detect changes in physical locations of display and storage devices and route reports to the correct devices. To reduce the volume of data traffic required to produce standard or predefined summaries of data for storage or display, a system or method according to the invention filters data used in producing standard summaries. This is accomplished by defining criteria for data retrieval in a high level feature directory routed to a task in the same node as a directory of the data to be retrieved. The system can retrieve standard summary data according to nodes identified in a directory and assemble the data in the node containing the directory into a message for transmission to a feature generating the summary. In another aspect of the invention it is also desireable for a system to allow devices not included in the original network configuration to communicate with configured nodes on the network. Thus, non-configured devices can receive messages from configured nodes on the network. Such non- configured devices can access networks which employ either adaptive or non-adaptive routing strategies without requiring the down loading or updating of static or dynamic routing tables in existing nodes. A system according to this aspect of the invention allows such non-configured devices to be attached to a first configured node on a network using one of either an adaptive or non-adaptive routing strategy and to receive messages from other nodes on other networks using the same or a different routing strategy, without requiring shutdown of the system. Access to a communication system on demand by processing devices is provided without requiring their membership in a network on the system. Such processing devices access a system to perform diagnostics, maintenance, and administrative functions from anywhere in the system. These processing devices access a data communication system on demand without requiring changes to global variables or static or dynamic routing tables or directories. The invention also provides a data communications approach which allows access to data remote from the requesting processor without creating unnecessary message traffic. It further reduces unnecessary access to sensor data in a facilities management system and prevents slave controllers from providing unnecessary information to a master controller which does not require it. Access to sensor information is controlled based on the expected rate of change of the parameter measured by the sensor. A master controller regulates access to sensor information by remote slave controllers according to the validity of the sensor and the data transfer needs of the system. In addition, it is possible to regulate access to data by remote master controllers connected on a network bus to a master controller regulating the data producing processor on a local bus. It is another aspect of the invention to test reliability of data elements and tag a status of the tested data with an indicator of its reliability. It is also useful to report the reliability indicators associated with data elements throughout the system. By associating a reliability indicator with data used in intermediate calculations throughout a system, a reliability indication of a result obtained through one or more calculations can be determined. A portion of the software is provided in the form of a generalized proportional plus integral plus derivation control object to translate commands from high-level software features in control systems and convert these commands to appropriate signals which activate and control a proportional plus integral plus derivative (PID) control loop (e.g., activate and control devices as part of a closed top control process) . This software object also provides a predictable and controlled transfer from control by a scheme outside a PID loop to control by PID automatic control means. Other features of a software object include eliminating the hysteresis effect that a controller may experience between the output controlling a process and a sensed feedback from the process and providing an adjustable dead band to PID control. The software mechanism in the form of a PID device object also provides the ability to interface actual PID hardware to other software objects and a scheduling means for PID loops. In view of desirability of implementing improved back-up control strategies in HVAC applications, the invention provides an HVAC control system with the ability to maintain control over a process when an input variable becomes unreliable. Operation of a process, even when feedback from the process is lost or unreliable, is provided based on a model of the system or process and other system inputs. A set of parameters is locked at the time that the system or feedback becomes unreliable. Thus, a manipulated variable is adjusted based on the state of process variables just prior to the system or process becoming unreliable and based on current status of process variables. This also provides the ability to control response of an HVAC system to a changing setpoint in the presence of an unreliable variable. Another aspect of the invention provides the ability to predict energy demand in a future demand time period based on the current demand and historical collected data. With this information, the system can automatically vary on and off times of a load to accommodate the predicted energy demand, thereby maintaining average demand below a target. In addition, it is possible to adjust operating time of a load to minimize costs by shifting energy consumption from expensive periods of high demand to less expensive periods of lower demand and to adjust the operating time of a load to accommodate environmental conditions in areas affected by the load. In another aspect, communications between demand limiting and load rolling features in one node and objects in other nodes do not become impaired by excessive traffic. Loads shed as a result of demand limiting remain shed until communications with the demand limiting feature are restored. A load shed as a result of load rolling is restored even if communication with the node containing the load rolling feature are not restored. Shed and restore characteristics are provided as attributes as part of an object rather than as part of a higher level software feature. A message to an object manager redirects load related characteristics for the load local to the node using a restore task localized within the node. To reduce noise coupling among local devices connected to a node, optical coupling of signals between the nodes and local devices connected to a local bus is employed. Effects of differential mode noise induced on the bus are ameliorated by biasing the leads of the bus to a predetermined voltage. Optical isolators are protected from large common mode voltages by using tranzorbs and metal oxide varistors to shunt such high voltages safely to ground. Indicators of when a node is transmitting and receiving data are provided. Separate digital and communications power supplies to portions of the local bus interface circuits are provided. An optocoupler isolates the digital and communications power supplies. As a result, a system can be operated with no ill effects with up to 2500 volts, peak, noise on the communication power supply. In one aspect of the invention, software is organized into multiple levels. The highest or "features" level communicates with a software object level containing software object database managers and databases. The software object level treats all inputs and outputs to and from the features level the same way. In addition, the software object level communicates with a lower intermediate level, the hardware object level. The hardware object level contains a hardware object database manager and databases. The hardware object level operates to mask the differences between individual operational units to the software object level. The hardware object level categorizes data acquisition units so that additional units of a known type can be added with no more than a minor database change. Additional types of operational units can also be added while software changes are confined to the hardware object level. Thus, new units can be incorporated without any major impact on overall system software. The software also employs points and pseudo points. One or more attributes define a point as a vector quantity. The values of the attributes which characterize the vector quantity are obtained from operational units, such as sensors. Each individual point is an independent vector quantity which is defined without reference to any other point in the system. A pseudo point is also a vector quantity defined by attributes. However, at least one of the attributes of a pseudo point identifies an associated point or attribute of a point. Additional attributes of the pseudo point are then obtained from the identified point to facilitate intermediate calculations without requiring repeated access to the operational unit associated with the point. Other aspects of the invention are accomplished by a multi-level naming convention. First, each data element is assigned a name unique to the system, so that it is a unique identifier which is used only for that piece of data. The name assignment is done when the data element is created in a network generation process. When the name is referenced the first time in the running network, the name is assigned or bound to a unique address identifying both the node location and the data base location within the node. This is done by searching the network for the data element by name the first time it is referenced. Thereafter, this bound reference is used to locate the data element at each subsequent reference to that data element during run time. In another aspect, consistency among global variables in the nodes is maintained. At regular intervals each node broadcasts its presence and a time stamp indicating the most recent update of its data base of global variables. The nodes receiving the broadcast compare their time stamps with the one most recently broadcast. If the time stamps are not the same, the receiving node requests the broadcasting node with the latest data to download the more recent global variable data base. This occurs so that all the nodes have the most recent global variables. In another aspect of the invention a facilities management system is divided into a plurality of individual systems with each of a plurality of nodes having a list of all the names in systems defined on the nodes. In order to allow the systems to be distributed over one or more interconnected networks, the system definitions include a directory of objects for the system stored on the system defining node. The directory defines which node the object is located on so that it is not necessary for all the objects of the system to be resident on a single node. When objects are moved around from the control of one node to another, the directories are updated. Another aspect of the invention involves using a single node to coordinate timing within the system. The time keeping node monitors calendar date and time of day to assure that regularly scheduled activities take place as required. In addition, should the node monitoring calendar date and time become disabled, a second node performs this function. Calendar date and time of day information also can be maintained in all the nodes distributed on a system. The nodes are time synchronized by redistributing to all the nodes date and time information at a fixed time every day under normal operating conditions. This permits routine updating and synchronization on a regular basis of the plurality of nodes. In another aspect, nodes are provided the ability to cascade download requests through other nodes. A node without a routing table identifies another node with a routing table which can identify a path to route a download request. Thus, once a first node contains a routing table a second node without a routing table can receive download information from an external device through the node with the routing table. In another aspect of the invention, triggering attributes of objects is accomplished in response to changes of state. Object managers and high level software features "sign-up" to be notified when specific events occur. For example, an alarm might be triggered when a sensor exceeds a known threshold. It is not necessary that the object manager which handles the sensor information and the feature be located at the same node. The feature need only "sign-up" to be notified by the appropriate object manager. However, in the event that the object manager is changed the sign-up becomes invalid. This is detected and the feature is notified. In another aspect, the routing of reports is distributed. Routing information is retained within each node on the network as global data. Reports emanating from the node are routed through a report router task for ultimate distributions to the destination device. The report routing task acts as intermediary between input/output routines of the nodes. The report router determines if the input/output routine can route the report to a destination device. If not, the report router determines if a second or default device is available. If not the message is discarded and the report routers are so notified. If a default device is available, the report is routed to the default device. In another aspect, the volume of data traffic required to produce the standard or predefined summaries of data for storage or display is reduced. This is accomplished by localizing filtering of data at the node of which the particular object directory of interest is located. Standard summary data is obtained from the nodes identified in a directory of a first node. The data need not be obtained from devices connected to the first node, but obtained from the nodes identified in the directory. When the data is obtained it is assembled in the node containing the directory into a message for transmission to the high level software feature generating the summary. The high level software feature may be located in any node. In another aspect of the invention a non- configured device can be attached to a port on a configured node of a network. The non-configured device, which contains its own process identifiers, communicates via that port with the configured network node. The configured network node communicates with other configured network nodes to route messages from the non-configured device to their destinations. Destination nodes recognize the message source as the configured network node or as a non-configured device dropped from a port on a configured node. Thus, at the destination node, responses generated are transparent to the status of the source as a non-configured device. The final destination node responds as though the message is from a configured node and the response message follows the same or an alternate data communication path back to the configured node having the non- configured device connected to its port. Based on communications over a drop between the non- configured node and the configured node, the configured node provides the message to the non- configured device which delivers it to a process identified in the message. This allows any configured node to respond to data requests made by a non-configured device. Another aspect of the invention provides a method and apparatus in which a master controller stores sensor values in a data aging table and associates each sensor value with a valid time frame. All requests for data during the valid time frame are serviced by transmitting the value from the data aging table in the master controller. This prevents further data requests to the slave controller and reduces message traffic on either the local or the network bus. This also allows matching the aging timer value to the characteristics of the sensor data. In another aspect, the invention provides an indicator to detect the status of data reliability. Each data element is assigned a reliability indicator which is propagated throughout all the calculations involving the data element. As a result, it is possible to determine an overall certainty of the accuracy of a calculation, since each intermediate calculation also considers the reliability of the data elements. Another aspect of the invention provides a proportional and integral and derivative controller software object which is based on sampling a feedback value at consistent time intervals. The object incorporates the proportional, integral, and derivative terms independently so that the individual terms may be removed. This facilitates having any combination of proportional, integral and derivative controls. The PID software object employs points and pseudo points on which input conditioning is performed and which are processed according to a sample period, proportional band, and other parameters. By outputting a percentage of full scale deflection of a variable, the corresponding output port may be driven. In addition, a fault tolerant control strategy to predict steady state change in a controlled variable for a given change in inlet process conditions can also be used. Applying a simplified model based on measures of effectiveness, the change in effectiveness due to a change in a process variable is derived. Further assuming that the process model will only be valid for a limited region around the current operating point allows calculation of a manipulated variable value based on previous values of the manipulated variable, other manipulated variables, primary and secondary process variables, the initial value of the controlled variable, and a setpoint. By incorporating the setpoint and primary and secondary process variables into a system dependent only on the initial value of the controlled variable, a variable can be manipulated based on current inputs and system history, even though the controlled variable or feedback signal is presently unreliable. In another aspect the invention allows predicting energy demand in a future demand period based on a window of previous energy consumption. In response to the predicted energy demand, commands can be issued to shed loads contributing to the demand so that a demand limit is not exceeded. Loads that are shed either by the demand limiting or load rolling feature will be restored either due to a defineable time period expiring or as a result of an extreme in an environmental condition being detected in an area affected by the load. A high level feature which sheds a load may lose communication with the load since loads are distributed over multiple nodes in a system. To be certain that a load shed as a result of a load rolling command is restored after a prescribed time interval for that load, a restore task is localized within each node. Specific shed and restore characteristics are stored as attributes of the object in the node with the load and not as part of the demand limit/load rolling high level software feature. This allows high level software features in one node to shed loads distributed over the system without requiring that communications be maintained with the load in order to restore the load at the proper time. A localized restore task also will monitor environmental conditions affected by the load and, thus, eliminate the extra traffic on the network by removing that task from the node running the demand limit/load rolling feature. The invention also provides an optical interface to a local optical bus compatible with the RS/485 Electronic Industries Association specification. The interface employs bias circuitry which is used to "swamp out" differential mode noise on the leads of the bus and transorb and MOV circuitry to shunt common mode voltage and excessive differential mode noise to ground. Optical isolators provide isolation between digital and communications power supplies and retriggerable one shots are used to activate data transmission and reception indicators such as LEDs. Brief Description of the Drawings The above objects of the invention are accomplished as described below in accordance with the following figures: Figure 1 is a network control module according to the invention. Figure 2 shows a digital control module according to the invention. Figure 3 shows an expansion module according to the invention. Figure 4 shows a network control unit in a five slot configuration. Figure 5 shows a network control unit in a two slot configuration. Figure 6 shows a single slot configuration network control unit. Figure 7 tabulates modules used in one, two, and five slot configurations of a network control unit. Figure 8 tabulates modules used in one, two, and five slot configurations of a network expansion unit. Figures 9A and 9B illustrate a sample facilities management system configuration. Figure 10 illustrates a lighting controller used in a network according to the invention. Figure 11 illustrates a card access controller used in a network according to the invention. Figure 12 illustrates an intelligent fire controller used in a network according to the invention. Figure 13 illustrates a facilities management configuration for small buildings. Figure 14 illustrates a facilities management configuration for mid-size buildings. Figure 15 illustrates a facilities management configuration for large buildings. Figure 16 illustrates a facilities management configuration for remote buildings. Figure 17 shows one system configuration according to the present invention. Figure 18 shows a more detailed view of various software levels. Figure 19 illustrates the use of points and pseudo points according to the invention. Figure 20 is another overview of a system according to the present invention. Figure 21 is a flow diagram illustrating a first embodiment of the method of the invention. Figure 22 is a flow diagram illustrating a second embodiment of the method of the invention. Figure 23 illustrates a further optimization of the method in Figure 22. Figure 24 illustrates an embodiment of the method of the invention using multiple levels of names. Figure 25 illustrates an example of the invention when a name changes its address within a node. Figure 26 illustrates an example of the invention when a name moves between nodes. Figure 27 illustrates a method of time synchronizing nodes according to the invention. Figure 28 illustrates downloading global variables to nodes on the network according to the invention. Figure 29 is a more detailed illustration of downloading variables according to the invention. Figure 30 illustrates cascading of download devices according to the invention. Figure 31 is a table showing transmission of messages when a download request originates from an archive unit. Figure 32 is a table illustrating a sequence of message passing when a node without a routing table initiates a download request. Figure 33 illustrates triggering of features from attributes of objects. Figure 34 illustrates distributive report routing according to the invention. Figure 35 illustrates filtering of summary report data at local nodes. Figure 36 shows a more detailed description of the events which occur in applying selection criteria to filtered attributes. Figure 37 shows an example of a non- configured device attached to a configured node for communicating over communications links with one or more configured nodes. Figure 38 illustrates the message path between the non-configured and configured nodes in Figure 1 along with various data communication layers. Figure 39 illustrates the transmission of a request from a non-configured device or a response from a configured device. Figure 40 illustrates the receipt of a request from a non-configured device or the receipt of a response from a configured device. Figure 41 tabulates a possible routing strategy for messages between the non-configured device and a configured node. Figure 42 shows the general configuration of a facilities management system. Figure 43 shows a basic configuration in which a master node communicates with slave nodes over a local bus. Figure 44 shows another embodiment in which multiple master nodes communicate over a network bus. Figure 45 illustrates a method of tagging data with reliability indicators. Figures 46A and 46B illustrate processing of a PID Loop Object. Figure 47 shows a typical HVAC control system with a fault tolerant control strategy implementation. Figure 48 shows the phases of implementing a fault tolerant control strategy. Figure 49 illustrates the inputs and outputs of the phases of the strategy. Figure 50 illustrates one configuration of a system with a digital control module and a network controller. Figure 51 shows a configuration of a system with distributed load shedding and localized restore tasks. Figure 52 shows a fault tolerant control configuration. Figures 53A and 53B show process monitoring steps. Figure 54 shows steps in operating a fault tolerant controller. Figure 55 shows steps in switching a manipulating and backup variable. Figure 56 illustrates nodes operating slave devices over a local or slave bus. Figures 57A and 57B illustrate an optical interface between a node and a bus having slave devices. Detailed Description of the Preferred Embodiments Figure 1 shows generally network control module l-l which has a processor 1-3, dynamic random access memory 1-5, and electronically programmable read only memory 1-7. Network control module 1-1 communicates with high speed bus 1-9, the Nl bus, so that network control module 1-1 can be interconnected in a local area network configuration to other network control modules. A plurality of network control modules 1-1 connected over high speed bus 1-9 form a network which can be interconnected through gateways to other networks of network control modules interconnected on high speed buses. Network control module 1-1 further has standard RS-232 interface 1-11 with a plurality of ports to provide communication through a modem over port 1-13, a specialized network terminal over port 1-15 and a computer, or printer over port 1-17. Field trunk controllers 1-19 and 1-21 allow network control module 1-1 to communicate with field devices interconnected on communications media 1-23 and 1- 25. Subnet controller 1-27 allows devices 1-29, 1-31, 1-33 to communicate with network control module 1-1 over N2 bus 1-35. To isolate network control module 1-1 from spurious signals and power surges which may become impressed on N2 bus 1-35, N2 subnet controller 1-27 incorporates an opto-22 interface 1-37, as shown. A network control module according to the invention functions as a central part of a network control unit described below. Network control modules, either alone or as part of network control units, function as controllers for nodes interconnected by the high speed Nl bus 1-9. Thus, a primary function of the network control module is to supervise peer to peer to communications with other network control modules or network control units and operator work stations on high speed bus 1-9. In a facilities management system (FMS) the network control module performs supervisory control of an area of a building. Thus, in accordance with specialized programs, the network control module supervises maintaining environmental conditions according to program parameters and communicating with operational units, such as sensors and other devices connected to the network control module l-l via N2 bus 1-35. Network control module 1-1 further manages communications over a RS-232 interface l-ll to various person machine interfaces (PMI) . Specialized devices in the facilities management system can be connected via field trunk controllers 1-21 and 1-19 and corresponding communication media 1-25 and 1-23. In a facilities management system (FMS) according to the invention, the network control module 1-1, which is sometimes referred to as a network controller, is configured as a plug in module which mates with a connector on a backplane. Figure 2 shows digital control module 2-1 which also interfaces with a connector on a backplane. Digital control module 2-1 includes processor 2-3 and memory 2-5. Memory 2-5 is divided into a static random access memory section 2-7, and electronically programmable read only memory (EPROM) section 2-9, and an electronically erasable programmable read only memory (EEPROM) 2-11. In addition, digital control module 2-1 has input/output sections 2-13 and 2-15. A digital control module 2-1 may also be incorporated into a network control unit according to the invention, as discussed below. A digital control module conditions sensor inputs received through input/output sections 2-13 and 2-15 and reports changes to the network controller or network control module 1-1. In addition, in a facilities management system (FMS) the digital control module performs closed loop control for a plurality of control loops. Thus, closed loop control can be accomplished without a network control module. In addition, the digital control module 2-1 executes commands received from network control module 1-1. Digital control module 2-1 further may accept inputs either directly or through a function module. A function module (FM) also performs conditioning of an input or output signal. While a digital control module according to the invention can accept inputs directly (100-1,000 ohms RTD (resistive temperature device) , 4-20 mA, 0-10 volts DC) or through an input function module, all outputs from a digital control module 2-1 are characterized by function module selection. A function module (not shown) conditions signals but does not perform sophisticated processing. Such function modules, according to the invention, are tailored to accommodate the specific conditioning function required. Thus, a function module may contain sophisticated electronics tailored to perform a specific task or may be as simple as a single resistor. Network control module 1-1 also performs numerous background tasks, as discussed below, to assure that each of the nodes on the system is operating with the same global variables, is time synchronized, and has consistent directories of system names. In addition, software in the network control modules 1-1 to reduce data communications, to track the aging of data, and to provide a uniform means of isolating high level software features from specialized operational units is discussed below. Typical input function modules in a facilities management system include pressure/electric transducers, binary input contacts or AC line voltage conditioners, differential pressure inputs, and binary frequency inputs. Typical output function modules include analog outputs, analog outputs with isolated grounds, electric/pressure transducers, binary polarity reversing, triac incremental function modules, motor start/motor stop function modules, electrically maintained relay outputs, magnetically latched relay outputs, and solenoid air valve function modules. As shown in Figure 3, expansion module (XM) 3-1 according to the invention, includes processor 3-3 and memory 3-5. The memory is typically divided into static random access memory (SRAM) 3-7 and electronically erasable programmable read only memory (EEPROM) 3-9. Point multiplex modules 3-11 provide a configurable input/output for the expansion modules. The expansion module is also a plug in module which plugs into a connector on a back plane in a node of a facilities management system. The expansion modules condition binary, analog and pulse inputs and report changes to the network controller or network control module l-l. In addition, the expansion module executes binary output commands from network controller 1-1. Point multiplex modules 3-11 provide five configurations of expansion modules. These include a first configuration having 32 binary inputs, a second configuration having 8 binary inputs and 8 pairs of outputs using momentary relays, a third configuration having 8 binary inputs and 8 magnetically latched relay outputs, a fourth configuration having 8 analog inputs and a fifth configuration having 8 binary inputs and 8 electrically maintained relay outputs. Network control modules, digital control modules, and expansion modules, can be combined in various configurations to form a network control unit according to the invention. A network control unit (NCϋ) in a facilities management system monitors and supervises heating ventilating and air conditioning (HVAC) , lighting, and building functions. Network control units are interconnected by the Nl bus 1-9. As part of an Nl network, the NCU shares all data with all other NCUs in a dynamic data access relationship. A distributed system is formed because peer-to-peer communications allow each network control unit to access and use data acquired under the control of any other network control unit. Thus, information at any level is accessible to every NCU to integrate and optimize all components within a building. Network control units can also be interconnected to perform other control functions involving the use and monitoring of diverse physical sensors and equipment, such as a broad array of industrial control processes and other processes involving control systems. Figure 4 shows one configuration of an NCU 4- 1 in which five slots 4-3, 4-5, 4-7, 4-9 and 4-11 are available. Slot 4-3 contains a network control module as previously discussed relative to Figure 1. The network control module provides the sole means of communication along the high speed Nl bus 4-15 through communication terminal board 4-13. It should be noted that only a network control module can communicate on the high speed Nl bus 4-15. Slots 4-5 through 4-11 can be occupied by digital control modules, expansion modules, or additional network control modules as shown. Communications between these devices and with the network control module is via the N2 bus 4-16. Slots 4-5 and 4-9 can also accommodate network control modules. These network control modules may also communicate over the Nl bus 4-15 as indicated by dotted lines 4-17 and 4-19 in Figure 4. As shown in Figure 1, network control unit 4- 1 is provided an interface to an operator through RS-232 interface portion 1-11 of network control module 1-1. Using a dial-up modem 1-13, specialized network terminal 1-15 or an operator work station such as a personal computer, an operator may generate or respond to commands and provide program changes and organizing data to user specified data bases. The five slot NCU configuration in Figure 4 also shows connectors 4-21 and 4-23 for a plurality SUBSTITUTE SHEET -45- of input function modules and corresponding input function module terminal boards 4-27 and 4-25. Similarly, connectors 4-29 and 4-31 accommodate a plurality of output function modules and corresponding output function module terminal boards 4-33 and 4-35 are provided. It should also be noted that each individual slot 4-3 through 4-11 is provided with its own power supply 4-37 through 4- 45. Expansion module input terminal boards are provided at 4-47 and 4-49 and expansion module inputs/output terminal boards are provided at 4-51 and 4-53. Line voltage, V, is applied to the power terminal board 4-55. An alternative configuration of a network control unit is the two slot configuration 5-1 shown in Figure 5. Slots 5-3 and 5-5 can each accommodate an expansion module. Slot 5-3 can also accommodate a digital control module while slot 5-5 can also accommodate a network control module. It should be noted that in order to constitute a network control unit, at least one network control module is required. This is because, as previously noted, it is only a network control module which can communicate in a peer-to-peer relationship with other network control units over the Nl bus. Thus, slot 5-5 has a connection to the Nl bus 5-7. Devices installed in slots 5-3 and 5-5 communicate with each other over N2 bus 5-9. Both the Nl and N2 buses are connected to communications terminal board 5-11 to provide further communications with the remaining parts of the system. SUBSTITUTE SHEET In a manner analogous to that discussed in Figure 4, a plurality of input function modules can be located at connectors 5-13 and the plurality of output function modules can be located at connectors 5-15. Input function module terminal board 5-17 and a corresponding output function module terminal board 5-19 are also provided. Similarly, expansion module input terminal board 5-21 and expansion module input/output terminal board 5-23 provide access to the expansion module. It should be further noted that devices in slots 5-3 and 5-5 also have independent power supplies 5-25 and 5-27. Line voltage, V, is provided to power terminal board 5- 29. Figure 6 shows a single slot configuration according to the invention. Slot 6-3 can contain a network control module in which case the device operates as a network control unit with the ability to communicate on a peer-to-peer basis with other devices via the Nl bus 6-5. Communication with devices on the N2 bus external to the NCU 6-1 is over N2 bus 6-7. As Figure 6 shows, line voltage, V, is connected to power terminal board 6-9 and power supply 6-11 supplies the device in slot 6-3. Figure 6 also shows that device in slot 6-3 can be an expansion module. Thus, the single slot configuration in Figure 6 also has expansion module input terminal board 6-13 and expansion module input-output terminal board 6-15. SHEET SUBSTITUTE As previously stated, a network control unit must have a network control module in order to SUBSTITUTE SHEET 50 accomplish peer-to-peer communications over the Nl bus. However, as the single slot configuration in Figure 6 shows, it is possible for a device to be constructed having an expansion module without a network control module. Since an expansion module could not communicate over the Nl bus, the device can not be a network control unit. It is possible, according to the invention, to construct in either the 5 slot back plane shown in Figure 4, the two slot back plane shown in Figure 5 and the one slot back plane shown in Figure 6 a device which does not have the capability of communicating over the Nl bus. Such devices are called network expansion units (NEU) . Network expansion units serve two functions. First, they serve as a collection platform for I/O points in order to increase the point and control loop capacity of an NCU. Second, network expansion units can be remotely located from an NCU to monitor and distribute control to points and then transfer the data from these points back to the NCU over the N2 bus. Since the back planes can be used to construct either a network control unit or a network expansion unit, alternative configurations are possible. Figure 7 shows fully loaded alternative configurations possible for network control units having 1, 2 and 5 slot back planes. Figure 8 shows fully loaded possible configurations of network expansion units having 1, 2 and 5 slot back planes. SUBSTITUTESHEET -3 i - Figure 9 illustrates a possible configuration of a facilities management system according to the invention. Five slot NCU 9-1 communicates with one slot NCU 9-3 over Nl bus such as ARCNET 9-5. Nl bus 9-5 is also connected to personal computer 9-7. Personal computer 9-7 can be used as a download device to download new information and data bases to NCUs 9-1 and 9-3 and other devices connected to NCUs 9-1 and 9-3. Nl bus 9-5 is connected to communication terminal board 9-9 in NCU 9-1 and terminal communication board 9-11 in NCU 9-3. Within NCU 9-1 Nl bus 9-13 is connected to network control module 9-15. Since this is the only network control module shown in five slot NCU 9-1, there are no further connections within the five slot NCU to the Nl bus 9-13. Five slot NCU 9-1 also has expansion modules 9-17 and 9-19 and digital control modules 9-21 and 9-23. These modules perform the functions discussed previously and are interconnected with the five slot NCU via N2 bus 9- 25. An interface communicates directly with the five slot NCU Nl and devices on its N2 bus via lap¬ top PC 9-27. As Figure 9 shows, lap-top 9-27 is connected to an RS-232 interface 9-29 which is part of network control module 9-15. A network terminal unit for specialized network terminal 9-31 is also accommodated on RJ-11 interface 9-33. Network control module 9-15 also has sub-modules 9-35 and 9- 37. Such sub-modules may include devices such as subnet controller 1-27, field truck controller 1-21 and RS-232 interface 1-11. Function modules, for SUBSTITUTE SHEET, -51a- example, 9-41a through 9-41f are. also SUBSTITUTE SHEET -52- used in the five slot NCU 9-1. As Figure 9 shows, each device in the five slots has its own power supply, for example, 9-43a through 9-43f. The power supplies all receive line voltage or AC power through power terminal boards, for example, 9-45a through 9-45d. The individual power supplies exist to isolate spurious signals and noise in one device from being communicated via the power supply lines into a second device. One slot NCU 9-3 is formed from a single network control module 9-47. Within network control module 9-47 sub-module 9-49 provides an interface to a personal computer 9-51 and RS-232 interface 9-30 is provided to printer 9-53. The NCU may also have RJll interface 9-32. Network control module 9-47 communicates from network control unit 9-3 over N2 bus 9-55 to fire system 9-57 and access control system 9-59. Fire system 9-57 is used to detect dangerous smoke and fire conditions in the building and access control system 9-59 is used to provide security services. Such systems are known in the art and are shown to illustrate the capabilities of a facilities management system according to the invention. Five slot NCU 9-1 communicates over N2 bus 9-61 with one slot expansion unit 9-63, two slot network expansion unit 9-65, application specific controller 9-67 and lighting controller 9-69. One slot network expansion unit 9-63 has an expansion module 9-71 which communicates with the N2 bus 9-61 via communication terminal board 9-73 SUBSTITUTESHEET -52a- within the one slot NCU 9-63. Expansion module 9-71 has its own power supply 9-75. As with expansion SUBSTITUTESHEET -03- modules 9-19 and 9-37 in five slot NCU 9-1, expansion module 9-71 may have any of the five configurations previously described. As previously noted, the expansion modules condition binary, analog and pulse inputs, report changes to the network controller and execute binary output commands, which command a connected operational unit to one of two stable states, from the network controller. Two slot network expansion unit (NEU) 9-65 has expansion module 9-77 and digital control module 9-79, each with its own power supply 9-81 and 9-83, respectively. Function modules, for example, 9-85a through 9-85c interface with digital control module 9-79. Both the expansion module 9-77 and the digital control module 9-79 are connected to N2 bus 9-61 within the two slot network expansion unit 9-65 to communication terminal board 9-87. This provides access to N2 bus 9-61 for communications with the rest of the sample FMS configuration shown in Figure 9. Specialized lighting controller 9-69 is also attached to the N2 bus 9-61 in order to receive commands and provide lighting status information to five slot network control unit 9-1. Known application specific controllers, for example, 9-67 can also be attached to N2 bus 9-61, according to the invention. Such application specific controllers perform dedicated tasks while communicating over N2 bus 9-61. The overall software structure to accommodate various network SUBSTITUTESHEET -54- expansion units and application specific controllers is discussed below. Figure 10 is an expanded view of lighting controller 9-69 in operation on the system. Figure 10 shows lighting controller 10-1 connected over N2 OPTOMUX bus 10-3 to network control unit 10-5 which communicates with operator work station 10-7 over Nl bus 10-9. NEU 10-15 is also shown connected to the N2 bus. The lighting controller has 32 override switch inputs 10-11 and forty relay outputs. Forty latching relays are possible or 20 remote relays 10- 13 via a low voltage cable connect are also possible. Figure 11 further illustrates an access control system such as that described at Figure 9, 9-59. Here card access controller 11-1 communicates with network control unit 11-3 via N2 bus 11-5, e.g. an OPTOMUX bus. To provide security, the card access controller 11-1 is connected to a smart terminal interface 11-6 with a reader 11-7, such as a Weigand effect, barium ferrite, or magnetic strip reader and 8 alarm inputs 11-9. The card access controller also accommodates 8 proximity readers 11- 11 and communicates over RS-232 interfaces to CRT display 11-13 and printer 11-15. Typically, one access controller would be used for each network control unit. The N2 bus may also accomodate other units such as NEU 11-17, while the Nl bus 11-21 may be connected to other units such as workstation 11- 19. Figure 12 shows a fire system as in 9-57 SUBSTITUTE SHEET -54a- operating on a facilities management system. Network control unit 12-1 communicates with operator work station 12-3 and other network control units over Nl bus 12-5. N2 bus 12-7 is connected to intelligent fire controller 12-9 which receives inputs from a fire detection/signalling loop 12-11. Smart detectors, for example, 12-13a through 12-13c, detect smoke, SUBSTITUTE SHEET 55 thermal conditions and alarms activated at pull stations. Also connected to the fire detection signal loop 12-11 is control module 12-15 which activates a signalling device. Monitor module 12-17 monitors the status of pull stations 12-19, heat detectors 12-21 and water flow alarm switches 12-23. Intelligent fire controller 12-9 is also connected over an RS-485 bus 12-25 to annunciators 12-27. Similarly, intelligent fire controller 12-9 communicates over RS-232 interface to CRT display 12-29 and printer 12-31. The N2 bus. 12-7 can also be connected to binary input expansion module 12-33 which itself is connected to switch panel 12-35. The binary expansion module 12-33 and switch panel 12-35 can operate together to form a smoke control station which transmits information to network control unit 12-1 and intelligent fire controller 12-9 over N2 bus 12-7. Figures 13-16 illustrate the use of various configurations according to the invention in different size buildings. Figure 13 shows a facilities management system configured for a small building. This is a stand-alone configuration in which the network control unit automatically controls and optimizes heating, ventilating, air conditioning and other electro/mechanical building systems with directly connected input/output points. Using a local I/O device 13-1, such as a network terminal, an operator can set up a network control unit 13-3, having functions and schedules, with adjustment and override capabilities. N2 bus 13-5 -56- provides communication from the network control unit to the controlled system shown generally at 13-7. Such a system may have temperature sensor 13-9, flow controller 13-11 and chiller 13-13. Figure 14 shows a typical configuration for a mid-sized building in which several network control units, for example, 14-1, 14-3 simultaneously manage heating ventilating and air conditioning, and various other electro/mechanical systems. NCUs 14-1 and 14-3 can communicate with each other through high speed Nl bus 14-5 and with operator work station 14-7. NCU 14-3 has expanded capacity and range by implementing remote network expansion units 14-9 and 14-11. This eliminates the necessity of wiring line voltages for the separate devices back to the network control unit 14-3. Local input/output to network control unit 14-1 is provided by local I/O device 14-13. Both network control units 14-1 and 14-3 communicate with their respective control devices 14-15, 14-17, 14-19, 14- 21, 14-23 and network expansion units over an N2 bus 14-15, 14-27. Figure 15 shows a facilities management system configured for a large building. In Figure 15, multiple network control units 15-1, 15-3, 15-5 are interconnected over the Nl bus 15-7. In addition, a plurality of operator workstations such as 15-9 and 15-11 are also connected to the Nl bus. For example purposes. Figure 15 shows network control unit 15-3 connected via its N2 bus 15-13 to card access controller 15-15 with proximity reader SUBSTITUTESHEET -56a- 15-30 and smart terminal interface 15-32 connected to magnetic strip reader 15-34. Card access controllers were discussed relative to Figure 11. Figure 15 further shows network control unit 15-5 connected over its N2 bus 15-17 to fire controller 15-19 with fire detection/signalling device loop 15- 28. Such fire controllers were discussed relative to Figure 12. Network control unit 15-1 is connected over its N2 bus 15-21 to various control systems, for example, 15-23 and 15-25. In addition, local input/output to network control unit 15-1 is provided via local I/O terminal 15-27. According to the invention, a facilities management system can also be configured for remote buildings. Figure 16 shows such a system. As shown in Figure 16, remote links can exist either on the Nl or the N2 bus. Operator work station 16-1 is directly connected on a Nl bus 16-3 to network control unit 16-5 and network control unit 16-7. Network control unit 16-9, however, is connected to the Nl bus 16-3 via remote links 16-11. Network control unit 16-7, directly connected to operator work station 16-1, is further connected over its N2 bus 16-13 to controller 16-15 and 16-17. Similarly, NCU 16-9 is directly connected over its N2 bus 16-19 to controllers 16-21 and 16-23. Local I/O to network controller 16-9 is provided by local I/O terminal 16-25. In contrast, network control unit 16-5 is directly connected over an N2 bus 16-27 to controller 16-29 and 16-31 but is connected to controller 16-33 over remote link 16-35. Thus, according to the invention, peer-to-peer communication over the Nl bus can be accomplished by a remote link and master/slave communications over SUBSTITUTE SHEET 58 the N2 bus can also be accomplished by a remote link. According to Figure 17, a plurality of network controllers 17-1 each having a processor 17- 2 and a memory 17-4 are connected by high speed bus 17-3 to form, for example, a networked Facilities Management System (FMS) 17-6. It should be noted that processor 17-2 may be centralized or distributed to accommodate software layers in the node as discussed herein. Each network controller functions as a master control node for operational units attached to it and incorporates several layers of software. The software levels are structured to provide increasing isolation between the software levels and the operational units. The highest software level is the features level 17-5. Features level 17-5 implements specific functions to be performed by the network controller in operating the facilities management system. One example of a specific function would be a user display tabulating or graphically showing certain values. Features contain a control program and a list of data objects on which the control program operates. Any number of high level software features can be implemented depending upon the requirements of the system and the capabilities of the master control node. Some other examples of features performed in a facilities management system would include trend analysis, totalization, and other statistical features providing measures of facilities management systems performance. An -59- important factor is that the increasing level of isolation from the hardware allows the software features to be unaffected by changes in the facilities management system hardware. Software features at the highest level communicate with the software object level 17-7. The software object level is an intermediate level which determines how to carry out the action requested by one of features 18-21, 18-23, 18-25 at the features level 18-5. Information is passed between the software object level 17-7 and 18-7 and the features level 17-5 and 18-5 independent of differences at the lower levels of hardware. Similarly, the software object level forms an interface with another level of software called the hardware object level 17-9 and 18-9. The hardware object level allows for a common interface to be established between the software object and hardware object levels regardless of the peculiarities of operational units, such as sensors and other data acquisition and control instruments, connected to the network controller. This is accomplished by configuring the hardware object level to mask the differences between the operational units to the various entities in the software object level 17-7 and 18-7. In accordance with requirements of local bus communications interface 17-11 and 18-11, network controller 17-1 communicates over local bus 17-13 with slave controllers, for example Type A 17- 15, 17-17, and Type B 17-19. As shown in Figure 1, any number of types of slave controllers is SUBSTITUTESHEET -59a- possible. The slave SUBSTITUTE SHEET -60- controllers are connected to operational units, for example, to sensors T lf T 2 , T 3/ S w S 2 , S 3 . Such sensors are binary or analog field sensors which read values of real world data (e.g., outdoor air temperature) . Figure 18 provides a more detailed illustration of the configuration described in Figure 17. The software object level contains a plurality of software object managers 18-27, 18-31, 18-35. A software object manager is a database manager which handles all requests for a particular type of software object. An object is a named data element stored in the network controller. Objects are categorized in types and each instance of an object has its own set of data, such as object name, current value, alarm limit, etc. Therefore, each software object manager is associated with a corresponding database, 18-29, 18-33, 18-36. One example of a software object manager is an analog input object manager 18-27. This would be the database manager for all instances of analog input objects, such as instances Tl, T2, T3 of temperature objects T in the following example. Another is a Binary Input Object Manager 18-31. All of the elements of the database for a given manager are objects of the same type. In the following example, the software objects include analog input points, and binary input points. Each object type may have several instances, each of which has its own set of data values called attributes. For example, the analog input objects stored in database 18-29 are SUBSTITUTE SHEET -50a- each an instance of a type of object. Each of these SUBS TI T UTESHEET -61 - three instances has its own set of attributes. These attributes are data which includes the object name, the current value, the alarm limits, etc. The hardware object level contains a similar plurality of hardware object managers 18-37, 18-41, 18-45. Each hardware object manager is a database manager which handles all requests for a particular type of hardware device on the local low speed bus 17-13 connecting the network controller to the slave hardware devices 17-15, 17-17, 17-19. For example, a slave controller type A hardware manager 18-37 is the database manager for all slave controller objects of type A (Al, A2, in the example given below) . As with the software object managers, each hardware object manager has a database 18-39, 18-43, 18-47 associated with it containing all objects of that type. For example, database 39 for Type A hardware objects includes Al data 18-49 and A2 data 18-51. Each object has a set of attributes unique to that particular object. Transparency is achieved at two levels. First, software objects are transparent to features; and second, hardware devices or operational units are transparent to software objects. These transparencies are best illustrated by examples. In the first case, the transparency of software objects to features, assume Feature x, 18-21 needs to read a current value field or attribute of sensor T2. This is accomplished by directing the request from Feature x to the software object manager controlling T2. As shown in Figure 17, in this case T2 is SUBSTITUTESHEET 62 controlled by the Type A slave controller 17-17. The analog input object manager 18-27 is responsible to identify the data structure of T2 and return the attribute required by the feature, e.g. the value attribute,to Feature x. As a result. Feature x need only understand the various possible types of data that can be returned as single values and it does not need to know the entire database structure for an analog input object. Feature x also need not be concerned with the particular object type when it requests the current value of an object. Because all information is transferred between the Features level 17-5 and 18-5 and the software object level 17-7 and 18-7 in the same way, the feature need only ask for the current value of an object. Thus, the method for requesting the current value of an analog input object and the value of a different type object, such as a binary input object, does not vary. Feature x only sends a request for the current value attribute to the appropriate object manager. The feature uses the object type only to determine which software object manager controls the data. The actual request issued by the feature for the value is the same regardless of which type of object is being queried. This avoids requiring high level software features to request current value differently for each different object type. An added advantage of this approach is that the feature can always obtain the information the same way regardless of where the hardware is located 63 in the system. Because the feature only requests the object by name, the feature is insensitive to the physical location in the system of the hardware which produces the named object. Thus, hardware differences and physical location of hardware are masked out by the hardware and software object managers. The software object database managers and the hardware object database managers transfer information as previously described and shown in Figures 17 and 18. It should be noted that this is for illustration purposes only and that any configuration of information transferred is possible depending upon the functions performed by the software object database manager and the data provided by the hardware object database manager. Therefore, features are not concerned with the type of slave controller hardware device to which actual sensors or data acquisition or control instruments are attached. When a feature requests the values of the attributes of an object, it is insensitive to the type of slave controller used to manage the sensor which generates the raw data. The software and hardware object levels isolate the features and present the same set of data values the same way to all features for a given object type regardless of the physical slave controller to which the operational unit is attached. Thus, the features need not be changed for each type of slave controller. 64 This leads to the second level of transparency, the transparency of hardware devices to software objects. By interposing a hardware object manager between the software object managers and the slave controllers, it is possible to mask the hardware differences from the software managers. This frees the software object managers' processing capabilities in the node to perform higher level control and reporting of predefined conditions. For example, software object managers report alarms, and notify high level features of changes to act as a trigger mechanism independent of the hardware used to generate the data. One example based on Figure 18 occurs when Feature x 18-21 reads the values of analog type temperature points Tl, T2, and T3. As previously discussed, the feature is not concerned with the hardware and therefore makes the same request for each temperature point to the analog input object manager 18-27. This is because the object requested is of the analog type. The analog input object manager 18-27 itself is also not concerned with the slaves on which Tl, T2, and T3 are located. As far as the Feature x, and analog input object manager 18-27 are concerned, all communications to the various hardware managers are the same for Tl, T2, and T3. The analog input object manager 18-27 requires a plain floating point (real) number, such as 72.3°F from the hardware object level 17-9. The hardware object managers 18-37 and 18-41 for slave 65 types A and B condition the data to supply the analog input object manager 18-27 with values of the required type. In order to determine the value, any number of individual calculations in the hardware object manager may be required. For example, assume the value of the temperature sensor arrives at the slave controller as a count, such as a digital count produced by an analog to digital converter, which must be spread over a predefined range to compute the floating point value. Further modifications may be required by a span equation, a square root equation, and a filter before the final temperature value of the sensor is obtained. As shown in Figure 17, Type A slave controllers 17-15 and 17-17 deliver Tl and T2 raw data. Type B slave controller delivers T3 raw data. Assuming that controllers A and B have completely different levels of capability, the differences in the controllers would create significant problems in existing computerized facilities management systems. For example, one controller may implement a square root equation while the other may not, or the controllers may have different range equations. In conventional facilities management systems, the high level software would be required to compensate for these differences. However, in the present invention, the hardware object managers for the slave controllers access the node processor (or a separate processor) to condition the data and mask these differences from the analog input object manager 18-27. 66 Assume that Type A slave controllers 17-15 and 17-17 are highly simplistic devices which provide only the analog digital count to the network controller. In this case, the hardware object 18-37 manager for type A slave controllers must perform the other calculations necessary to obtain the final temperature values Tl and T2 to be provided to the analog input object manager 18-27. In contrast, assume slave controller type B is a highly sophisticated device which performs most of the ranging and filtering prior to sending the information on to the network controller. In this case, the hardware object manager 18-41 for type B controllers performs relatively little processing. In either case, the processing performed by the hardware object manager is transparent to the software object manager 18-27 which manipulates data and sends it to the high level feature. This is because there is a common information interface between the hardware object managers 18-37 and 18-41 and the analog input object manager 18-27. Thus, all hardware object managers communicate with the software object level 17-7 according to the same rules. Thus, the analog input object manager 18-27 can be written to deal with a generic object type, in this case, the analog input object. It need not contain alternative code for each single possible slave controller implementation of an analog input. It should be further noted that as shown in Figure 18, communication is possible between all the features and all the object managers in software 67 object level 18-7 and all the object managers in software object level 18- 7 and hardware object level 18-9. The actual communications paths used are a function only of the function performed by the feature and the data required. Thus, Feature y may also request software object Tl, thus accessing analog input object manager 18-27. Similarly, Feature n may request data from one or more object managers in software object level 18-7 which may further request data from one or more object managers in hardware object level 18-9. The commonality of interface between the hardware object and software object level simplifies the addition of new slave controllers and object instances. An object instance would be added in the above example if a fourth temperature sensor T4 were to be added to the system. A new slave controller of the same type would be added if a third type A slave controller, A3, were added. In both cases, all the necessary software exists on the network controller because there are no changes to the informational interfaces between the software object level 18-7 and the hardware object level 18-9. The user need only modify the database to create a new instance of the 18-29 analog input object T4 or the database 18- 39 to create another instance of type A controller object, e.g. A3, in the network controller. It is also possible to add a new slave controller type with minimal impact on the existing facilities management system software. Assume a new controller type, type C, is to be attached to the 68 local bus 17-13. This would require adding (by download or other means) a new hardware object manager to the existing software in the network controller acting as the master control node for operational units on that local bus. This hardware object manager would map the capabilities of the new controller into the software objects already defined in the system. For example, the new hardware controller may monitor analog temperature data in an unconventional manner, requiring a new hardware object manager. If the new controller produces analog temperature data, the new hardware object manager can map the data into a new instance T5 of the analog input objects. The existing software object managers and high level features in the software object level 17-7 and features level 17-5 of the network control software would be unaffected, since they would operate the same way as before. The only exception would be when the new hardware supports a new data type which is so different in operation from the existing types of objects that it could not be mapped into one of the existing software object managers at the software object level 17-7. In that case, a new software object might also have to be created. Thus, the hardware object managers have again been used to mask out the differences in the hardware to the software objects. Thus, the software object managers need not have different hardware dependent versions. A software object manager handles a data element the same way, whether 69 the data element comes from a sensor operated under type A control or another sensor operated under type B control. The hardware object managers format or map the data into the form required by the software object managers needs. This allows the software object managers to provide a hardware independent interface to the higher level software features. According to another aspect of the invention. Figure 19 illustrates that a software or hardware object manager provides a construct to handle data generated during a calculation in much the same way that data obtained directly from an operational unit such as a sensor is handled. According to the invention, a point is defined as a type of object. For example, an analog input point is a type of object. Therefore, the point has attributes such as its current value, high limit, low limit, alarm state, its hardware address, etc. These multiple dimensions to the point define the point as a vector quantity. A point is always associated with an operational unit such as a sensor in the field. Thus, operational unit 19-1 provides data to the network controller 19-3 which processes the data in a hardware object manager 19-5 into a form required by software object manager 19-7. The data corresponding to the point is stored as attributes 19-9 in a storage means, such as processor memory 17-4. Intermediate calculations at features level 19-11 sometimes require that the software object level 19-13 supply data which is not gathered 70 directly from an operational unit. In order to facilitate a common method of handling such data, pseudo points 19-15 are created at the software object level 19-13. A pseudo point is handled by software object manager 19-7 in exactly the same way as a point 19-9. The difference between a point and a pseudo point is that a point gets its values from operational units while a pseudo point obtains one or more of its attributes from an associated object. The pseudo point stores the identity of the associated object as one of its attributes. Thus, pseudo point 19-15 could recognize its associated object as point 19-9. In this case, pseudo point 19-15 could obtain one or more of its attributes from the attributes of point 19-9. This allows the software object manager 19-7 to treat all data requests from the features level 19-11 in the same way. Thus no distinction need be made between data obtained as points from operational units and other data used in intermediate calculations which is not directly obtained from such operational units. Figure 20 shows network controllers 20-1, 20- 3, 20-5 interconnected on high speed network bus 20- 7. High speed network bus 20-7 is used to transmit data among the nodes into computer 20-9. Computer 20-9 further transfers information to storage device 20-11 which contains archived data bases, such as archive data base 20-13 for network controller 20-1 and archive data base 20-15 for network controller 20-3. 71 Computer 20-9 contains generation software 20-10 which allows the user to create data elements at whatever level of data is appropriate to a specific application and to assign names to the data elements. Since no two elements may have the same name, the generation software checks the archived data bases or online databases and verifies that each data element is assigned its own unique name. When the name has been assigned, the name and the data element are both downloaded to the host node using high speed bus 20-7. This is shown generally in Figure 21 at generation time as reference numbers 21-20 and 21-22. As a result, the host nodes contain named data elements. As further shown in Function Block 21-24 in Figure 21, during run time a referencing node transmits a request for a data element by name. As shown in Function Block 21-26, if this is a first request for the named data element, the entire network is searched until the data element is found. This is shown generally in Function Block 21-28. As shown in Function Block 21-30, if the name cannot be found anywhere on the network, an error message 21- 32 is transmitted and the search for the name is terminated in Block 21-38. On the other hand, if the name is found, as shown in Function Block 21-34, the name is tagged with binding information. This binding information is a node address on the network and an internal address of the data element within the node's data base. The node address and internal address of the data element can have any convenient 72 format. In accordance with Function Block 21-36, the binding information and the data element itself are returned to the referencing node which stores the binding information. As shown in Block 21-26, if the referencing node is not making a first request for the data element, control passes to Function Block 21-40 where the binding information is read. Using the binding information, at Block 21-42 the name at the location specified (host node and data element location) is read and compared in Block 21-44 with the name requested. If the name found at the location specified matches the name requested, the data is returned to the requesting node in accordance with step 21-46 and the data acquisition routine is terminated. However, it is possible that the name found at the specified location does not match the name requested. This indicates that the binding information has become out of date. Typically the verification is done in the host node. The host verifies that the data requested is still at the same address by comparing the name passed with the name of the element stored at the bound address. As previously noted, if they are the same the binding is still valid and the data is returned as requested. However, if the data element has moved, either within the host node's data base or to another node, the host node detects the mismatch between the name now stored in that location in its data base and the name passed in the request. The 73 referencing node is informed that the binding information is out of date. The binding information can become out of date when a download, deletion, or other data base generation is performed on the host node, either deleting the data element or moving the data within the node to another location on the data base or moving the data to a different node. Any of these events can happen without the referencing node being informed. When the binding information is out of date, the referencing node executes a search of the network for the element name in accordance with step 21-28, again following the steps previously described for the first request of a data element name. If the data element name has been deleted, an error message 21-32 will be returned. However, if the data element name has been moved either within the node or to a different node, in accordance with steps 21-34 and 21-36, the name will be tagged with the new binding information. The new binding information and the data element will be returned to the referencing node. As a result of the above, the network is self healing. References which become out of date are corrected the first time a reference is made after the change of address has occurred. Further, if a referencing node is downloaded before a data element it references is downloaded, an error message is returned until the name is downloaded and then can be found. Thus, in accordance with the above invention, a search of the network need only be made either the first time the data element is requested 74 or the first time a data element is requested after it has been moved. Figure 22 illustrates a variation of the above described method. Figure 22-3 illustrates that after name generation 22-50 the names are downloaded at step 22-52 to the referencing nodes. At step 22-54, the referencing nodes create a name table. The reference table can be constructed to optimize memory usage in the node by keeping only one copy of the data element. All references and applications in a referencing node which require the data element are then replaced by a reference table index which typically requires fewer data bytes than an ASCII name. Thus, the name is kept in only one place, the reference table entry, as shown in steps 22-54 and 22-56 of Figure 22. It should be noted that in this method each referencing node keeps its own name table. Thus, after step 22-58 when the referencing node requests the data element, step 22-60 is executed to determine if this is the first request by the referencing node. If it is the first request by the referencing node, steps 22-62 through 22-72 in Figure 22 would be executed. This would involve searching the network for the element name, if the name is found returning the binding information and the data, and placing it in the table created in the referencing node as shown in step 22-72. Errors would be treated as previously discussed. If this is not the first request by the referencing node, then at step 22-74 the location of 75 the data element is read from the name table and the request sent to the host. The name is then compared by the host node with the name at the location specified in the name table. Based on the result of the comparison at step 22-78, the data will be returned to the requesting node or the network will be searched for the element name. It is important to note that within the referencing node, it does not matter in what application or feature the request for the data element originates. Once the binding occurs for one reference to that element, it occurs for all references in that node to that element. This means that the binding needs to occur only once for all references in the node instead of once for each place the reference occurs in the node. This reduces the time spent making initial bindings for all of the references by the node. It should be further noted that a separate reference table is built for each node. Thus, if the location of the data element is changed within the host node or to another host node, the process of updating the reference table will be repeated by each referencing node the first time that node requests the data element. Figure 23 shows a further optimization of the arrangement shown in Figure 22. Assuming a node has made a first request for a data element, the name of the location identified by the binding information is compared with the name of the data element currently being requested. In this case, if no match occurs, a local search is first performed at 76 step 23-82 by searching the host identified by the binding information. This is because it is likely that the data element will be found within the same host. If this is the case, control passes to step 23-70 where the binding information and data are returned to the referencing node. However, if this is not the case, the remainder of the network is searched beginning at step 23-62. A further embodiment avoids searching the network for references to data elements where the data element is stored in the same node as the requesting node (i.e., the host node and the referencing node are the same node) . As previously described, the reference name table must contain an entry for each name in the referencing node. This is necessary even if the referencing and host nodes are the same because the data may at some time move from this node to another node. Thus, it is not possible to eliminate an entry from the name table in the reference node even though the referencing node is also the host node for the named element. However, in these situations only, it is possible to eliminate searching the network the first time the referencing node requests a data item for which the referencing node is also the host node. This is achieved by having the data base software and the host node add the reference table entry when the element is downloaded. The table entry contains the correct binding information since the host node owns the data element and, hence, knows the binding. When the first reference from somewhere else on the 77 same node occurs, the binding information is already in the reference table and no additional searching is required. Thus, it is advantageous for a data element which is used frequently by a reference node to be hosted on that reference node. Figure 24 shows a further optimization technique using multiple levels of names. As illustrated, two levels of names are shown. However, the technique can be extended to an arbitrary depth of the naming hierarchy. Thus, small and hyphenated levels of names can be used. At each level a directory is formed permitting access to the next higher level. In a two level naming scheme, each name consists of two parts - a group name and an element name within the group. Each group is assigned to one node in the network and may have many elements within the group. A first directory or group directory, is a directory of all the groups in the network. The directory lists the name of each group and defines the node on which the group resides. Since the group directory must be kept on each node of the network, it is broadcast to all nodes in the network. The addition or deletion of groups must also be broadcasted to all nodes in the network so that they maintain an updated copy of the group directory. For each group on a node, the node contains a second level of directory called the element directory. The element directory lists all the elements in that group and identifies the node address of each element in the group. It is important to note that the elements in 78 the group need not reside on the node containing the group or element directory, nor need all the elements and the group reside on the same node of the network. Of course, the element directory is updated whenever an element is added or deleted from the group or moved from one node to another. Figure 24 illustrates how the directories are used. As shown in step 24-100, it is first determined if a reference node is making its first request for a data element. If this is a first request, in step 24-102 the reference node compares the group name to the group directory and identifies the group node. In step 24-104 if a match has not occurred error 24- 106 is indicated and the sequence of events is terminated. Assuming proper operation at step 24-104, a match occurs and at step 24-108 the request is sent to the group node as identified in the group directory. In step 24-110 at the group node, the element directory is searched to determine if the element appears in that group. Since the element directory contains the location of the data element, if a match occurred at step 24-112 then at step 24- 114 the group node reads the host node address from the element directory and at step 24-116 transfers the request to the host node. At step 24-118 the host node obtains the data and returns the binding information and the data to the reference node. Thus, the initial search for the name of the element is shortened to a search of the group directory followed by a search of the element directory for 79 the correct group. The entire network need not be searched. However, it should be noted that the directories must be kept up to date and that a copy of the group directory must be maintained on each node of the network. The group's element directory need be maintained only on the node where the group directory resides. The added bookkeeping is only required when a group or element is added or deleted or an element is moved. This is considerably less work than downloading all referencing nodes when such changes occur. The actual references of the software of the referencing nodes need not be affected. As previously discussed, if this is not a first request for data, binding information is read and the name is compared with the name found at the location identified by the binding information. If a match does not occur, then the binding information is no longer up to date and the sequence must again be executed to locate the proper information. In one application, the above described methods can be carried out in a facilities management system. This application to a facilities management system is by way of example and is not intended to be a limitation of the invention. In Figure 20 several real time network controllers and a personal computer used to generate data bases to download to the network controllers are interconnected on network 20-7. Storage means 20- 11, such as a disk attached to personal computer 20- 9 contains the data bases to be downloaded to 80 network controllers 20-1, 20-3 and 20-5. Each network controller and the personal computer can be considered a node. Assume NC2 is the name of a host node 3 and the host node owns a data object or element called AHU1/FAN. The system/object name is a two level naming scheme where the system name is the same as the group name in the above description and the object name is the name of the particular data object or element. This object is the return fan for air handler #1. It is a binary output object because it can be controlled to one of two positions and its name is unique on the network. The "group" or system name is AHUl and the "element" or object is FAN. Assume also that NCI is the name of node 1 and is a referencing node. This means it has several software features which need to reference the FAN object. As shown in Figure 20 Feature A needs to read the current value of the FAN object and Feature B sends a command to the FAN object to physically start the fan. As shown in the figures, a list of all the system names, group directories 20-200, 20- 202, and 20-204 is duplicated in each node. The group directories identify which node contains the directory of objects for a particular system. For the case of the AHUl system, the directory of objects is maintained by NC2 node 20-3. Thus, NC2, node 20-3, also contains a directory of objects in the AHUl system and where they are located in the data base. Similarly, the objects for the AHU2 system are located on NC3 or node 20-5. 81 As previously discussed, using personal computer 20-9, the user creates a data base which can be placed on archived files 20-13, 20-15 on storage disk 20-11 and can be downloaded to network controllers 20-1, 20-3 and 20-5. References, such as those from Features A and B to object AHUl/FAN, are kept in an ASCII name form when downloaded. This is because they are not yet bound at the time the data base for the network controller is downloaded. The referencing software features are oblivious to the actual physical location of the data object AHUl/FAN. Upon downloading, an object is given to a data base manager which manages all objects of the same type. In the case of AHU1/FAN, the binary output manager in NC2 is used. The object data base manager software initially enters the names into the reference name table. For example, when the binary output object manager is given the FAN object at download time, it places the FAN object into its own binary output data base and adds an entry in the reference table 20-300. This entry contains the name of the AHU1/FAN object and its binding information; object type (binary output) , host node address (NC2) , and data base location in the binary output data base (record 3) . In this example, the table entry is located at offset 16 as shown in Figure 20. Note that no other nodes besides NC2 know the binding information at this time. These nodes still only have a name reference to AHU1/FAN. The directory of objects and AHUl will later also 82 point to the reference table for the FAN object so that later lookups of the name will find it in the proper place. Data base for the referencing node 20-1, NCI, is also downloaded. This causes entries to be made in the reference table for NCI. When the data base for Feature A is downloaded, an entry is made into the reference table for AHU1/FAN but without the binding information. This "unbound" reference simply shows that some feature in NCI will be referencing FAN. When the data base for high level software Feature B is downloaded, it will also try to add the unbound reference to the table and find that it is already there (at offset 27 in the reference table 20-302) . Both features will then replace the named reference to AHU1/FAN with the offset of 27 into the table. Note that at this point in time the binding information is still not in the table in NCI. Execution of high level software Feature A in NCI requires reading the value of FAN object. Since the binding is not yet in the reference table in NCI for AHUl/FAN, the software must locate AHUl/FAN on the network. This requires searching the system name list or group directory in NCI for the system name AHUl. As shown in Figure 20, the list shows that AHUl is located on NC2. Thus, the software directs the request to NC2. NC2 locates the object in its data base using the element directory. This is accomplished by looking up FAN in the directory of objects in AHUl. In the example shown in Figure 20, this is a binary output point located at offset 83 16 in the reference table in NC2. The reference table of NC2 already has the binding information added for FAN, since this information was put there at download time, as described above. Hence, the software can send the request to the correct data base manager (binary output) object manager on this node and request the correct record, which is record 3. Once the data is obtained, the information is passed back to Feature A and NCI along with the binding information. At that time, the reference table entry for FAN is completed in node NCI with the correct binding information. Figure 20 also illustrates that for references in the host node, such as from Feature C in NC2, the binding information is already in the reference table after the data base is downloaded. Thus, the binding procedure is not required for those references, even the first time the reference is accessed. Since the binding information has been provided to network controller NCI, subsequent references from network controller NCI need not repeat the above procedure. Assuming Feature B needs to reference FAN, it uses the stored offset of 27 to find FAN in the reference table. This time the binding information is already in the table. Thus, the software could send a request directly to the binary output data base manager on node NC2 and request record 3. The look-up procedure described above is no longer required. Any other features on 84 NCI that subsequently reference FAN will use the same bound reference in the table, so the binding is only required once for all references from NCI. As previously discussed, the reference table reduces memory requirements since the longer ASCII name is replaced by a short table offset in each software feature and since only one table entry is required for all references from that same node. Figure 25 illustrates the sequence of events when a data element moves within a node. Assume that FAN moves within the data base of NC2 from record 3 to record 5. This could occur, for example, as a result of a data base regeneration on the personal computer so that record 3 is now an object called AHU1/PUMP while AHU1/FAN has been moved to record 5. The binding information used by network controller 25-1 to go directly to the binary output data base manager on network controller 25-2 would cause a request for record 3. However, the request also sends the name of AHU1/FAN so that it can be compared with the name found at record 3. In this case, the records no longer match. Using one of the optimizations described earlier, the binary output data base manager searches its own data base to see if it still has the object AHUl/FAN. In this case it is found at record 5, so the information requested is returned along with the new correct binding information. NCI sees that the binding it was using has been corrected by NC2 and updates its reference table by replacing the reference to record 3 with record 5. 85 Thus, the object has moved within network controller NC2, but network controller NCI was still able to find the data without any changes to the network controller NCI. Furthermore, all references in network controller 25-1 are corrected, since the common reference table entry is updated. Figure 26 illustrates the situation when, as a result of a download, a data object has been moved to a different network controller. In this case, the user has generated a data base for NC2 and NC3 moving the system or "group" name AHUl and its objects to NC3. Now, FAN is record 7 in the binary output data base on network controller NC3 (node 5) . Here, a network controller NCI attempt to reference FAN using the binding information it already has fails. This is because the name comparison at network controller NC2, record 3 shows that the AHUl/FAN data object is no longer at that address. Moreover, a check of the remaining elements in the NC2 data base shows that FAN cannot be found. Thus, Feature A in the network controller 1 receives an error message. Network controller 26-1 responds by erasing the binding information from its table and following the method discussed above to find the new location of AHUl/FAN. In this case it would be found on network controller 3 at record 7. Doing this once corrects all references in network controller NCI, since the common reference table is updated. 86 It should be noted that had the data element been completely deleted from the network, network controller NCI would have reported its inability to find FAN via an advisory message to an operator. This is also true for all references to FAN from NCI until FAN is downloaded again. Thus, an error occurs until AHUl/FAN is redefined, or the reference is removed. However, after the download the references will bind and begin to work properly. Hence, the order of node download is not critical. In order to provide proper time synchronization among nodes interconnected on an Nl bus, it is necessary for one of the nodes to play a limited system manager role. As shown in Figure 27, a node 27-1 is selected as a time synchronizer (a limited system manager) and at 27-2 the node defines the time and transmits this information to the other nodes interconnected on the Nl bus. Shown in 27-3, the nodes monitor the time during the non-update interval. Decision block 27-4 tests a clock to determine if it is currently the time for which resynchronization has been set. If not, control is transferred back to 27-3 and time monitoring continues. If it is determined in decision block 27-4 that it is now time to reestablish synchronization of time among the nodes, in block 27-5 the node tests to determine if it is the system time manager. If so, control is transferred to block 27-2 and the system time manager transmits the current time. If in decision block 27-5 the node recognizes it is not the system manager, in block 27-6 the node determines if it has received the time synchronization data. If so, the node resets its time in block 27-7 and time monitoring continues as in block 27-3. If the time synchronization data is not received at block 27-6, the node in block 27-8 determines if it can be the system time manager and, if so, transmits the time as in block 27-2. This allows a new node to assume the time synchronization responsibility if the original system time manager fails or goes off line. In addition to synchronizing time among the nodes, it is also necessary to synchronize global data. Figure 28 shows the fundamental steps in the download. In function block 28-1 a global data base is defined and loaded onto the network. A global data base can include such items as passwords, a list of system names (although not object names) , a list of nodes and printers on the system, report groups which indicate where user advisory messages of certain classifications are to be directed, and other information which would be useful to all the nodes. Function block 28-3 shows that each node also has a data base defined for it in an archive device. The node data base includes data to be stored in the node and additional data to be transmitted along the N2 bus to other devices controlled by the node. In function block 28-5, a node is configured on a network by giving it an Nl address and storing the identity of its archive 88 device in non-volatile memory. Following power-up at step 28-7, the node must be synchronized with the other nodes at step 28-9. Step 28-11 tests if the synchronization is complete. If not, control is transferred back to function block 28-9 to complete the synchronization process. Upon completion of node synchronization, control transfers to function block 28-13 in which the node accesses the archive device to download its own particular data base. As each data element is received, decision block 28-15 tests if the information is to be transmitted to a device on the N2 bus. If not, the information is stored in the node as shown in function block 28-17. If the information is destined for a device on the N2 network, as shown in function block 28-19 the information is passed onto the device through the N2 network. Figure 29 further illustrates how synchronization takes place. Upon power up, a node executes code in electronically programmable read only memory to identify the node's archive device defined in the non-volatile memory section of the node. This is shown in function block 29-1. As shown in function block 29-3, the node then requests the archive device to download the code into its random access memory. At decision block 29-5, the node joining the network tests to see if it has received a broadcast from another node on the network. According to the invention, the nodes on the network all periodically broadcast a time stamp indicating the latest version of the global data 89 base in that node. Thus, if a node joining a network has not yet received a broadcast time stamp as shown in decision block 25-9, the node waits until it does receive one. Upon receipt of the first broadcast time stamp, the node entering the network requests the global data from the node associated with the time stamp, as shown in function block 29-7. In addition, the new node stores the time it received with the global data base information as its time stamp. Subsequently, in function block 29-9, the node accesses the archive device to obtain its own particular data base, as previously discussed. After receiving its data base, the new node joins the others in the network in broadcasting its time stamp, as shown in function block 29-11. Synchronization of the data bases is maintained by receiving time stamps from other nodes as shown in function block 29-13. In the event that the time stamp received is later than the time stamp currently in the node, the node requests the global data from the node with a later time stamp, as shown in function blocks 29-15 and 29-17. It should also be noted, that it is possible for a node to become hung up waiting for global data which is not available. Thus waiting step 29-19 is tested against time expiration decision point 29-21. If a time has expired, then to avoid suspending operation of the node, the node accesses the archive device for the global data as shown in step 29-23. An alternative approach allows a node joining a network to avoid waiting for receipt of its first 90 time stamp, as described above. According to this alternative, the node joining the network first accesses the archive device for the global data and records the time stamp of the global data on the archive device as its time stamp. The node then joins the network, periodically transmitting its time stamp and examining time stamps of other nodes as described above. A similar approach is used with slave devices controlled by nodes on the N2 network. Every time an N2 device comes on line, it reports its data base revision level as a time stamp to its network controller. If the network controller has a new data base as indicated by its own time stamp, it downloads that information, which is some portion of the data base, to the device coming on line on the N2 network. If the network controller does not have a more recent data base than that indicated by the time stamp of the device operating on the N2 network, the network controller assumes that the N2 device has the correct data base. Figure 30 shows an approach to downloading information into a device without a routing table. The approach consists of cascading devices so that a path to a device without a routing table can be established through other devices which have routing tables. This is particularly useful in cases where it is not desirable to require personnel to go to an actual site of a device to physically download or upload a device's data base. According to the invention, each requesting network controller 91 maintains at a minimum in non-volatile memory the address of its archiving device. In addition, each network controller maintains in non-volatile memory the address of a network controller that will initiate a download on its behalf. This is called the NC initiator. The NC initiator must be initialized in a consistent state before it can facilitate a download/upload request from another node. Thus, a cascading mechanism is employed whereby nodes above in the hierarchy are initialized before nodes lower in the hierarchy are initialized. Two cases are possible. In Figure 30, download device 30-1 could initiate the download with network controller 3, shown as node 30-4 which does not have a routing table. Table 1 of Figure 31 shows the sequence of steps which are implemented by the network control layer of the archiving device or PC. It should be noted that each node is given an address defining its network, a local address on the network, and a port of the node. The node itself is assigned port 0. Thus, download device 30-1 has address 1:1:0. This is because the device is on network 1, local address l, and because a device itself is defined as port 0. As Table 1 at Figure 31 shows, the source of the message is 1:1:0, its destination is 2:4:0. An interim source of the message as it navigates the network is also shown. For the originator, the source and interim source are defined to be the same. Thus, the first interim source is 1:1:0. The remaining interim source entries in the table in Figure 31 have the same 92 network and local address as the preceding entry. A routing defined in a network layer such as that of the Open Systems Interconnetion model of International Standards Organization of the node routes the message to NCI which is network 1, local address 2, port 0. Tracing the steps through the table shows that by routing the message first through NCI and then NC2 the download information eventually arrives at NC3. NC3 replies to the source acknowledging the receipt of the message. Since the receiving device does not have a routing table, it replies to the node from which it received the message. From there, the acknowledgement could be routed over the same path as the message transmission in reverse direction or over any other convenient path defined by the nodes having routing tables. In the second case, network controller 3 initiates the download request to the archive PC 30- 1. In this case, node NC3 located at address 2:4:0 does not have a routing table to use for sending its download request. However, as previously mentioned NC3 maintains in non-volatile memory an address of a network controller that will initiate a download on its behalf. Thus, NC3 routes its request to this NC initiator. NC3 requests the download from the data download device at address 1:1:0, which is identified in NC3 as its archiving device. The route taken by the request, as shown in Table 2 in Figure 32, assumes that NC2 at address 2:3:0 is the NC initiator for NC3. NC2 must already contain a 93 routing table to send the message to the archive device. This illustrates that by cascading the devices the message can be received by the archiving PC. It should be noted that this creates a hierarchy of nodes such that a higher level node, such as NC2, must be fully functional before a lower order node, such as NC3 can be downloaded. Similarly if another node named NC3 as its NC initiator downloads to that other node could not take place until NC3 completed its download through its initiator, NC2. When downloads occur problems can result from objects whose system definition lies on a different NC than the object resides on. This is because two NCs cannot always be guaranteed to have mutually consistent data bases. These inconsistencies can not be automatically corrected, since they will naturally arise when several NCs have been affected whose definitions interlace. While these NCs are being updated (downloaded) there will necessarily be a time period during which inconsistencies cannot be avoided. However, all problem cases can be detected and reported to the user. When one NC is downloaded the others may be temporarily inconsistent with it. If this condition persists, or if the system attempts to access objects on either NC during this period of time, errors or ambiguities can occur. The following example demonstrates problems which can arise when an object is moved from one NC to another. Other scenarios could be constructed 94 but the data base inconsistencies resulting would be the same. The following assumptions are made: a. NCI contains the directory for system S. b. NC2 contains the original version of an object 0. c. NC3 contains the new version of the same object 0. The normal case is to add object 0 to the data base for NC3 and delete it from NC2. This can be done either through template generation (single object changes) or via DDL (data definition language) . In either case inconsistencies can occur. Assume DDL is used for this change. Then three NC DDL files need to be updated (NCs 1, 2, and 3) in order to complete the transaction. Each of the NCs must then be downloaded. However, one or more of the downloads could be skipped or an old data base incorrectly downloaded, resulting in inconsistent NCs in the field. Similar problems can occur if a template generation change fails or is cut off in the middle for some reason. The following cases demonstrate the inconsistencies which can arise. Assume that, after the above changes have been made, NCI is downloaded first. Then the system directory for S will indicate that object O should reside on NC3. Until NC3 is downloaded (if it ever is!) object O can not be found, since the directory says it should be on NC3. This is the first problem case - a directory pointing to an object which is 95 not there. Note that bound references will continue to use the old object 0 in NC2 for now. New bindings can not be accomplished since the directory is needed for new bindings and it points to a non- existent object. Further assume that NC2 is downloaded next. This creates the same problem as above with the additional problem that even old bindings will fail, since the old version of object 0 is now deleted. Until NC3 is downloaded the object does not exist. Now suppose NC2 is downloaded first. This is again the same problem, since the old directory for S still points to NC2 which no longer contains the object. Current bindings become invalid and new bindings can not be made. After NC2 is downloaded, further assume NCI is downloaded second. Same problem again occurs, since the directory points to NC3 which has not been downloaded with the new object yet and the old object is gone. Now assume NC3 is downloaded first. As a result of this download, there are two copies of object O in the field. This demonstrates a second problem which can arise - duplicate objects with the same name in multiple NCs. Old name bindings previously discussed will continue to use the old version of 0 in NC2. New bindings will also go to NC2 since the directory is still not updated. Until NCI is downloaded, the new version of 0 is inaccessible. This is referred to as an "orphan object" - it cannot be accessed, since its name is in no directory. There is no way for the user to 96 examine, change, or even delete this version of the object. This demonstrates that a third problem can arise. After NC3 is downloaded, further assume NCI is downloaded. Now there are still duplicate objects 0 but features can be bound to BOTH copies of 0. Old bindings to 0 are still valid, since the object can still be found on NC2 but new bindings will go to NC3 since the new object is in the directory. Thus, for example, event triggers which cause high level features to refocus certain tasks, as discussed below, could be signed-up and received from both copies at the same time. If the object type of 0 has not changed, then both triggers will be considered valid by the receiving task. This is a variation of problem two (duplicate objects) - now binding can be made to both versions. Other scenarios result in the same problems. That is, downloading NC2 then NC3 or vice versa results in a directory in NCI pointing to a non-existent object in NC2 and an orphan object in NC3. In summary, then, the following problems can occur after downloading: a. A directory in a node can point to a non-existent object. b. Orphan objects cannot be accessed or removed - no directory points to the object; and c. Duplicate objects can occur and binding can be to either copy of the object. These downloading problems can not be automatically corrected, since the software can not 97 know where in the order of download the user is - i.e., it can not determine what the NC data bases should look like now or when the downloads are completed. However, the problem can be detected and the operator alerted as follows. Assume the following definitions: Directory NC - the NC or node containing the directory for system S. Object NC - the NC or node containing an object in system S. "Here I am" message - a message which is sent by an object to its directory NC signifying that the object exists, where it is found and its type. "Are you there" message - a message which is sent by a directory to one of its objects requesting the object respond (to determine if the object is on the correct NC and is the correct type) . Since inconsistencies normally arise out of download, the following scenarios would catch the above errors as they are introduced. The object NC sees its directory NC come online - in this case the NCs could be out of synch, since one could have had changes made while the other was off-line. Thus, it is necessary to resynchronize the directories. This is done by each object whose directory is in the NC which came online (as defined by the global system directory data base) sending a "Here I am" message to its directory NC. This catches two of the problems. First, it catches orphan objects, since 98 the directory NC will not find the object in its directory. It can then report an error to the user. Second, it catches duplicate objects since both try to report to the same directory. However, one must be an orphan since the directory can only point to one of them at a time. Again an error can be sent by the directory manager of the directory NC to the user. A check could also be made on the object type to guarantee that the object reporting in is the proper object type as determined by the directory. In a second case, the directory NC sees the object NC come online. In this case sending an "Are you there" message from the directory to its objects checks for the existence of the objects. This catches the errors in which a directory points to a non-existent object, since the object does not respond if it is not there. Again, object types could also be cross-checked. In a third case, the directory NC sees the object NC (or vice versa) go off-line. Little can be done here until communications between the two can be established. In a fourth case, the object NC sees the directory NC downloaded. This is treated the same as the online case. The objects send the "here I am" message to determine if the download changed anything. In a fifth case, the directory NC sees the object NC downloaded. This is the same as the second case. The "Are you there" message is sent to determine if the object is still there. 99 In summary, the "Here I am" message is used to catch duplicate and orphan objects at those times when the relationship between the directory and object NC may or may not be used. The "Are you there" message catches non-existent objects, since these will be caught by the references when they occur. A directory manager task in the node is responsible for performing both halves of the solution. The directory manager task maintains a Reference Identification (RID) table. Thus, it knows all objects that are defined on the NC and can run through this list when a directory NC comes online, etc. It sends the "Here I am" messages for all objects whose system is on that other NC. If necessary, it can run through the directories it owns and send the "Are you there" messages to all objects defined to reside on that other NC. In addition, the directory manager receives both of these messages on the other end. The "here I am" is sent to the directory manager which checks its directory to ensure that the object is supposed to be where it is. The "Are you there" message also goes to the directory manager of the object NC who looks in the RID table for that object. This linkage checking need only be done when the system and object lie on different NCs. The inconsistencies are not possible within a single NC. If they exist, it is due to a template generation transaction which was interrupted. In that case, the user can be made aware that a problem exists, 100 since an error can be issued at the time the transaction was interrupted. The way in which one NC sees that another is online, downloaded, etc. is done the same as for trigger handling. The node status message is sent to the node manager which distributes it to the directory manager after which the above processing can occur. Error messages are inevitable when a point and its system are on different NCs, since one NC must be downloaded before the other. This will happen even if the user conscientiously downloads all the affected NCs. However, the number of such cases (split object and directory) typically is few and this will most likely occur only when an object is moved from one NC to another. In a facilities management system, it is preferable to replace polling type applications where a needed data value is repeatedly read at some interval with an event based scheme which only executes an algorithm when a value changes. This requires recognizing when data has changed and associating the change of data with a triggerable object or feature. In a distributed environment, it must be recognized that the owner and user of the data may be in separate nodes or processors, as data bases may be changed independently of each other. Introducing a sign-up mechanism allows a feature needing specific data to request the node containing the specific data or data element to inform the feature whenever the specific data or data element 101 changes. As a result, polling is no longer required. However, in a distributed environment, a node containing the specified data may experience a download of a new data base resulting in a loss of the sign-up request. The same problem occurs if the data moves from one network node to another. Thus, if a node is updated by data base generation or download, the signing up feature must be informed. As previously discussed, each node periodically transmits a time stamp indicating its most recent data. Thus, if a node has been detected to go off line or to have been downloaded with new data, the sign-up feature will invalidate its sign-up and attempt a new sign-up with the new data base. If this is not possible, the binding scheme previously discussed allows the signing up feature to determine where the data has now been located. If the data is no longer available, of course, sign-ups are not possible. It should be noted that trigger sign-ups can be used to drive several features including event totalization or a customized feature programmed by the user. Similarly, sign-ups could also be used to drive the refreshing of person machine interface screens rather than interval refreshing of such screens. This would allow immediate notification to a user of changes in the state of the variable or data. Figure 33 illustrates the process. As shown in block 33-1 features sign up for triggering by objects which are named data elements in the system. 102 In block 33-2, a processor in the node checks if the object is present on the network. As shown in block 33-3 if not, the feature begins monitoring the network to determine if a new network controller (NC) becomes added. When a new NC is detected as shown in block 33-4, the feature checks the new NC for the triggerable object and repeats the processing in block 33-2. When a feature determines the object is present, then the feature tests to determine if new data was downloaded with the object in an NC, as shown in block 33-5. If this is the case, the feature repeats its sign up in block 33-1. Otherwise, as shown in block 33-6 the feature monitors the triggerable attribute of the object. Block 33-7 shows that changes to the attribute's status sends a trigger to the feature (block 33-8) . Whether or not the feature receives the trigger, the feature repeats processing beginning at block 33-5. This allows the feature to recognize downloads of new data to the node having the object so that it can again sign up to be triggered. By repeating step 33-2, the feature can pick up triggerable objects which have been relocated in the network. According to the invention, global data in the network controllers identify the destinations of various reports created during system processing. A system produces several types of reports with unique lists of targets. For example, reports can be of the critical type (1-4) maintenance (follow- up) , and status. In addition, point history -1 03- reports, totalization reports, trend reports, and transaction log or trace reports are created. Another requirement is that all critical type reports in a facilities management system be preserved until delivered to at least one of the targets defined for the report type. In order to facilitate report routing, all reports emanating from a given node are routed to a specially designed report router task for ultimate distribution to various hard copy devices, computer files, and other storage devices. As shown in Figure 34, if point 34-1 changes, a message is sent to report router 34- 3 in network controller 34-5 through communications task 34-23. Report router 34-3 determines that the message should be sent to its preferred destination, printer 34-7, which is under the control of network controller 34-9. This is accomplished by report router 34-3 sending the change of state information to I/O task 34-11. Report router 34-3 also keeps a copy of the message. If printer 34-7 prints the message, notification is sent back to report router 34-3 and the copy is deleted. On the other hand, if printer 34-7 is off¬ line or for some other reason cannot print the message, I/O task 34-11 notifies report router 34- 13, which is the report router available in the same network controller as the destination printer. If report router 34-13 is unable to locate a default device, the message is discarded. Report router 34- 3 receives no message from report routers 34-11 or 34-13 and therefore report router 34-3 indicates SUBSTITUTE SHEET, -1 04 - that the information has not been stored or printed by not indicating a change of state. The report router 34-3 then maintains its copy of the message. On the other hand, if report router 34-13 locates a default device, such as printer 34-15 connected to network controller 34-17 to report router 34-19, report router 34-13 routes the message to 10 task 34-21 for transmission to printer 34-15. If the default device also does not operate, the message is discarded and no message is returned to report router 34-3 indicating that the report has been neither printed nor stored. Report router 34-3 then keeps a copy of the message in its save file. If a printer comes on-line, all report routers are notified. If the save file contains a message, the message is routed to the specified device again. Should the save file be filled, the lowest priority and oldest message is removed from the save file and an error is logged on the system. Figures 35 and 36 illustrate distributed filter processing for generating report summaries. Report summaries are generated based on an object name and certain selection criteria. One approach is to have the remote device which is to receive the summary retrieve each object directory and then retrieve a record for each object identified in the directory. The remote device then keeps only those records which meet the criteria for the summary. However, this would require a significant amount of processing and communication among nodes. Thus, localized filtering, e.g., filter task 35-11, of the SUBSTITUTESHEET -104a- data at the node at which SUBS TITUTESHEET 105 the particular object directory of interest is located is desireable. As shown in Figure 35, feature 35-1 and node 35-3 may require transmitting a data summary to PC 35-5. However, the objects required to construct the summary may be scattered throughout the system. The object directory is directory 35-7 located in NC2, shown at 35-9. As shown in Figure 36, feature 35-1 generates a directive specifying an object name and selection criteria in function block 36-1. In function block 36-5, the object directory 35-7 is located in network controller 2 shown at 35-9. At step 36-3, the object directory is read from the node location and the number of records and attributes with the same system and object name is recorded. Using the object directory 35-7 the objects are retrieved from network control nodes in NCI, NC2, NC3, and NC4. When the objects are retrieved, in step 36-9 the selection criteria included in the directive generated in step 36-1 are applied. As indicated in step 36-11, if the criteria is not met, the element is discarded, while if the criteria is met in the function block 36-13 the attribute is stored in the message buffer. Decision block 36-15 tests whether all the attributes have been evaluated. If not the selection criteria is applied to the next attribute. If all the attributes have been evaluated, a message is generated to send a single message to the requesting node 35-1 in the form of a message block with the attributes requested. 106 For purposes of illustration, system 1 in Figure 37 can be a facilities management system (FMS) having nodes 37-3, 37-5, 37-9 and 37-11 which function as network controllers to process data related to building and industrial, environmental, security and other automated system controls. As illustrative node 37-3 shows, each such node or network controller has at least one processor 37-2, a memory 37-6, and equipment interface circuits 37- 8. Such equipment interface circuits may accommodate numerous equipment interconnection arrangements, including, but not limited to, interfaces which use direct and secondary communications links to the node. In operation, network controller 37-3 could be monitoring measurements from air flow sensor 37-10 and temperature sensor 37-12 and in response opening and closing dampers 37-14. It is understood however, that nothing limits the application of this invention to such FMS systems and that numerous types of networked systems can benefit from this invention. In the system 37-1, network controllers 37-3 and 37-5 are connected by a first communications link. The first communications link 37-4 is connected via gateway 37-7 to a second communications link 37-17 having network controllers 37-9 and 37-11 attached. The nodes attached to communications links 37-4 and 37-17 can be considered to form individual networks. The number of nodes or network controllers on a network and the 107 number of networks interconnected by gateways on a system is a function of systems requirements and capabilities. It is understood that the principles of the present invention apply to any number of nodes or network controllers on any number of communication links and are not limited in this respect. According to a routing convention in Figure 37, each node is identified by a network address. The elements of a network address include at least three fields: first, an identifier of the communication link called a subnet, and second, a local address of the node on the communications link or subnet. For example, node 37-9 is at subnet 2 local address 1. The third field of the network address is the port number of the node from which a device is dropped, called the Drop ID. As illustrated in Figure 37, each individual configured node itself is Drop ID 0. Non-configured devices, such as lap-top computers or other data processing devices, can be connected or dropped to numbered ports of the node. Here it is again understood that the present invention accommodates any number of node ports and introduces no limit on such node port capabilities. A port of non-configured lap-top computer 37-13 can be connected to a port from a node, such as node 37-3 and assigned a network address. For example, if port 2 of non-configured lap-top computer 37-13 is connected to port 3 (Drop ID 3) of node 3 which is at subnet 1, local address 1, the network address of lap-top 37-13 is 1:1:3 as 108 shown in Fig. 37. It should be noted that the port of lap-top computer 37-13 is not part of the network address. Figure 37 further illustrates that another lap-top computer 37-15 can be part of the network as originally configured. According to the naming convention, such devices are identified as additional nodes on additional subnets, in this case, subnet 3, local address 1, Drop ID 0. Finally, for convenience, the naming convention allows further appending an identifier of a process in the device, although this is not required. The only requirement is that the subnet, local address and the Drop ID be included in the fields of the network address. Such process identifiers identify the process in the device which is the source of the message and which will usually receive the response, and the process in the device which is the destination of the message and which will usually generate the response. It should be further understood that nodes or network controllers can be organized into any combination of processing layers such as network and data link layers from the open system interconnection architecture of the International Standards Organization or any other convenient architecture, as illustrated in Figure 38. According to the invention, when a non- configured device is attached to a port of a configured node, the non-configured device establishes its presence on the port. When receiving messages from other configured nodes the 109 configured node first determines from the subnet and local address destination portions of the message if it is the destination node. If not, the message is passed on to the next proper configured node defined by the route. At the destination, the configured node evaluates the Drop ID of the received messages to determine if the message is for itself (Drop ID 0) or for the attached-non-configured device (non¬ zero Drop ID) . Figure 39 illustrates the generation and transmission of a message by a process on non- configured lap-top 37-13 which seeks to communicate over the network with another device. To initiate the communication request shown in block 39-301 an initialization phase first takes place in which the non-configured device establishes its location on the network. Non-configured device 37-13 sends a message requesting the address of the node or FMS network controller to which it is attached, in this case node 3. The node or FMS network controller responds by activating an initialization task which sends the network address including the subnet, local address and Drop ID back to the non-configured device. The non-configured device then stores this information as its network address. In function block 39-303 the non-configured device accesses this address and uses it as the source address portion of messages it generates. These messages include both the source address and destination address and data or data requests to be transmitted. For illustration, assume that non- 110 configured lap-top 37-13 has requested data concerning the status of a damper 37-16 recorded in configured lap-top 37-15. In function block 39-305 the processor in the node transmitting the message determines if the request is for a process remotely located in another node or for a local process in this node. If not, as shown in function block 39- 307, the request is delivered to the local process and exit 39-309 is taken. If the request is for a process in another node, function block 39-311 determines if the source and destination network addresses are valid. This requires that network processing layer 38-201 in the node verify that the subnet, the local address of the node or network controller on the subnet, the Drop ID and the process identifier are valid. If not, error processing 39-313 begins and exit 39-309 is taken. If the network addresses are valid, the network layer 38-201 in the first node references a routing table stored in a memory 37-6; to determine the next hop in the path. As previously discussed, such routing tables may be static or dynamic, centralized or decentralized. For illustrative purposes only and not as a limitation of the invention, a static routing table is assumed. The request is then tagged with the network address of the transmitting node for acknowledgement by the next intermediate destination in the data link layer 38-203 of the node, as shown in function block 39-317. Transmission of the request then takes place in function block 39-319. 111 As discussed above, Figure 39 illustrates the activities involved following a request from a non- configured device to communicate over the network. The same processing takes place when a node or network controller transmits a response from a configured device. Thus, by using the same processing that takes place when a network controller or node transmits a response from a configured device, a request by a non-configured device to communicate over the network can be accommodated. Figures 37 and 38 and the table in Figure 41 show further detail in routing the request from the non-configured lap-top source 37-13 to the configured lap-top destination 37-15. Non- configured lap-top source 1:1:3:PIDX identifies a process on subnet 1, local address 1, Drop ID 3 identified as PIDX. The message from non-configured lap-top 37-13 also identifies the destination as subnet 3, local address 1, Drop ID 0, process PIDY. Thus, the first routing, which would not be defined in a routing table at configuration time, is from l:l:3:PIDX to 1:1:0. This represents the path between the non-configured lap-top 37-13 and the node or network controller 37-3. The static routing tables which were defined at configuration provide the routing from node or network controller 37-3, network address 1:1:0, to configured lap-top 37-15, network address 3:1:0. As shown in Figures 37, 39, and 41 the next stop from node 37-3 identified in the static routing table is to the network 1 side of 112 gateway 37-7 which is defined as subnet 1, local address location 4, Drop ID 0. The routing table in gateway 37-7 directs this request to the output of the gateway at subnet 2, local address 4 Drop ID 0. The routing table at the gateway determines that the efficient route for this request is directly to node 11 defined as subnet 2, local address 2, Drop ID 0. Node 37-11 has its own routing table which routes the message off port 3 to an address defined as subnet 3, local address 1, Drop ID 0. The message is then routed to the process identified as PIDY. Figure 38 illustrates the activities that take place in the network and data link layers at each intermediate stage of the process. As previously discussed, the intermediate receivers and senders of messages are determined by the entries in the static or dynamic routing tables in memory at each node. In the intermediate stages, a message is received and an acknowledge signal is transmitted by the data link layer 38-203 of the receiving configured node to the intermediate node which forwarded the message. The network layer 38-201 determines if the destination for the message is this configured node or some other configured node and finds the appropriate next intermediate destination from the routing table. The data link layer 38-203 retags the message for acknowledgement by the next intermediate stage and then transmits the message to the next intermediate destination identified by the network layer 38-201. 113 Figure 40 illustrates the activities of any given node which take place upon receipt of a request from a non-configured device. These activities are the same as those that take place upon the receipt of a response from a configured device. Thus, the same approach for handling receipt of responses from configured devices can be used to respond to a request from a non-configured device. As previously discussed, messages from configured nodes are tagged by the forwarding node so that receipt can be acknowledged. As shown in Figure 40, in function block 40-403 the message is first evaluated to determine if the tagged message is from a valid source to a valid destination and whether the message is appropriately tagged, as previously discussed relative to Figure 39. If not, as shown in function block 40-405, the message is discarded and an exit 40-407 is taken. In addition, other known tag functions for reliability such as sliding windows, can be performed. If the processing in the data link layer 38-203 in function block 40-403 identifies the message as valid, function block 40-409, also a part of the data link layer 38-203, transmits an acknowledgement of receipt of the message to the forwarding node. At the network layer 38-201, the message is tested in function block 40-411 to determine if the destination process is located at the receiving configured node. If so, function block 40-413 delivers the request to a process local to the receiving node and takes exit 40-407. If the 114 destination process is not located at this node, network layer 38-201 processing continues as shown in block 40-415. The destination process is then tested to determine if it is for a non-configured node. If this is the case, the network layer readdresses the response for a non-configured device, the data link layer retags the response and it is then transmitted, as shown in function blocks 40-417, 40-419 and 40-421 respectively. If the processing in block 40-415 is such that the destination process is not at a non-configuring node, the request is readdressed for the next hop in the path, retagged, and transmitted as shown in blocks 40-423, 40-425, and 40-427 respectively. It should be noted that processing in function blocks 40-409-427 is the same for receipt by any node in the system. Figure 41 shows that the response from configured lap-top 37-15 can be routed to non- configured lap-top 37-13 at network address 1:1:3 by retracing the exact message path previously traversed in going from non-configured lap-top 37-13 to configured lap-top 37-15. Using this approach, it is not necessary to actively evaluate an additional data communication path to return the information required by the non-configured device. The response from lap-top 37-15 containing the status of damper 37-16 is routed back through the nodes to node 37-3 which as previously discussed, tests the messages it receives to determine if the message is destined for the node itself or for the 115 non-configured device on the node. In this case lap-top 37-15 addresses the response to the source of the request, identified as network address 1:1:3. Since node 37-3 at subnet 1, local address 1 recognizes the Drop ID 3 as the node port attached to non-configured device 37-13, the response is sent to lap-top 37-13. Finally, it should be noted that a response from configured node 37-15 to the request from non- configured device 37-13 need not traverse the same path. For example, in adaptive routing systems variations in message traffic conditions may result in the response traversing a different path through the network than the request. Indeed, it is possible for the network on communications link 37-4 to employ a static routing scheme, while the network on communications link 37-17 employs an adaptive routing, or vice versa. All adaptive, all non- adaptive, or any combination of networks can be used with the invention. However, regardless of how the response reaches the configured node, the configured node routes the message to the non-configured device based on the Drop ID in the network address given as the destination of the message. As a result, functions which are not normally incorporated into the network can be performed by attaching a non- configured device to a convenient port from one of the nodes on one of the networks in the system. This is because the Drop ID of the network address allows responses from configured nodes to be routed 116 to non-configured devices dropped from ports on configured nodes. Figure 42 shows one possible configuration of a facilities management system using a network approach with multiple levels of control. Network controllers 42-1, 42-3 and 42-5 operate at a first level and communicate with each other over a high speed network bus 42-7. The number of network controllers which can be interconnected is limited only by the capabilities of the network controllers themselves and the high speed bus 42-7. Each of the controllers 41-1, 42-3 and 42-5 at this first level are peers because they have access to the same high speed network bus and operate to control other lower level functions. Figure 42 illustrates this principle at network controller 42-5. Network controller 42-5 operates as a master node relative to slave controllers 42-11, 42-13 and 42-15. The network controller 42-5 communicates with slave controllers 42-11, 42-13 and 42-15 over a local bus 42-9 and with other network controllers over high speed bus 42-7. As the master controller, network controller 42-5 allocates resources on the local bus among the slave controllers 42-11, 42-13 and 42-15. Each slave controller performs its individual functions and communicates with data acquisition units 42-17, 42-19 and 42-21, respectively. Data acquisition units connected to sensors provide information needed for the slave node to perform its data processing functions. 117 Certain functions in the slave nodes 42-11, 42-13 and 42-15 may require access to information obtained by data acquisition units not controlled by the particular slave node. For example, in performing its individualized function, slave node 42-11 may require access to information provided by sensors connected to data acquisition unit 42-19 which is controlled by slave controller 42-13. In order to obtain this data, the slave controller 42- 11 signals network controller 42-5 over the low speed bus 42-9. In traditional systems, network controller 42-5 then transmits a message over low speed bus 42-9 to slave controller 42-13 requesting the data. Slave controller 42-13 would then respond by transmitting the data to network controller 42-5 over the low speed bus 42-9. Network controller 42- 5 would then pass the required data to slave controller 42-11. As the above example illustrates, the request from slave controller 42-11 for data available from data acquisition units 42-19 results in a series of messages transmitted over the low speed bus. As the number of data access requests across slave controllers increases, the message traffic across the slow speed bus grows at a high rate resulting in data bus congestion and a reduction in processing efficiency. The situation is compounded by additional requests made from peer network control nodes over the high speed bus. For example, for network controller 42-3 to access data available from data 118 acquisition unit 42-19, a request must first be made to network controller 42-5 over high speed bus 42-7. Network controller 42-5 then communicates over local bus 42-9 in the manner described above. Thus, additional message traffic occurs both on the local low speed bus 42-9 and on high speed bus 42-7. In addition, if network controller 42-3 is making its request for data based on a request for data based on a lower level slave controller of its own, additional delays are incurred on the local bus connecting network controller 42-3 and its slave controllers. Thus, it is inefficient for each data request to generate a series of messages resulting in the actual data being obtained from the data acquisition unit controlling the particular sensor. An additional problem occurs when the network controller 42-5 itself requires access to multiple data items acquired by the data acquisition units 42-17, 42-19 and 42-21. A "feature" of a system, defined as a function performed by the system, often requires data from one or more sensors which may be at different locations in the system. When one feature implemented by a portion of the program in network controller 42-5 requires access to data available from a data acquisition unit, the network controller must seize control of the local bus and transmit a message to the appropriate slave controller to acquire the information and transmit the information back to the master controller. The slave controller responds by transmitting the requested information. This also results in 119 communication bottlenecks and reduced data processing efficiency. As a result, higher priority functions, such as fire alarm messages, become stacked in a waiting list delaying corrective action. Figure 43 shows one embodiment of the present invention. Network controller 43-23 is connected to high speed bus 43-25 and slave controllers 43-27, 43-29, 43-31 and 43-33 over local bus 43-35. As previously mentioned, any number of slave controllers can be connected to network controller 43-23 depending on the processing capabilities and requirements of the network controller and on the communication capabilities of the local bus. In figure 43, network controller 43-23 is shown having three representative features, 43-35, 43-37 and 43- 39. It is assumed that each of these features is carried out under the control of processor 43-41. The number of features shown is by way of illustration and is not intended as a limitation. It is further assumed that each of the features represents a desirable function requiring access to data available through the slave controllers and is carried out in network controller 43-23. Finally, Figure 43 shows a stored data table 43-43. The stored data table is a cache memory used to hold values of data items as they are received from the slave controller by the master controller. Aging timers 43-45 are associated with each data item received and represent a predetermined time during which an individual data item in stored data table 120 43-43 is valid. Thus, each data item in stored data table 43-43 is associated with its own aging timer 43-45. In operation, when a feature within the network controller or another processor or network controller requests data to perform a function, the network controller determines if the data is available in stored data table 43-43. If the data is present in the stored data table, the network controller then determines if the aging timer associated with the data has expired since the data was last acquired. If the aging timer has expired, the network controller then issues messages required to obtain new data from the appropriate processor and data acquisition unit. If the aging timer has not expired, network controller 23 provides the feature, or other processor with the most recent information available in the stored data table. As a result, it is assumed that no significant change in the value of the sensor has occurred. Assume that at t 0 Feature 1 represented by reference number 43-35 in Figure 43 requests data from a sensor controlled by slave controller 43-27. Network controller 43-23, under the control of processor 43-41, determines that there is no entry in stored data table 43-43. Thus, network controller 43-23 issues messages over the local bus to slave controller 43-27 directing slave controller 43-27 to obtain the information from a data acquisition unit and provide the information to network controller 43-23. When network controller 121 43-23 receives the data from slave controller 43-27, it stores the information in the stored data table and associates a predetermined aging timer with the data item stored. It should be noted that the aging timer can be implemented in any number of ways known in the art. For example, a count down clock could be set and counted down from the time the information is stored. This could be achieved by preloading a register to a known state and clocking the register up or down until a second logical state, e.g. all logical ones or logical zeros, is attained. Alternatively, the time of storage could be recorded and compared with the time at the next data access. In this case, we assume, for example, that the aging timer is set for 100 milliseconds. The selection of 100 milliseconds is based on predetermined system characteristics in which it is known that data acquired by this particular sensor will be valid for 100 milliseconds. At t 0 plus 50 milliseconds Feature 2 requests access to the same data. Under the control of processor 43-41, master controller 43-23 determines that the data item requested exists in stored data table 43-43. The master controller then tests the corresponding aging timer. Since data acquired at t 0 was valid for 100 milliseconds and since the data access in this case occurred only 50 milliseconds after the data was acquired, the data aging timer has not expired. Therefore network controller 43-23 will provide the data to be processed by Feature 2 from the stored data table. This is true even if 122 the sensor controlled by slave 43-27 has changed in value. The advantage is that no further data communication is required over the local bus for Feature 2 to have access to a valid value of the required parameter. At t 0 plus 100 milliseconds Feature 3 requests data available from a sensor controlled by slave controller 43-29. Since this data has not been recorded in the stored data table 43-43, network controller 43-23 issues the appropriate data communication messages to acquire the data. When network controller 43-23 receives the data from slave controller 43-29, the data is stored in the stored data table 43-43. At t 0 plus 150 milliseconds Feature 1 again requests access to the same data element obtained by slave controller 43-27 at t 0 . However, the processor in the network controller determines that the data aging timer has expired. Thus, network controller 43-23 issues messages to acquire fresh data through slave controller 43-27. Assuming network delays of 1 millisecond, the data is stored in the stored data table at t 0 plus 151 milliseconds. Since the data aging timer for this data is 100 milliseconds, the data will remain valid until t 0 plus 251 milliseconds. It should be noted that the stored data table was not updated at 100 milliseconds when the data aging timer for the data acquired at t 0 expired. Even though the value of the sensor data controlled by slave 27 may have changed by this time, no 123 feature or other processor required access to this data. Thus, it was not necessary to update the stored data table until access to the expired data was required. This further reduces unproductive communication on the local and high speed data buses. Another embodiment of the invention is shown in Figure 44. Figure 44 illustrates a further reduction in communication bottlenecks on a high speed network bus 44-50. Network controller 44-52 performs representative Features 44-53, 44-56 and 44-58 under the control of processor 44-60. Network controller 44-52 also contains data storage table 44-62 and aging timer 44-64 and is connected over local bus 44-65 to slave controllers 44-66, 44-68, 44-70 and 44-72. Such slave controllers generally may be connected to one or more sensors, S, or other devices. Similarly, network controller 44-54 performs Features 44-74 and 44-76 under the control of processor 44-78. Network controller 44-54 further includes data storage table 44-80 and aging timer 44-82 and communicates over local bus 44-83 with slave controllers 44-84, 44-86 and 44-88. By way of example, at time t 0 Feature 44-74 requests data available from a sensor controlled by slave controller 44-84. As previously discussed, network controller 44-54 generates appropriate messages over local bus 44-83 which causes slave controller 44-84 to acquire the data and transmit it to network controller 44-54. Network controller 44- 54 then stores the information in the stored data 124 table 44-80 and assigns a predetermined aging time value 44-82. At t 0 plus 30 milliseconds, a feature (44-53, 44-56, 44-58) in network controller 44-52 requests the same data over the high speed network bus 44-50. In response, network controller 44-54 determines from the data storage table 44-80 and the data aging timer 44-82 that the current value in the data storage table is valid and need not be updated. Thus, network controller 44-54 transmits over network bus 44-50 the requested data as found in the data storage table. In addition, network controller 44-54 transmits the time the data was read (the actual value of t 0 ) and the value of the aging timer. In response, network controller 44-52 stores the data received in its data storage table 44-62 and provides it to the requesting feature for processing. In addition, network controller 44-52 determines the time the data is stored in its data storage table 44-62 and how much longer the data will be valid based on the aging time transmitted by network controller 44-54. Assuming delays of approximately 2 milliseconds in transmitting data, the data is stored in data table 44-62 at t 0 plus 32 milliseconds. Since the data would be valid from t 0 to t 0 plus 100 milliseconds, network controller 52 determines that the data will be valid for an additional 68 milliseconds. Thus, network controller 44-52 stores an aging time value of 68 milliseconds as aging timer 44-64 corresponding to the data element obtained from network controller 44-54. Thus, for the next 68 milliseconds, the time 125 during which network controller 44-54 will not again access slave controller 44-84 to obtain this data, features in network controller 44-52 or slave controllers connected to network controller 44-52 over local bus 44-65 will obtain this particular data element from data storage table 44-62. As a result, unproductive data requests over network bus 44-50 are also eliminated. Thus, in this embodiment the transfer of the data aging timer value among peer nodes connected on a network can produce significant reductions in data communications requirements. It should also be noted that another alternative to transferring the data aging timer from the network controller containing the requested data in its data storage table is to transfer the remaining time available on the data aging timer. This would allow the receiving network controller to avoid the requirement to calculate the remaining time during which the received data would be valid. It should also be noted that the use of the aging timer in a distributed facilities management system (FMS) further allows the user to define variable valid time periods for individual pieces of data. For example, a slave controller accessing data from a sensor sensing outside air temperature need not access the data as frequently as a sensor monitoring the temperature of a furnace. This is because the rate of change of outside air temperature is slower than the rate of change expected in a furnace. Thus, the data aging timer would be different depending on the variability characteristic of the data. In lieu of user defined data aging timers, the default values which are automatically implemented in the absence of further user defined information can also be programmed. In distributed facilities management systems, reliability of the data received (or not received) is often an issue. According to the present invention, as an aid to consistency and completeness, each data value passed between features of the facilities management system is tagged with a reliable/unreliable indicator. As shown in Figure 45, when data is requested in function block 45-1, the received data is tested at decision block 45-3 to determine if the received data was within the expected range. If not, one possible alternative in decision block 45-5 is to execute processing that determines if an alternate source of the data is available. Such processing may include sorting through directories to identify other physical locations in the network where the data is located. For example, the source data may be stored at another memory location in the same or another node, or the same data may be available from another sensor. Such processing could also include determining if a substitute for the unreliable data could be derived from other data available on the network. Function block 45-7 tests to determine if the alternate sources have been exhausted. If not the data could be obtained from an alternate source and retested in decision block 45-3. If no alternate source is available or if the alternate sources are exhausted, another option is to use the previous -12— value of the data. Thus, function block 45-9 tests if the previous value is available. If a previous value is available, it would then be determined if the previous value is useful in this process at 45-11. If so, the previous value is used as shown in function block 45-13 and the data is tagged with a reliability indicator appropriate to such old data in function block 45-15. If a previous value is not available or not useful, in function block 45-17 a decision is made as whether alternate control is available. If not, or if alternate control is determined not to be useful, as shown in function block 45-19, the data can be used and tagged with an indication of its unreliability. Of course, if alternate control is available, such alternate control techniques can be executed as shown in function block 45-21. New data received in the alternate control process would also undergo reliability testing as shown in function block 45-23. In any case, once data is tagged with a reliability indicator in function block 45-15, the data can then be passed on to other features as shown in function blocks 45-25 and 45-27. This provides an indication of the reliability of the data which can be included in intermediate calculations as an indication of the reliability of an ultimate calculation. The use of the reliability indicator is discussed further below relative to control of proportion and integral and derivative (PID) control loops. SUBSTITUTE SHEET -127a- According to another aspect of the invention, Figures 46A and 46B show a proportional plus integral plus derivative (PID) loop object. The PID loop object SUBSTITUTESHEET 2 is implemented in software at the software object level, as discussed previously. Thus, the PID loop object has a data base manager which manages processes and attributes stored in a storage means of a node or network controller, as do other software objects. Within the facilities management system, according to the invention, tasks for processing PID loops are divided among a PID data base manager task and 16 PID loop execution tasks. Thus, a PID controller may control up to 16 instances of the PID loop. Figure 47 shows a control loop with PID processing. The PID data base manager first provides an interface to other tasks in the network which may read data, e.g. 47-5, from a PID loop, write to a PID loop, or command a PID loop. The second PID data base manager task is to schedule processing of each of the 16 instances of PID loops. The third responsibility of the PID data base manager is to execute an auxiliary signal switch processing, output filter processing, high/low signal select processing and reliability switch processing in accordance with the inputs to these processing functions. As shown in Figure 46, a PID loop object has six inputs 46-1 which are used by an input conditioning process 46-3 to calculate a feedback value for the PID loop. Each of six inputs 46-1 may be floating point values such as analog parameters or references to attributes of other objects, as previously discussed relative to pseudo points. The references to attributes of other objects must be objects in the same physical digital control module (DCM) functioning as a PID controller. As an analog value, the input value or the value on other parts that accommodate analog values may change as a result of a command from a network controller. As previously discussed, if a port refers to an attribute of another object, the value of the attribute is obtained each time the corresponding processing is executed. This is achieved by sending a read attribute message to the specified object transmitting the message between tasks within the digital control module functioning as the network controller rather than over the N2 bus. It is also possible for ports to be individually overridden in which case, the override value is used as the value of the port until a command to release the override is received. If a port is an analog value, the last value commanded by the network controller is remembered and acted upon when the command to release is received. Only the network controller initiates and releases overrides. The setpoint input 46-5 may also be a floating point value or a reference to an attribute of another object, as previously discussed. The setpoint value 46-5 is the desired value of the feedback value and it is used in PID processing 46-7. Offset value 46-9 may be a floating point value or a reference to an attribute of another object. The offset value 46-9 performs two functions. If input conditioning processing 46-3 determines that all 6 sealers 46-11 are 0, then PID processing 46-7 is disabled and offset value 46-9 is used as the output of PID processing 46-7. If any of the 6 sealers 46-11 is not 0, offset value 46-9 is added to the output value calculated by PID processing 46-7. The offset may be used to introduce other control actions to the PID processing where it may be used to indicate the first output command the PID processing issues on start-up. High saturation limit 46-13 may be a floating point value or a reference to an attribute of another object. High saturation limit 46-13 is an input directly to PID processing 46-7. PID processing is prevented from issuing a command to the PID output above this high saturation limit 46-13. Low saturation limit 46-15 may also be a floating point value or a reference to an attribute of another object. A saturation limit 46-15 is provided directly to PID processing 46-7 and establishes a lower limit below which PID processing 46-7 will not issue a command to the PID output. Auxiliary signal input 46-17 may be a floating point value or a reference to an attribute of another object. The auxiliary signal input 46-17 is an alternate input that may be passed on to the output of auxiliary signal input processing 46-19 discussed below. High/low signal input 46-21 may be a floating point value or a reference to an output of an another object in the digital control module functioning as a PID controller and is an alternate input that may be selected for passing on by high/low select signal processing 46-23. The 8 outputs 46-25 are used to adjust manipulated variables, e.g., of a controlled process to desired states so that the setpoint and feedback variables are equal. The outputs refer to any attribute of any object in the same physical PID controller. The command from the PID loop is routed to each of the objects defined in these references. The PID processing also uses this information to determine if the object specified by this reference has been overridden by some other task. Certain parameters are analog values and cannot be overridden. The six sealers 46-11 are each floating point values to represent coefficients for each of the corresponding six inputs 46-1 to input conditioning processing 46-3. Sample period 46-27 has a range of 1-32767 seconds and determines how often the PID processing 46-7 is executed for a PID loop. Proportional band 46-29 is a floating point value which sets the sensitivity of the PID processing 46-7 to the difference between the feedback value and the setpoint value (the error) . The magnitude of the error causes a swing in output value. A positive value indicates a reverse acting control while a negative value indicates direct acting control. Of course, these controls could be reversed without violating the spirit of the invention. Integral time 46-31 is a floating point value which provides the PID processing sensitivity to the integral of the error. This is the time it takes the integral term to equal the proportional term given a constant error. Setting this value to 0.0 removes the integral action from the PID control processing. Derivative weight 46-33 also is a floating point value and gives the PID processing sensitivity to the rate of change of the feedback value. This term in conjunction with the integral time and the proportional band determine the amount of the derivative control provided. Setting this value to 0.0 removes derivative action from the PID control processing. Dead band parameter 46-35 is a floating point value which is compared to the absolute value of the difference between the set point and the input conditioned feedback. If this dead band value is not exceeded, no error change is considered by the PID processing 46-7. Hysteresis compensation bias 46-37 ranges from 0.0 to 100.0 and represents the amount of hysteresis encountered between the output point and the feedback point. This proportional value is used to compensate for process hysteresis. Feedback value 46-39 is calculated by input conditioning processing 46-3 and is a floating point value. PID processing 46-7 attempts to make feedback value 46-39 equal the set point value 46-5. The start data 46-41 includes information from previously iterations of the PID processing 46-7. In the first pass to PID processing 46-7, these values are set to 0.0, except for the previous direction value which is initialized to 1.0. The historical data includes the previous feedback value applied for derivative control, the previous integral term supplied for integral action and bumpless transfer, the previous hysteresis compensation bias for hysteresis removal, the previous output value for hysteresis removal, and the previous direction of output values for hysteresis removal. The previous direction of -133- output values is set equal to one for increasing values and equal to minus one for decreasing values. The processing of PID loops is divided among a data base manager task and 16 PID loop execution tasks. As such, the PID controller digital control module may control up to 16 instances of PID loops. The PID data base manager task has 3 primary responsibilities. First, to provide an interface to other tasks or objects in the PID controller or node which may want to read data from PID loop, write data to a PID loop, or command a PID loop. The second task of the PID data base manager is to schedule processing upon each of the 16 instances of the PID loop. The third responsibility is execution of subsidiary processing which may include auxiliary signal switch processing 46-19, output filter processing 46-43 in accordance with filter weight 46-61, high/low signal select processing 46-23 to generate H/L selected flag 46-75, and reliability switch processing 46-67 producing reliability value 46-73. In order to perform these tasks, the PID data base manager can react to two types of write record messages. The first is the ADD LOOP message which adds a PID loop to the data base. It also causes the configuration information for that loop to be written to an EEPROM so that the loop will be automatically added once power is returned after a power failure. The second type of write record message is the DELETE LOOP message. This causes execution of the PID loop to cease and the definition of the loop to be disabled. It also causes the object connected to the output of the SUBSTITUTE SHEET -1 33a- loop to b e notified that the loop is no longer defined. SUBSTITUTE SHEET The PID data base manager also accommodates two types of read record messages. The READ CONFIGURATION read record message causes the current working definition for the given PID loop to be formatted and sent back through the N2 bus to the network controller. The other read record message is READ CURRENT STATE. This causes information on the current state of the PID loop along with values used during the last iteration of the processing to be sent via the N2 communication bus to the network controller. START UP causes a PID processing 46-7 to react as if it had just been added. All historical data for the processing is reinitialized. The first output from the PID processing will then be based on the current offset 46-9 and the correction due to the current proportional control. A write attribute causes the specified attribute of the given PID loop to be set to the value in the message. This causes the output of the PID loop to change as a result. A read attribute causes the current value of the attribute to be returned to the requestor. If the attribute is override, the override value is returned. If the attribute is a reference to an attribute of another object, the read attribute message is redirected to the destination object. Where valid, an override attribute causes the value in the message to take precedence over the normal value the input would receive until a release attribute message is received for that attribute. A release override attribute causes the effect of the override attribute message to be removed. The PID data base manager also causes reporting of change of states. Such change of state reported include changing of a PID loop reliability flag 46-45, changing of a high saturation flag 46- 47, changing of a low saturation flag 46-49, and changing of a PID processing reliability flag 46-51. These flags are discussed below. The primary function of the PID loop data base manager is to provide scheduling. The PID loop data base manager continuously monitors the amount of time that has elapsed since the last time the PID loop was processed. When the sample period amount of time 46-27 has elapsed, the PID data base manager task collects the current state of the ports used by the PID processing 46-7. To collect the current state of the ports used by PID processing 46-7, the PID data base manager determines if the port is in an override condition or is defined as an analog value or an reference. As previously discussed, if an override, the override value is used as the value of the port. If the port is an analog value its value is used, and if the port is a reference, a read attribute message is sent to the object specified and the value returned is used as the value of the port. The PID data base manager checks the reliability of the data and the response and flags the port as reliable if the data received is determined to set that category. It should be noted that the PID data base manager executes a priority scheme to allow each PID loop to be processed every sample period within 15% of its sample period. This is done through a series of PID executive tasks which are each given a different priority. When the definition for a PID loop is added to a PID controller, the PID data base manager determines which PID executive task will provide the execution for that PID loop based on the sample period of the PID loop. PID loops with shorter sample periods are assigned higher priority PID executive tasks. PID loops with longer sample periods are assigned to tasks with lower priorities. When a PID loop is deleted from the PID controller, the PID data base manager task rearranges the association between PID loops and PID executive tasks according to the sample periods. When the sample period of a loop is changed, the priority of the loops is rearranged. After collecting the current state the PID executive task also provides any historical data needed. The PID data base manager then begins executing input conditioning processing 46-3. Input conditioning processing 46-3 provides for input summation, difference, averaging and various other accumulative functions or for the instantaneous maximum or minimum of the given inputs. The accumulative function, chosen by setting the input function attribute 46-100 to 1, is as follows: 6 Feedback value =( Σ scalar (n)* input value (n) ) n=l It should be noted that if the input is a reference to a object of another attribute and is null, then no point has been specified and a sealer of zero is used. If the scalar is zero then the input is ignored. The minimum function, chosen by, setting the input function attribute to 2 is as follows: minimum of scalar (1) * input value (1) or, scalar (2) * input value (2) or, scalar (3) * input value (3) or, scalar (4) * input value (4) or, scalar (5) * input value (5) or, scalar (6) * input value (6) The maximum function, chosen by setting the input function attribute to 3 is as follows: maximum of scalar (1) * input value (1) or, scalar (2) * input value (2) or, scalar (3) * input value (3) or, scalar (4) * input value (4) or, scalar (5) * input value (5) or, scalar (6) * input value (6) The 16 PID execution tasks are identical and differ only in their priorities as discussed above. Upon each iteration of the PID processing 46-7, the PID data base manager sends one of the PID executive tasks all the needed data to perform the processing for one of the instances of the PID loop. Upon completion of the PID processing, the PID executive task sends the calculated output 46-53 along with all the updated intermediate results to the PID data base manager task. It should be noted that no data about a PID loop is stored between iterations. PID processing in general is as follows: E(t) = (setpoint (t) - feedback (t) ) Pterm (t) = 100 * E (t) / Pband Iterm (t) = ( (T / Itime) * Pterm (t) ) + (r τ /Itime) + Iterm (t-1) Dterm (t) = Dweight * (Itime / 4T) * (100 / Pband) * feedback (t-1) - (feedback (t) ) OUT (t) = Pterm (t) + Iterm (t-1) + Dterm (t) + Offset (t) + Hysteresis compensation (t) Where: F (t) = The value at time t F (t-1) = The value at the previous iteration E (t) = The error at time t Pterm (t) = The proportional control contribution at time t Iterm (t) = The integral control contribution at time t T = The sample period Dterm (t) — The derivative control contribution at time t Setpoint (t) = The set point at time t Feedback (t) = The feedback value at time t Pband = the proportional term coefficient Itime = The integral time coefficient Dweight = The derivative term coefficients Offset (t) = An externally controlled compensation term Hysteresis compensation (t) = The action needed to compensate for hysteresis in the system Whenever the output command from PID processing 46-7 changes direction of travel (that is the derivative of PID processing output 46-53 changes sign) PID processing 46-7 may be configured to compensate for any hysteresis that occurs in the process between the output of the PID controller and the associated input. This is done by adding (or subtracting) the hysteresis compensation value 46-35 to the output 46-53 of PID processing as the direction of travel is increasing (or decreasing) . Bumpless transfer describes the reaction of PID processing 46-7 as control is transferred from one control method such as human control or another PID loop, to PID processing 46-7 of this loop. The control reaction is predictable, and is based on a difference between the feedback and set point as well as the previous command sent to the output just before control was transferred to PID processing 46-7. Whenever the auxiliary signal switch enable attribute is set, or all the outputs that might receive the command from PID processing are overridden, PID processing 46-7 goes into a tracking mode. In the tracking mode, PID processing 46-7 prepares for bumpless transfer by continuing to calculate Pterm(t) . When one of the outputs is released from the override condition, or the auxiliary signal switch enable attribute is reset, the PID executive task obtains the value the output was commanded to and uses it along with Pterm(t) from the previous iteration to perform the bumpless transfer. In the case of an override due to Hand/Off/Auto switch being in the Hand or Off position, this last commanded value is not available. Therefore, bumpless transfer is not provided once the switch is returned to the Auto position. The High and Low Saturation Limit inputs 46-12 and 46-15, typically specified in percent full scale deflection of the output, specify the boundaries which the command to the output of PID processing must stay within. PID processing 46-7 provides the facility of determining and annunciating when PID processing has become saturated, that is PID processing can not command the output to reach set point. PID processing is determined to be saturated when the command for the output for 40 consecutive iterations has been within 1% of the High Saturation Limit value 46-13, or the output for 40 consecutive iterations has been within 1% of the Low Saturation Limit value 46-15. Once PID processing has been determined to be saturated, either the High Saturation Flag 46-47 or the Low Saturation Flag 46-49 is set accordingly to annunciate the fact. This in turn causes the PID data base task to issue a change of state message so that functions in the network controller (NC) may act accordingly. These flags are reset once the Auxiliary Signal Enable flag 46-55 is set, or all the outputs are placed in an override condition. Saturation recovery is also provided by PID processing 46-7. The processing is designed so that the integral action does not "windup" once the processing attempts to command the output beyond the values specified for the High and Low Saturation Limits. After executing PID processing 46-7, the PID executive task sends a message back to the PID data base manager task containing the new value for the PID Output Value attribute 46-53, along with all the updated intermediate results needed for the next iteration of PID processing for this PID. The PIDEXEC task may then call other specialized processing. This call may suspend the other ongoing processing or it may provide data on the current iterations of the PID processing. A call to suspend specialized processing is sent when a process loop is determined to be unstable, or when it has been determined PID processing 46-7 does not have control of the outputs of the PID loop as discussed below relative to fault tolerant processing. This condition is indicated when the PID loop is determined to be unreliable, the PID processing is in the tracking mode, or the Auxiliary signal switch processing 46-19 is commanded by the Auxiliary signal switch enable attribute 46-55 to pass the Auxiliary signal input 46-17 to output 46-57, or High/Low Signal Select processing 46-23 has selected the High/Low Signal input 46-21. If none of the aforementioned conditions exist, then the appropriate data on the current iteration of the PID algorithm is sent in calls for further processing. It is also possible to by-pass PID processing to insert a signal in place of the signal 46-53 which normally comes from the output of PID processing 46-7. If all 6 sealers 46-11 are 0, PID processing 46-7 is by-passed and the value of offset 46-9 is used as the PID output value attribute 46-53. PID loop object 46-2 further provides that the output of PID loops can be effected according to the status of auxiliary signal switch processing 46-19, output filter processing 46-43 and high/low signal select processing 46-23. This occurs when the PID data base manager task receives a write attribute message that changes the input of one of these algorithms or the PID executive task for the PID loop has finished execution and has sent a message to the PID data base manager checking in the changes it has made to the configuration of the PID loop. The auxiliary signal switch processing 46-19 examines the state of auxiliary signal enable flag 46-55. If the flag is set, the value of the auxiliary signal input 46-17 is passed to auxiliary switch value attribute 46-57. If auxiliary signal input 46-17 is unreliable, the last reliable auxiliary switch value 46-17 is passed on. If the auxiliary switch enable flag 46-55 is reset, the value of the PID output value attribute 46-53 is passed to the auxiliary switch value attribute 46-57. Output filter processing 46-43 receives its value from auxiliary switch value attribute 46-57 and performs a first order filtering upon the value. The output is placed in the output filter value attribute 46-59. Filter weight attribute 46-61 is used to define the effectiveness of the filter and can a range of 1.0 to +10 23 , wherein a filter weight of 1.0 effectively disables the filtering. Filtering is performed according to the following equation: Output filter value = previous filter values + ((1/filter weight)*PID output value - previous filter value) ) . The previous filter value is the value calculated in the last iteration. The above equation is calculated every sample period or every time the auxiliary signal input 46-17 is changed or every time the offset 46-9 is changed when all the sealers are 0. If a previous filter value does not exist because the previous iteration's data was unreliable, or because it is the first pass through the processing for this instance, the auxiliary switch value 46-57 is passed directly to the output filter value attribute 46-59. The last reliable output filter value attribute 46-59 is issued to the output filter value if there is a math error while calculating the filter output. High/low select processing 46-23 compares the output filter value attribute 46-59 with the value of the high/low signal input 46-21. If the high/low select state attribute 46-63 is set, the greater of the two inputs is passed to the high/low select value attribute 46-65. If the high/low select state attribute 46-63 is reset, the lesser of the two inputs 46-21 and 46-59 is passed on. In the event that the high/low signal input 46-21 is unreliable, the PID loop unreliable flag will be set in the high/low select value attribute will remain at its last reliable value. The high/low select flag attribute is set when the high/low signal input 46-21 is selected. A change in the state of this flag causes a report to be sent over the N2 bus. Reliability switch processing 46-67 reflects the reliability of the commands issued to the outputs 46-25 of the PID loop. During processing for the PID loop, should the input data for any of the PID loops become unreliable, the output of the processing remains at the last reliable output value for the loop. In addition, the PID loop reliability flag 46-45 is set to be unreliable whenever the data supplied by the high/low signal attributes 46-65 is unreliable. This flag is also set to an unreliable state when any of the following conditions occur: 1. If the condition of the auxiliary signal enable flag 46-55 is set to route the auxiliary signal input 46-17 to the outputs of the PID loop, and the auxiliary signal input 46-17 is unreliable. 2. If the PID output attribute 46-53 is routed through the auxiliary signal switch processing 46-19 and the calculations used to generate the PID output attribute 46-53 are determined unreliable. These calculations are deemed unreliable when any of the ports used by the PID processing 46-7 receives unreliable data or when a math error, such as a division by 0, has occurred during the calculation. Following the execution of the high/low signal select processing 46-23, the PID data base checks the PID loop reliability flag 46-45. If this flag is reliable, the PID data base issues the output command to the output specified for the given PID loop definition. If the PID loop is unreliable, and the unreliable response selector flag 46-69 is reset, the PID data base manager issues the last reliable output command from the high/low signal select processing 46-23 to the output. Otherwise, it issues the command specified by reliability default attribute 46-71 to the output. The PID data base manager task sends the write attribute command to the appropriate object data base manager specified by the output value attribute 46-73. The following values are supplied by the PID processing 46-7 on completion of execution. The PID data base manager task ensures that the current PID loop data base reflects these changes. The PID output value is the command to be issued to the output point which drives the controlled variable toward the set point value. It may be thought of as percent of full scale between 0.0 and 100% deflection. The PID processing reliability flag 46-51 is either a 0 or 1 and indicates whether an error in the calculation has occurred or one of the ports used by the PID processing 46-7 is unreliable. The PID loop reliability flag 46-45 is either a 0 or 1 and if 0 indicates that the command being sent to the outputs of the PID loop is based on reliable data. Additional loop parameters are returned for the next execution of the PID processing 46-7. These parameters include the feedback value for derivative control, the integral term for integral action and bumpless transfer, the hysteresis compensation bias for hysteresis removal, the output value for hysteresis removal and the direction of the output values (increasing = 1, decreasing = minus 1 for hysteresis removal, the previous feedback value and the error calculated between the set point and the feedback value) . -1 6- The language also has a PI_RESET function which is designed to reset a setpoint by means of a programmed proportional-integral calculation. It is designed for use in closed loop systems. The control system 47-1 shown generally in Figure 47 has an input device 47-3 which receives inputs along line 47-5 and generates control variables along line 47-7, often known as a feedback variable. A control variable on line 47-7 provides an input to a proportional-integral-derivative (PID) device for object 47-9 and to an object 47-11 which provides a fault tolerant control strategy. In the present context, typical objects include hardware and software combinations which perform functions desirable for a control loop. Such objects are typically implemented in software and stored in a memory portion of one or more automated processing control nodes 47-2 operating as a network. The organization of a system having hardware and software objects according to the present invention has previously been discussed. The PID loop 47-4 is typically structured to operate under normal circumstances without assistance from the fault tolerant control strategy object 47-11 in control node 47-2. PID object 47-9 generates and receives PID loop variables 47-13 and also provides inputs and receives outputs from fault tolerant control strategy object 47-11. The PID output on line 47-15 is routed both to the fault tolerant control strategy object 47-11 and to switch 47-17. The Output Device Command on line 47-19 of switch 47-17 can thus be switched between the PID output and the output of the fault tolerant control SUBSTITUTESHEET -14όa- strategy object SUBSTITUTE SHEET 47-21 based on command on line 47-23 also generated by the fault tolerant output control strategy. The fault tolerant strategy of object 47-11 also receives process constants on line 47-25 and another output on line 47-27 generated by input device 47-29 which receives input signal 47-31. The output device driving command on line 47-19 from switch 47-17 constitutes a manipulated variable driving output device 47-33 which generates a related manipulated variable on line 47-35. The related manipulated variable on line 47-35 is input to process 47-37 which completes the control loop by generating signals on lines 47-5 and 47-31 to input devices 47-3 and 47-29. The purpose of the control loop is to generate manipulated variables on lines 47-19 and 47-35 to control the output device and to accomplish the desired process 47-37. In normal operation, PID control is accomplished and switch 47-17 is set via signal 47-23 to PID output line 47-15. Thus, the fault tolerant control strategy object 47-11 merely monitors the status of control variable on line 47-9 and does not participate in the actual control of the loop. Fault tolerant control strategy object 47-11 monitors control variable on line 47-7 to verify that the control variable is within a reliable range of values. When fault tolerant strategy object 47-11 determines that control variable on line 47-7, the feedback variable, is no longer within the reliable range, the fault tolerant control strategy object 47-11 directs switch 47-17 to route to the output device command signal on line 47-19, the fault tolerant control strategy object output 47-21. This is done via switch command line 47-23. At this point, based on process constants on lines 47-25 and signals 47-27, the fault tolerant control strategy object 47-11 implements a strategy which allows the related manipulated variable on line 47-35 to continue to be adjusted even though the feedback, the control variable on line 47-7, is no longer reliable. Thus, the loss of feedback in the PID control loop does not result in the loss of control over output device 47-33 or related manipulated variable on line 47-35. Through input device 47-29 which monitors signals on line 47-31 from process 47-37, the fault tolerant strategy object 47-11 responds to dynamic changes in process 47-37 along with process constant 47-25 to generate signals to control the manipulated variables on lines 47-19 and 47-35. Thus, even under a failed condition, it is possible to retain a level of control over process 47-37 which minimizes the effect of the failure. In one example, the fault tolerant control strategy addresses the typical HVAC processes including heating, cooling, and mixed air discharge temperature control. Figure 48 shows phases of implementing a fault tolerant control strategy. These include commissioning 48-1, initialization 48-3, process monitoring 48-5 and control 48-7. Figure 49 outlines inputs and outputs of the process which takes place in implementing a fault tolerant control strategy. During initial commissioning 49-301 the fault tolerant control strategy object is informed where parameters are stored in a memory accessible to the fault tolerant control strategy object 47-11, and what parameters are important to the process being controlled. For example, air temperature and flow rate parameters may be used to determine if, for example, a chilled water valve should be open or closed. Thus, initial commissioning identifies the variables which are used in the fault tolerant control strategy. In a fault tolerant controller used in an HVAC system, there are three classes of information or parameters. The first is a static set of variables 49-303 which is the same for each PID loop. These include the setpoint, a proportional band, and the control variable. A second set of parameters are process variables 49-305 which are the actual analog inputs obtained. These differ depending on the HVAC process 49-307. For example, some HVAC processes require outdoor air temperature while others require water temperature or pressure. Finally, there are process constants 49-309 which are PID loop dependent as a result of their dependency on physical devices used to monitor system performance. In implementing a fault tolerant control strategy object, it is also necessary to provide information concerning the configuration of the PID loop. This can be done either by programming the fault tolerant control strategy in a programming language or as a user block of a graphical programming tool 47-311. In either case, the routine is added to a control system database which can be accessed by the fault tolerant control strategy object and executed in a control node. During initialization phase 49-313, a routine in the fault tolerant control strategy object 49-11 collects data concerning the process constants and the static PID loop and performs a stabilization check 49-315. As previously indicated, the constants can be hard coded and need only be read into the fault tolerant control strategy object once. The three classes of PID loop parameters represent the most recent state of the controlled process. The commissioning phase previously discussed provides the information on where these parameters are located in memory. During initialization, the parameters are read by the fault tolerant control strategy software object. Initialization then verifies that a set of reliable static parameters 49-317 required for process control can be obtained. This is because a full set of reliable PID static data is necessary to allow execution of a fault tolerant control strategy. Initialization, phase 49-313 verifies stabilization of the PID loop control, rather than the variables or parameters. A PID loop is stable if the controlled variable remains close to the set point and fluctuations in the manipulated variable are small. As part of the initialization phase 49-313, predetermined numerical measures of oscillation and sluggishness 49-319 are evaluated against the performance of the control loop. During the monitor phase 49-321, the fault tolerant control strategy object 47-11 presumes stable process control and updates the static PID -151- variables and the process variables. The primary function performed during the monitor phase is evaluation of the reliability of the control variable 47-7 or feedback of the PID loop. This may be based on several physical analog inputs in the PID loop itself if, for example, the feedback is multidimensional. If this feedback, the control variable on line 47-7, goes unreliable, then the control mode of operation is entered. It should be also noted that it is not absolutely necessary to monitor the actual feedback or control variable. Control variable 47-7 may be the output of a software object generating the control variable. In this case, the control variable is defined to be unreliable when any of the inputs to the software object generating the control variable become unreliable. Thus, if an analog input to the software object generating the control variable is detected to have become open or shorted, or if a non-legitimate value is generated during data manipulation in the software object (e.g., dividing by zero) , then the fault tolerant control strategy assumes that the control variable 47-7 or the feedback has become unreliable. When the control function 49-323 is entered, the fault tolerant control strategy object 47-11 calculates the value to be used in place of the value generated by the PID algorithm. As indicated previously, this is basically an open loop control based on a model of the system and the current state of the variables. There need be no requirement of linearity between the process variables and the calculated output command. Since the system SUBSTITUTE SHEET responds to the current state of the process 47-37, it is also possible to respond to changes in the setpoint, as shown in the equation given below. It should be noted that the fault tolerant control strategy object 47-11 may attempt to execute control at the same rate as the PID controller. However, in most cases, control will be slower due to limitations of network performance. As previously indicated, fault tolerant control strategy object 47-11 control is ordinarily implemented in a control node and not in the PID device which is part of the loop. Thus, multiple communications over a local bus between the PID loop and the control node, and perhaps over a network bus interconnecting multiple control nodes increase loop response time under fault tolerant control strategies. As previously discussed, a fault tolerant control strategy can be based in part on a model of the control process. The fault tolerant controller block executes once every twenty sampling periods of the PID controller. The process monitor and output switch functions execute once each sampling interval of the PID controller. In one system configuration shown in Figure 50, the functions of the process monitor and output switch can be implemented directly in a Digital Control Module while the fault tolerant controller functions are implemented in the Network Controller. Various variables required to implement a fault tolerant control strategy are listed in Table 1. TABLE 1 Inputs Setpoint Variable (reference variable) ControlledVariable (feedbackvariable) Primary Manipulated Variable (control output variable) Secondary Manipulated Variable (Interacting control output variable) Primary Process Variable (feedforward variable #1) SecondaryProcess Variable (feedforward variable #2) Controller Proportional Band Controller Sampling Period Controller High Saturation Limit Controller Low Saturation Limit Controller Error Tolerance Fault-Tolerant Enable Flag P: Fault-Tolerant Output Local Variables Reference Controlled Variable Reference Primary Manipulated Variable Reference Secondary Manipulated Variable Reference Primary Process Variable Reference Secondary Process Variable Reference Controller Proportional Band Figure 52 is a more detailed illustration of the fault tolerant control of the invention. PID controller 52-1, process monitor 52-3 and fault tolerant controller 52-5 all receive the setpoint SP and control variable CV. PID controller 52-1, process monitor 52-3 and fault tolerant controller 52-5 all perform individual processing which is discussed in more detail below. Based on conditions in the system, fault tolerant controller 52-5 generates a flag output which is routed -154- to an output switch 52-7. In addition, fault controller 52-5 generates a backup output which is also routed to the output switch. The backup output is determined by the following equation: MVl=MVl o +EFF*(MV2-MV2 o )+(100%/PB o )*(SP-CV o +(EFF-l)*(PVl- PV1 0 )-EFF*(PV2-PV2 0 ) ) ; with EFF being limited to a range of 20%-80% The other input to the output switch is manipulated variable MVl produced in PID controller 52-1. Under normal circumstances, i.e. when the system is not experiencing a fault, fault tolerant controller 52-5 sets a flag to output switch 52-7, such that the output of switch 52-7 is a primary manipulated variable from the PID controller 52-1. Generally, the manipulated variable corresponds to one output of a PID process as shown in Figure 47. When a fault condition exists in the system, the flag causes the output switch 52-7 to route the backup signal from fault tolerant controller 52-5 to its output. As shown in Figure 47, the output of the switch can be used to drive an output device. Thus, a failure in the process control loop is accommodated by the fault tolerant controller, so that the output device remains operational, even if in a degraded state. Figures 53A and 53B illustrate processing that takes place in process monitor 52-3. Typically, the process monitor operates in a digital control module. A network controller typically executes the process 20 times slower than the monitor rate possible at the digital control module. Thus, processing is different in the process monitor depending on whether or not a SUBSTITUTESHEET execution has taken place in the network controller. Prior to initiating processing, it is first determined in test block 53-73 if the control variable is reliable, as discussed herein. If not, the variables shown in block 53-71 are set and control is returned to test block 53-73. In test block 53-1 the process monitor first determines if the interval is greater than or equal to 20 times the process rate in the digital control module. If this is not the case, the manipulated variable is tested as shown in blocks 53-3 and 53-5 to determine if it exceeds maximum and minimum outputs which have already been detected and stored by the monitor process. If the manipulated variable is beyond these stored values, then the appropriate maximum and minimum output is set equal to the manipulated variable in function blocks 53-7 and 53-9. In either case, in function block 53-11, an error value is determined to be the absolute value of the setpoint minus the control variable. As shown in function blocks 53-13 and 53-15, if the present error exceeds a maximum error previously monitored by the process, the maximum error is set equal to the present error. The above process continues to repeat until the interval is determined to exceed 20 times the processing time of the digital control module in function block 53-1. At this point, control transfers to other function blocks which determine whether or not the system is saturated and whether or not the output is stable. If the maximum output as previously determined during processing previously discussed exceeds one percent less than the output high defined for the process, a high saturation variable is incremented. If not, the variable is set equal to zero as shown in -155a- complete SUBSTITUTE SHEET function blocks 53-19 and 53-21. Similarly, if the minimum output as previously described is beyond the predefined limit of an output low variable, as shown in block 53-23, a low saturation flag is either incremented or set equal to zero, as shown in function blocks 53-25 and 53-29. At function block 53-31, it is determined if either of the saturation variables exceeds one. If so, a saturation flag is set "true" as shown in block 53-33 and if not, a saturation flag is set "false," as shown in function block 53-35. Processing in the process monitor then proceeds to identify the number of deviations beyond specific percentages of the range of high and low outputs. For example, function block 53-37 determines if the differences between the maximum output and minimum output of the process exceeds 15% of the high and low outputs allowed. If not, a deviation variable is set equal to zero in function block 53-41. However, if the difference does exceed 15% of the allowed difference between the high and low outputs, the deviation variable is incremented as shown in function block 53-39. Similarly, function blocks 53-43, 53-45, and 53-47 show a counting of the deviations from 9% while function blocks 53-49, 53-51, and 53-53 show how deviations beyond 5% are counted. It should be noted that since the deviation variables are reset to zero each time the difference between the maximum and minimum outputs is within the specified range, the deviation counts are incremented only in the case of consecutive variations beyond the specified range. Function block 53-55 is used to determine whether or not the process is stable. If there have been more than nine counts of deviations greater than 5% or five counts of deviations from 9% or three counts of deviations greater than 15%, function block 53-57 sets a STABLE variable to a "false" state. This indicates that the system is not stable. If these deviations are within the acceptable ranges, then function block 53-59 compares the maximum error with a band variable which defines an acceptable range of error. Again, if the maximum error is out of the range specified by the band variable, the process is considered to be unstable otherwise, the process is considered stable as shown in function block 53-61. Function block 53-63 resets the variables before returning control to the process monitor executive. It should be noted that the output minimum and maximum are typically set to 100% and 0% respectively. This assumes that the manipulated variable is provided in the form of a percent of full scale deflection. However, any other arrangement for adjusting a manipulated variable would be within the spirit of the invention. Figure 54 illustrates processing in a fault tolerant controller object. As shown in function block 54-1, if the interval previously discussed has not expired, function block 54-3 merely updates the interval and no further processing takes place. However, if the interval has expired, fault tolerant control processing occurs. First, the interval is reset to zero as shown in function block 54-5. Next, a reliability status of the control variable is tested in function block 54-7. When the status of the control variable is reliable, fault tolerant control processing then checks to determine if the output is saturated as shown in function block 54-9. If this is the case, the output is considered stable and no further fault tolerant processing occurs. If the output is not saturated, then the routine moves to function block 54-11 which checks the status of the STABLE variable previously calculated by the process monitor as discussed relative to Figure 53. If the STABLE variable is not "true", no further processing takes place. However, if the STABLE variable is "true", function block 54-13 determines if the data is reliable. If so, it sets the reference variables of the control variable, primary and secondary manipulated variables MVl and MV2, primary and secondary process variables PV1 and PV2, and the proportional band PB equal to the current corresponding values of the variables. Thus, the fault tolerant controller receives the most up to date values of these variables. The flag is set to FALSE as shown in function block 54-27 and control is transfered to function block 54-1 to test the interval. In function block 54-7, if the control variable status is determined to be unreliable, the fault tolerant control processing then examines the data. If the data is reliable, the setpoint, the primary and secondary process variables, and the secondary manipulated variable are set equal to the current values in function block 54-15. In function block 54-17, efficiency variable EFF is set equal to the reference primary manipulated variable stored in the object, limited in value to between 20 and 80% rather than over the full 0-100% range. Function block 54-21 then calculates the backup value which will be transmitted to output switch 52-7. The equation for calculating the backup variable is shown in function block 54-21. As the equation indicates, the backup variable is a combination of the primary manipulated variable stored in the object as modified by the secondary manipulated variables in percentages of the stored proportional band. Function block 54-23 shows that the backup is limited to fall between the low and high outputs specified in the object for the process being controlled. In function block 54-25 the flag is then set "true" to direct output switch 52-7 to route the backup signal to its output. Fault tolerant control processing then returns to function block 54-1. Figure 55 illustrates output switch processing. In Figure 55 if the flag is true, the output signal is set to be the backup on the switch, however, if the flag has not been set true by fault tolerant controller 52-5, and function block 55-5 determines that the status of the control variable is not reliable. The output at the switch is then routed to a previous or old value of the manipulated variable, as shown in function block 55-7. If the status of the manipulated variable is shown in function block 55-5 to be reliable, the old manipulated variable is replaced with a new manipulated variable and the output is set equal to the new manipulated variable in function blocks 55-9 and 11. Otherwise an old value of the manipulated variable is used. This terminates processing of the switch. As a result of the above described processing, it is possible for a process control loop to maintain operation in a degraded state even if the feedback variable has become unreliably an output is unstable or an error is outside of allowable limits. In order to reduce overall energy consumption, systems, such as facilities management systems, perform load rolling and demand limiting, which attempt to manage load induced energy consumption over time. The energy consumption is managed, for example, with a processor and a meter, and energy consuming load devices, or loads, are selectively deactivated, or shed. According to one aspect of the invention, load shedding can be a high level feature of a first node which operates to shed loads or elements of loads controlled by one or more other nodes of the system. It is also possible for a node to manage energy consumption from multiple sources. For example, in one embodiment a node supporting load shedding features monitors four energy meters. The nodes which support operation of the loads and load elements receive load shedding commands from the node supporting the load shedding feature. In response, the nodes receiving the commands deactivate the selected nodes. Dependance on communications between the node supporting the load shedding feature and the nodes supporting the loads is eliminated by incorporating a restore task into each of the load specific nodes. For example, in Figure 51, first node 51-1 contains a high level load rolling software feature 51-3 which is responsive to system energy consumption monitored by meter 51-5. Based on the level of energy consumption monitored, load rolling feature 51-3 determines the required reduction in energy consumption. This is compared against energy consumption values in load table 51-7 to identify one or more currently active loads which can be shed to achieve the desired energy reduction. Load rolling feature 51-3 then issues a command on high speed Nl bus 51-9 which is read by other nodes 51-11 and/or node 51-13. It should be noted that the communication protocol used between the nodes is not a factor according to this aspect of the invention. For example, the command from first node 51-1, could be directed to one or more specific nodes or could be broadcast to all nodes on the high speed bus 51-9. Nodes receiving load shed commands from load rolling features process the commands and deactivate the loads identified. For example, second node 51-11 would deactivate one or both of loads 51-15 and 51-17 while third node 51-13 would deactivate either or both of nodes 51-19 and 51-21. First node 51-1 could also issue commands to shed loads from more than one node, if that is required to achieve the desired energy consumption and does not violate any other rules programmed to prohibit deactivating specific combinations of loads. In addition to deactivating the loads, second and third nodes 51-11 and 51-13 perform local processing to restore the loads to operation at an appropriate time. Performing such processing locally relieves this responsibility from first node 51-11 containing the load rolling feature. This allows node 51-1 additional time for processing other tasks and improves system reliability by assuring the load is restored, even if the node which deactivated the load loses communication with the node containing the load rolling feature. Because load restore processing is localized in the node controlling the load, load restoration is independent of the feature and failure of the communications link 51-9 or first node 51-1 or downloading new information into first node 51-1 before the load is restored does not preclude the load from being restored to operation. Localized load restore processing is accomplished by defining objects with attributes that follow shed and restore characteristics rather than by incorporating these characteristics into the load shedding process, as in previous systems. Localized restore processing distributes processing of high level load shedding features. For example, attributes 51-23, 51-25 of software objects 51-27, 51-29 in nodes 51-11 and 51-13 describe the shedding and restoration characteristics of loads 51-15, 51-17 and 51-19, 51-21 respectively. Typically, such restoration and shedding characteristics include maximum off times, minimum on time after activation of the load and certain safety features. For example, a cooler turned off by a load shedding command may be reactivated if a monitored temperature exceeds a predetermined level. Thus, load shed processing is distributed on the network because the node initiating the load shedding is not required for restoring the shed load to operation, unless the node initiating the shedding also controls the particular load being shed. Since the loads again become operational, other features can also direct or monitor the same loads, even if the node initiating the load shedding goes off line at anytime. In a related aspect of the invention, demand limiting features programmed into nodes seek to maintain energy consumption levels below predetermined targets during known time intervals of peak demand. This reduces system operating costs by reducing energy consumption during such demand periods when a utility charges premium rates. During, for example, a 15 minute interval, demand limiting might evaluate energy consumption over the last 14 minutes and assume that for the next 1 minute in the future, consumption will remain constant. The feature then determines the total energy consumption for the 15 minute interval and then, using -163- load tables 51-7, identifies loads which can be shed t maintain the energy consumption level below predefined, stored target for the interval. Demand limiting, according to the invention, ca employ the same software object approach as describe previously for load rolling. This distributes deman limiting processing and allows restoration of the loa by a local restore process stored in the nod controlling the load. In the case of demand limiting, the load may be restored when an attribute of th software object indicates an operator initiated comman to restore the load. It should also be noted that th objects can accommodate immediate restoration o shedding loads if required in emergency situations, suc as fire. Figure 56 shows a network configuration with plurality of nodes 56-1, 56-3, and 56-5 communicatin with each other over a high speed bus 56-6. A previously discussed, each of the nodes may operat slave devices 56-9, 56-11, 56-13 over a local or slav bus 56-7. In order to reduce errors introduced by nois on the local bus 56-7, optical coupling can be used. Such optical coupling provides the nodes with signfican levels of isolation from signal noise introduced by th slave devices not optically coupled to the bus leads. External noise sources also produce RFI, EMI and othe error inducing effects. One such optical isolation approach is shown i Figure 57. The general configuration shown in Figure 57 is consistent with the RS/485 Electronic Industries Association specification. Additional noise isolatio is achieved by several techniques shown in Figure 57. S UBSTITUTESHEET One such technique is the use of pull up and pull down resistors to apply DC bias when devices are in a high impedance state. This DC bias is provided by resistor R381 which is connected to a positive 5 volt source, and R382 connected to the communications ground as shown in Figure 57. Thus, outputs J1A1 and J1A3 are biased to a DC level where the line drives and receives in device U49 are in the high impedance state. As a result, low level noise appearing on the signal lines does not generate a detectable input. Differential mode noise is noise showing up on the pair of transmit/receive wires as opposite polarity from one wire to the other. The bias voltage placed on the lines is a means of "swamping out" differential mode noise. It can do this because, without the bias, and with high impedance at all nodes, the lines are practically "floating." That is to say, noise is easily induced onto the line, both in common mode or differential mode. The bias placed on the line can easily "swamp out" the differential mode noise on these lines. Common mode noise is noise induced on both the lines of the local bus (the reference line is not included in this discussion, since data signals are never sent on that wire) in equal magnitudes with respect to earth ground. Since these noises are "looking" for a path to earth ground the lines from earth ground are isolated with the opto couplers. The circuits handle up to 2500 volts before an optocoupler would "break down" and let noise pass through. The opto isolators are protected with the tanszorbs and MOV circuitry. Therefore, common mode noises greater than [56V (MOV) + 6.5V (TRANSZORB) ] 62.5 volts would be shunted directly to earth ground via the MOV and transzorbs. The optical isolation portion of the node has several optical isolators. Optical isolator U50 has two parts. A first part of the optical isolator is responsive to transmit signal TXDN. This signal drives one portion of the pair of optical isolators in U50. The output of this first portion drives a line transmitter in U49, which as Figure 83 shows contains a line transmitter and a line receiver. In addition, retrigger ble one shot U51 responds to the transmit signal TXDN to source a current to an LED or other indicator which indicates that the node is transmitting data. In the transmit mode, a line transmitter portion of U49 provides signals to the plus and minus lines of the bus which drives the slave devices. The same plus and minus signal lines connected to the bus provide receive signals which can be received by the line receiver portion of U49, as shown in Figure 83. The output of the line receiver drives optical isolator U53. U53 then provides receive signals RXDN to the node. The received signals also drive another portion of retriggerable one shot U51. This provides an uninterrupted sourcing current to a light emitting diode or other indicator to show that the node is receiving data. It should be noted that the retriggerable one shots provide uninterrupted current to the transmit and receive indicators, so that the indicators remain constantly illuminated while data transitions are occurring in the transmission or reception of data. This is different from conventional approaches in which the LED or other indicator is flashed as signals are transmitted and received. This flashing introduces noise currents which do not occur in the present invention. It should be noted that the figure shows +5C and +5D power supplies. The +5C power supply is a communications power supply while the +5D power supply is a digital power supply. Separate power supplies are used to further reduce the effects of noise. A signal indicating a failure of one of the power supplies is produced by optical isolator U52. This optical isolator has a light emitting portion connected to the communications power supply and a light receiving portion connected to the digital power supply. If the +5C source goes bad, the POWER LED goes out because of a signal change at the "light receiving" part of the optocoupler. That signal is gated through logic to turn off the power LED. If the +5D goes bad, the power LED goes out because it is driven by the +5D power supply. The optocoupler isolates both supplies from each other. Thus, a failure of either power supply will produce an indication of a failure in the node. This is distinguished from conventional approaches in which a failure of the communications power supply would not be recognized in the receive mode and would only be recognized in the transmit mode from the absence of transmissions. In addition, by using the +5D supply on the light receiving portion of optical isolator U52, additional noise immunity is achieved. This is because the communication supply is further isolated from the failure indicating signal. The +5D supply may have high frequency noises present due to the use of crystals and fast logic switching of high-speed CMOS gates; the +5C supply may have noises on it which were brought in from the outside world on the local bus. These noises may be up to 2500 volts, peak, with no effect to the operation of the system. Finally, the present invention is distinguished from conventional systems by its use of a single pair of signal lines for both transmission and reception of data on the bus driving the slave devices. Finally, it should be noted that indicia defining the operating instructions for causing the system to function as described herein may be stored in EPROM or other suitable storage medium for use by the processors. The operating instructions may also be contained on other storage media such as a magnetic storage media having indicia defining the operating instructions for conveying the operating instructions into volatile memory should a volatile memory be desired for sequencing such a processor. The magnetic storage medium may therefore be retained for future use should the volatile memory suffer a power outage. Such storage media and processors are well known in the art and therefore have not been described in greater detail herein. While specific embodiments of the invention have been described and illustrated, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

Claims: What Is Claimed Is 1. A computerized control node for exchanging data with operational units, the node comprising: means for processing and storing data at multiple hierarchical levels; means in the storage means for storing features in a first software level, the features defining high level functions performed by the node, the first software level accessing software objects stored in a second software level under control of the processing means; means in the storage means for storing the software objects in the second software level, the second software level being arranged into one database for each of at least one predefined software object type, each of the databases having a corresponding software object manager; and means in the storage means for storing operational unit data in the third software level, the third software level being arranged into one database for operational unit data corresponding to each of at least one predefined operational unit type, each of the databases having a corresponding hardware object manager for conditioning the operational data unit into a form required by the software object managers. 2. The apparatus of claim 1, wherein each software object manager further comprises processing means in the processing means for: identifying data structures of the software objects in the corresponding software object data base; determining the software object requested by the feature in the first software level requesting data; and determining and extracting attributes of the software object needed to perform the high level functions of the features requesting data. 3. The apparatus of claim 1 wherein at least one software object manager further comprises means for accessing the processing means to report predefined conditions of software object attributes to features in the first software level. 4. The apparatus of claim 1 wherein the hardware object manager further comprises the processing means conditioning operational unit data differently for each operational unit type. 5. The apparatus of claim 1 further comprising at least one slave controller connected to at least one operational unit, the slave controller providing the operational unit data for storage in the third software level. 6. A computerized control node as recited in claim 1, wherein the computerized control node is an element of a facilities management system. 7. A method for exchanging data between computerized control nodes and operational units, the control nodes having processing and storage means, the method comprising the steps of: processing and storing data at multiple hierarchical levels; storing in the storage means features in a first software level, the features defining high level functions performed by the node, the first software level accessing software objects stored in a second software level under control of the processing means; storing in the storage means the software objects in the second software level, the second software level being arranged into one database for each of at least one predefined software object type, each of the databases having a corresponding software object manager; and storing in the storage means operational unit data in the third software level, the third software level being arranged into one database for operational unit data corresponding to each of at least one predefined operational unit type, each of the databases having a corresponding hardware object manager for conditioning the operational data unit into a form required by the software object managers. 8. The method recited in claim 7, wherein each software object manager further performs the steps of: identifying data structures of the software objects in the corresponding software object data base; determining the software object requested by the feature in the first software level requesting data; and determining and extracting attributes of the software object needed to perform the high level functions of the features requesting data. 9. The method recited in claim 7, wherein at least one software object manager further performs the step of: accessing the processing means to report predefined conditions of software object attributes to features in the first software level. 10. The method recited in claim 7 wherein the hardware object manager further performs the step of: conditioning operational unit data differently for each operational unit type. 11. The method recited in claim 7 wherein at least one operational unit is connected to a slave controller, the slave controller providing operational unit data to a control node and the control node storing the data in the third software level. 12. The method recited in claim 7, wherein the computerized control nodes and operational units are configured into a facilities management system. 13. The method recited in claim 7 comprising the further step of adding additional software and hardware objects of predefined object types to a node by downloading the node with additional instances of the object types. 14. The method recited in claim 7 comprising the further step of adding an operational unit of a new type other than one of the predefined types by incorporating into the node a hardware object manager for the new type of operational unit, the hardware object manager mapping information produced by the new type operational unit into an instance of an existing software object. 15. A storage medium including stored indicia of a plurality of operating instructions exchanging data between computerized control nodes and operational units, the instructions including instructions for: processing and storing data at multiple hierarchical levels; storing features in a first software level, the features defining high level functions performed by the node, the first software level accessing software objects stored in a second software level; storing the software objects in the second software level, the second software level being arranged into one database for each of at least one predefined software object type, each of the databases having a corresponding software object manager; and storing operational unit data in the third software level, the third software level being arranged into one database for operational unit data corresponding to each of at least one predefined operational unit type, each of the databases having a corresponding hardware object manager for conditioning the operational data unit into a form required by the software object managers. 16. Stored indicia as recited in claim 15 further comprising stored indicia of software object manager operating instructions, the software object manager instructions further including instructions for: identifying data structures of the software objects in the corresponding software object data base; determining the software object requested by the feature in the first software level requesting data; and determining and extracting attributes of the software object needed to perform the high level functions of the features requesting data. 17. Stored indicia as recited in claim 15 further comprising stored indicia of at least one software object manager having instructions for accessing the processing means to report predefined conditions of software object attributes to features in the first software level. 18. Stored indicia as recited in claim 15, wherein the hardware object manager comprises stored indicia of operating instructions for conditions of software object attributes to features in the first software level. 19. A facilities management system comprising: at least one computerized control node having means for communicating with other computerized control nodes and means for communicating with operational units, the operational units having means for monitoring and controlling a process; the computerized control nodes further comprising: means for processing and storing data at multiple hierarchical levels; means for storing features in a first software level, the features defining high level functions performed by the node, the first software level accessing software objects stored in a second software level; means for storing the software objects in the second software level, the second software level being arranged into one data base for each of at least one predefined software object type, each of the data bases having a corresponding software object manager; and means for storing operational unit data in the third software level, the third software level being arranged into one data base for operational unit data from each of at least one predefined operational unit type, each of the data bases having a corresponding hardware object manager for conditioning the operational data unit into a form required by the software object managers. 20. The facilities management system recited in claim 19, wherein each software object manager further comprises processing means for: identifying data structures of the software objects in the corresponding software object data base; determining the software object requested by the feature in the first software level requesting data; and determining and extracting attributes of the software object needed to perform the high level functions of the features requesting data. 21. The facilities management system recited in claim 19 further comprising means for at least monitoring at least one control process. 22. A method of locating data in a distributed network system having nodes with processing means and information storage means, comprising the steps of: downloading from a processor data elements and corresponding unique data element names to addressable data element locations in at least one of the nodes; referencing at least one data element by name from referencing nodes; in each referencing node storing binding information relating names and corresponding data element locations by searching the network for the location of a data element the first time the data element is referenced by the referencing node and storing by name in the referencing node the location of the referenced data element; for subsequent references by the referencing node to stored data element names, identifying the location of the data element from the binding information and retrieving the data element from the location defined in the binding information. 23. The method recited in claim 22 wherein the step of retrieving a data element further comprises: comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, again searching the network for a new location of the data element corresponding to the name referenced by the referencing node; if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with the new binding information including the new location of the data element and producing an error message if the name referenced by the referencing node is not found. 24. The method recited in claim 2,2 wherein the step of storing the binding information further comprises building a single binding information table in each referencing node. 25. The method of claim 24, wherein the step of building the binding information table further comprises: storing a table of data element names referenced by applications and software features in the node; and storing the binding information in the table the first time the applications and features reference the data element name. 26. The method recited in claim 24 further comprising the steps of: storing in each referencing node an index of references to unique data element names from applications and features in the referencing node and a corresponding location in the binding information table; and accessing the binding information of the data element names referenced by the applications and features by accessing the location in the binding table identified by the index for the referenced data element names. 27. The method recited in claim 22 further comprising; comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, searching the node identified in the binding information for another location within the identified node of the data element name; if the data element name is not found at said another location in the node identified in the binding information, searching remaining nodes on the network for a new location of the data element corresponding to the name referenced by the referencing node; if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with new binding information including an updated location of the data element and producing an error message if the name referenced by the referencing node is not found. 28. The method recited in claim 22 further comprising downloading binding information to nodes hosting the data elements. 29. A method of locating data in a distributed network system having nodes with processing means and information storage means comprising the steps of: downloading from a processor data elements and corresponding unique multi-part data element names having at least a first part and a second part to addressable locations in at least one of the nodes; broadcasting to all the nodes in the network a common first directory containing data element name first parts, the directory identifying the nodes on which names having the first parts have been downloaded; storing in each node at least a second directory unique to each node containing data element name first parts and data element name second parts, the second directory identifying a location within the network where the data element corresponding to the multi-part name is stored; referencing data elements by multi-part name from referencing nodes and in the referencing nodes storing binding information relating multi¬ part names to data elements by: i) accessing the first directory to identify the node containing data element names having the first name part; ii) accessing the second directory in the identified node to identify a location in the network where the referenced multi-part name data element is stored; iii) storing in the referencing node the location identified in the second directory as binding information for the referenced data element name; and for subsequent references by the referencing node to the referenced data element name, retrieving the referenced data element from the location defined in the binding information. 30. The method of claim 29 wherein the step of retrieving the referenced data element further comprises: comparing the data element name at the location identified by the binding information with the referenced name and if a match is not found, replacing the binding information by repeating steps i) through iii) . 31. The method of claim 29 further comprising reporting an error message if one of the first and second data element name parts is not found on the network. 32. The method recited in claim 22, wherein the distributed network system is a facilities management system and further comprising the step of at least monitoring at least one control process. 33. An apparatus for locating data in a distributed network system having nodes communicating on a the network comprising: means for receiving a download of data elements and corresponding unique data element names to addressable data element locations in at least one of the nodes; processing means in the nodes for referencing the data elements by name from referencing nodes; storage means in the nodes for storing binding information relating names and corresponding data element locations by searching the network for the location of a data element the first time the data element is referenced by the referencing node and storing by name in the referencing node the location of the referenced data element; and the processing means identifying the location of the data element from the binding information and retrieving the data element from the location defined in the binding information for subsequent references by the referencing node to stored data element names. 34. The apparatus recited in claim 33, wherein the processing means retrieving a data element further comprises: means for comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, again searching the network for a new location of the data element corresponding to the name referenced by the referencing node; means for, if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with the new binding information including the new location of the data element and producing an error message if the name referenced by the referencing node is not found. 35. The apparatus recited in claim 33, wherein the binding information comprises a single binding information table on the storage means in each of the referencing nodes. 36. The apparatus recited in claim 35, wherein the single binding information table comprises stored entries corresponding to data element names, the entries being made the first time the application and features reference the data element names. 37. The apparatus recited in claim 35, further comprising: storage means in each referencing node for storing an index of references to the unique data element names from applications and features in the referencing node and a corresponding location in the binding information table; and wherein the processing means in the nodes having means for accessing the binding information of the data element names referenced by the applications and features by accessing the location in the binding table identified by the index for the referenced data element names. 38. The apparatus recited in claim 33, wherein the processing means comprises: means for comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, searching the node identified in the binding information for another location within the identified node of the data element name; means for, if the data element name is not found at said another location in the node identified in the binding information, searching remaining nodes on the network for a new location of the data element corresponding to the name referenced by the referencing node; means for, if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with new binding information including an updated location of the data element and producing an error message if the name referenced by the referencing node is not found. 39. An apparatus for locating data in a distributed network system having nodes with processing means and information storage means comprising: means in the nodes for downloading from a processor data elements and corresponding unique multi-part data element names having at least a first part and a second part to addressable locations in at least one of the nodes; means in the nodes for broadcasting to all the nodes in the network a common first directory containing data element name first parts, the directory identifying the nodes on which names having the first parts have been downloaded; and wherein the storage means stored in each node has at least a second directory unique to each node containing data element name first parts and data element name second parts, the second directory identifying a location within the network where the data element corresponding to the multi-part name is stored; and wherein the processing means in the nodes references data elements by multi-part name from referencing nodes and in the referencing nodes storing binding information relating multi-part names to data elements by: i) accessing the first directory to identify the node containing data element names having the first name part; ii) accessing the second directory in the identified node to identify a location in the network where the referenced multi-part name data element is stored; iii) storing in the referencing node the location identified in the second directory as binding information for the referenced data element name; and wherein for subsequent references by the referencing node to the referenced data element name, the referenced data element is retrieved from the location defined in the binding information. 40. An apparatus as recited in claim 33, wherein the network comprises a facilities management system having means for at least monitoring at least one control process. 41. A storage medium including stored indicia of a plurality of operating instructions locating data in a distributed network system having nodes with processing means and information storage means, the instructions including instructions for: downloading from a processor data elements and corresponding unique data element names to addressable data element locations in at least one of the nodes; referencing the data elements by name from the referencing nodes; storing binding information relating names and corresponding data element locations by searching the network for the location of a data element the first time the data element is referenced by the referencing node and storing by name in the referencing node the location of the referenced data element; for subsequent references by the referencing node to stored data element names, identifying the location of the data element from the binding information and retrieving the data element from the location defined in the binding information. 42. Stored indicia as recited in claim 41, wherein the instructions for retrieving a data element further include instructions for: comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, again searching the network for a new location of the data element corresponding to the name referenced by the referencing node; if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with the new binding information including the new location of the data element and producing an error message if the name referenced by the referencing node is not found. 43. Stored indicia as recited in claim 41, wherein the instructions for storing the binding information further include instructions for building a single binding information table in each referencing node. 44. Stored indicia as recited in claim 43, wherein the instructions for building the binding table further include instructions for: storing a table of data element names referenced by applications and software features in the node; and storing the binding information in the table the first time the application and features reference the data element name. 45. Stored indicia as recited in claim 42, wherein the instructions further include instructions for: storing in each reference node an index of references to the unique data element names from applications and features in the referencing node and a corresponding location in the binding information table; and accessing the binding information of the data element names referenced by the applications and features by accessing the location in the binding table identified by the index for the referenced data element names. 46. Stored indicia as recited in claim 41, wherein the instructions further include instructions for: comparing the data element name at the location identified in the binding information with the name referenced by the referencing node and if a match is not found, searching the node identified in the binding information for another location within the identified node of the data element name; if the data element name is not found at said another location in the node identified in the binding information, searching remaining nodes on the network for a new location of the data element corresponding to the name referenced by the referencing node; if the name referenced by the referencing node is found, replacing the binding information relating the data element name to the location of the data element with new binding information including an updated location of the data element and producing an error message if the name referenced by the referencing node is not found. 47. A storage medium including stored indicia of a plurality of operating instructions for locating data in a distributed network system having nodes with processing means and information storage means, the instructions including instructions for: downloading from a processor data elements and corresponding unique multi-part data element names having at least a first part and a second part to addressable locations in at least one of the nodes; broadcasting to all the nodes in the network a common first directory containing data element name first parts, the directory identifying the nodes on which names having the first parts have been downloaded; storing in each node at least a second directory unique to each node containing data element name first parts and data element name second parts, the second directory identifying a location within the network where the data element corresponding to the multi-part name is stored; referencing data elements by multi-part name from referencing nodes and in the referencing nodes storing binding information relating multi¬ part names to data elements by: i) accessing the first directory to identify the node containing data element names having the first name part; ii) accessing the second directory in the identified node to identify a location in the network where the referenced multi-part name data element is stored; iii) storing in the referencing node the location identified in the second directory as binding information for the referenced data element name; and for subsequent references by the referencing node to the referenced data element name, retrieving the referenced data element from the location defined in the binding information. 48. Stored indicia as recited in claim 41, wherein the distributed network system is a facilities management system and wherein the instructions further include instructions for at least monitoring at least one control process. 49. A method of accessing nodes on a configured system of nodes forming at least one network, the nodes being interconnected by at least one communication link, with a non-configured device not part of the network, comprising the steps of: connecting the non-configured device to a port of a first con igured node configured on the system at a first location defined by a subnet and a local address; assigning a network address having a first portion including the first location and a drop identifier portion to the non-configured device; transmitting messages having the assigned network address as a source indicator from the non-configured device to configured destination nodes configured on the system at locations defined by subnets, local addresses, and drop identifiers; receiving responses from the destination nodes at the first node according to the first portion of the assigned network address; transmitting the responses to the non- configured device through the port specified by the drop identifier portion of the assigned address. 50. The method of claim 49 further comprising the step of: routing the messages between the non- configured device and the destination nodes along routes for message traffic between the first configured node and the configured destination nodes. 51. The method of claim 50 further comprising the steps of: storing at each node a routing table, the table having an entry for each destination node address, the entries of the table defining the next address along paths from each possible source node to destination nodes. . 52. The method of claim 49 further comprising the steps of: predetermining the routes at network configuration time and storing portions of the predetermined routes in sequences of nodes as a series of network addresses, each network address defining a next location along a path from a source node to the destination node. 53. The method of claim 52 further comprising the step of storing a static routing table at each node, the static routing table having an entry for each destination node address, the entries of the table defining the next address along paths from each possible source node to destination nodes. 54. The method of claim 52 further comprising the step of storing the predetermined route portion in a table in a central processor and accessing the table to define the route. 55. The method of claim 50 further comprising the step of: adaptively routing messages between the non-configured device and the destination nodes along routes for message traffic between the first configured node and the configured destination nodes determined by a dynamic routing strategy sensitive to message traffic throughout the system. 56. The method recited in claim 49, wherein the network comprises a facilities management system further comprising the steps of monitoring and controlling at least one process. 57. A networked system of configured nodes allowing access to the system by non-configured devices comprising: a plurality of nodes, each of the nodes having means for storing a network address defining a location of the node on the system, and at least one of the nodes having at least one port for connecting a non-configured device; means for interconnecting the nodes over at least one communications link to form a network; means for storing routing information, the routing information having network addresses defining paths from configured source nodes to configured destination nodes; means for routing messages between the configured nodes via the paths; means for identifying a non-configured device connected to said at least one port of the said at least one configured node and for passing messages between processes programmed into the configured nodes and processes programmed into the non-configured device. 58. The apparatus of claim 57 wherein the means for identifying non-configured devices comprises: means in each configured node for assigning, storing and communicating to said at least one non-configured device connected to said at least one port of the node a portion of a network address comprising a subnet, a local address and a Drop ID identifying the port of the configured node connected to the non-configured device. 59. The apparatus of claim 58 wherein the network address further comprises a process identifier appended by the non-configured device. 60. The apparatus of claim 57 or claim 58 wherein the means for storing routing information comprises means for storing routing tables, each said routing table having entries for each destination node, the entries of the table defining a next node address along the path from a source node to the destination nodes. 61. The apparatus of claim 57 or claim 58 wherein the means for routing comprises means in each configured node for decoding a network address of each message received by the configured node and means for: passing a data portion of the message to a process in the configured node, if the decoded address identifies the configured node as the destination; passing a data portion of the message to the port, if the decoded address identifies a non- configured device connected to the configured node as the destination; passing the message to a next node address defined in the table, if the decoded address does not include the decoding configured node. 62. The apparatus of claim 60 wherein the means for storing the routing information comprises memory means in each node. 63. The apparatus of claim 60 wherein the means for storing the routing information comprises centralized memory means in a single node. 64. The apparatus of claim 60 wherein the tables comprises static routing tables each said table having entries defining predetermined paths between configured nodes. 65. The apparatus of claim 60 wherein the tables comprise adaptive routing tables, each said table having variable entries determined by a dynamic routing strategy sensitive to message traffic throughout the system. 66. The apparatus recited in claim 57 wherein the network comprises a facilities management system and further comprising means for monitoring and controlling at least one process. 67. A storage medium including stored indicia of a plurality of operating instructions for accessing nodes on a configured system of nodes forming at least one network, the nodes being interconnected by at least one communication link, with a non-configured device not part of the network, the instructions including instructions for: connecting the non-configured device to a port of a first configured node configured on the system at a first location defined by a subnet and a local address; assigning a network address having a first portion including the first location and a drop identifier portion to the non-configured device; transmitting messages having the assigned network address as a source indicator from the non-configured device to configured destination nodes configured on the system at locations defined by subnets, local addresses, and drop identifiers; receiving responses from the destination nodes at the first node according to the first portion of the assigned network address; transmitting the responses to the non- configured device through the port specified by the drop identifier portion of the assigned address. 68. Stored indicia as recited in claim 65 wherein the instructions further include instructions for: routing the messages between the non- configured device and the destination nodes along routes for message traffic between the first configured node and the configured destination nodes. 69. Stored indicia as recited in claim 68 wherein the instructions further include instructions for: storing at each node a routing table, the table having an entry for each destination node address, the entries of the table defining the next address along paths from each possible source node to destination nodes. 70. Stored indicia as recited in claim 67 wherein the instructions further include instructions for: predetermining the routes at network configuration time and storing portions of the predetermined routes in sequences of nodes as a series of network addresses, each network address defining a next location along a path from a source node to the destination node. 71. Stored indicia as recited in claim 70 wherein the instructions further include instructions for storing a static routing table at each node, the static routing table having an entry for each destination node address, the entries of the table defining the next address along paths from each possible source node to destination nodes. 72. Stored indicia as recited in claim 70 wherein the instructions further include instructions for storing the predetermined route portion in a table in a central processor and accessing the table to define the route. 73. Stored indicia as recited in claim 68 wherein the instructions further include instructions for adaptively routing messages between the non-configured device and the destination nodes along routes for message traffic between the first configured node and the configured destination nodes determined by a dynamic routing strategy sensitive to message traffic throughout the system. 74. Stored indicia as recited in claim 67 wherein the network comprises a facilities management system and the instructions further include instructions for monitoring and controlling at least one process. 75. A method of controlling access to data items available on a network having nodes with processing and storage means, comprising the steps of: i) storing in the storage means a value of each data item requested on the network at a storage time; ii) storing in the storage means an aging time value for each requested data item, the aging time value defining a data valid time period measured from the storage time; iii) during the data valid period after the storage time, servicing requests for the data item with the value of the data item stored at the storage time, until a data invalid time defined by an end of the data valid time period; and iv) at a first request for the data item after the data invalid time, storing a new value of the data item and repeating steps i) through iii) . 76. The method of claim 75 further comprising the steps of: producing the data items in slave nodes having data acquisition means; transferring the values of the data items from the slave nodes to corresponding master nodes and storing the values of the data items in the master nodes; and storing the aging time values corresponding to the stored data items in the master nodes. 77. The method of claim 76 further comprising the step of storing data item values in the master nodes as entries in stored data tables, each entry having an associated aging time. 78. The method of claim 75 further comprising transmitting the aging time to a network entity requesting a data item and preventing further requests over the network from the entity until the data invalid time. 79. The method recited in claim 75 wherein the network forms a facilities management system and further comprising the steps of monitoring and controlling at least one process. 80. An apparatus for controlling access to data items generated by operational units and slave controllers controlled by computerized nodes comprising: processing means in each node for requesting and retrieving requested data items from the operational units and slave controllers; storage means or storing the requested data items and corresponding storage times; means for storing an aging time value for each requested data item, the aging time value defining a data valid time period measured from the storage time; means for during the data valid period after the storage time, servicing requests for the data item with the value of the data item stored at the storage time, until a data invalid time defined by an end of the data valid time period. 81. The apparatus recited in claim 80 wherein the storage means for the requested data items and the aging times comprise data tables stored in memories of the nodes retrieving the data items. 82. The apparatus recited in claim 80 further comprising means for transmitting the aging time to a network entity requesting a data item and preventing further requests over the network from the entity until the data invalid time. 83. The apparatus recited in claim 80 wherein the network forms a facilities management system, further comprising means for at least monitoring at least one control process. 84. A storage medium including stored indicia of a plurality of operating instructions controlling access to data items on a network, the instructions including instructions for: i) storing a value of each data item requested on the network at a storage time; ii) storing an aging time value for each requested data item, the aging time value defining a data valid time period measured from the storage time; iii) during the data valid period after the storage time, servicing requests for the data item with the value of the data item stored at the storage time, until a data invalid time defined by an end of the data valid time period; and iv) at a first request for the data item after the data invalid time, storing a new value of the data item and repeating steps i) through iii) . 85. Stored indicia as recited in claim 8 wherein the instructions further includ instructions for: producing the data items in slave node having data acquisition means; transferring the values of the dat items from the slave nodes to corresponding maste nodes and storing the values of the data items i the master nodes; and storing the aging time value corresponding to the stored data items in the maste nodes. 86. Stored indicia as recited in claim 8 wherein the instructions further includ instructions for storing data item values in th master nodes as entries in stored data tables, eac entry having an associated aging time. 87. Stored indicia as recited in claim 8 wherein the instructions further includ instructions for transmitting the aging time to network entity requesting a data item and preventin further requests over the network from the entit until the data invalid time. 88. A method of allocating high reliabilit data to processes executed by processing means i nodes communicating with each other over a network comprising the steps of: storing in memory means in the node expected ranges of values of identifiable dat elements passed between programmed high leve features stored in the memory means and executed b the processing means in the nodes; receiving the identifiable data elements at the features and comparing the received data elements with the stored expected ranges corresponding to the identifiable data elements; if a received data element is within the expected range, tagging the data element with an indicator that the data element is reliable and using the data element in further processing of the feature; if a received data element is an unreliable data element because it is not within the expected range, seeking an alternate reliable source of the unreliable data element by additional processing identifying alternate sources of data elements and substituting a value within the expected range obtained from an alternate source. 89. The method recited in claim 88 wherein the step of seeking alternate sources of the data element further comprises searching directories in the nodes for alternate storage locations storing the data element and for alternate sensors producing the data element. 90. The method recited in claim 88 wherein the step of seeking alternate sources of the data element further comprises processing in the nodes to derive substitute data for the unreliable data element from other data available on the network. 91. The method recited in claim 88 further comprising: determining in a processing means performing the feature if a previous value of an unreliable data element is useful if no alternate source of the unreliable data element is found; and if useful, preventing replacement of the previous reliable value in the feature and storing an indication of the prevention, and if not useful, indicating to the feature that the data element is unreliable. 92. The method recited in claim 88 wherein the network forms a facilities management system further comprising the step of at least monitoring at least one control process. 93. An apparatus allocating high reliability data to processes executed by processing means in nodes communicating with each other over a network, comprising: memory means in the nodes for storing expected ranges of values of identifiable data elements passed between programmed high level features stored in the memory means and executed by the processing means in the nodes; means for transferring the identifiable data elements to the features and comparing the received data elements with the stored expected ranges corresponding to the identifiable data elements; means for tagging the data element with an indicator that the data element is reliable if a received data element is within the expected range, and for transferring the data element for further processing by the feature; processing means for seeking an alternate reliable source of a received data element if the received data element is an unreliable data element because it is not within the expected range, the processing means identifying alternate sources of data elements and substituting a value within the expected range obtained from an alternate source. 94. An apparatus as recited in claim 93 wherein the processing means for seeking alternate sources of the data element further comprises means for searching directories in the nodes for alternate storage locations storing the data element and for alternate sensors producing the data element. 95. An apparatus as recited in claim 93 wherein the processing means seeking alternate sources of the data element derives substitute data for the unreliable data element from other data available on the network. 96. An apparatus as recited in claim 93 wherein a processing means performing the feature determines if a previous value of an unreliable data element is useful if no alternate source of the unreliable data element is found and, if useful prevents replacement of the previous reliable data element and records an indication of the replacement and, if not useful, indicates that the data element is unreliable to the feature. 97. An apparatus as recited in claim 93 wherein the network forms a facilities management system further comprising means for at least monitoring at least one process. 98. A storage medium including stored indicia of a plurality of operating instructions allocating data to processes executed by processing means in nodes communicating with each other over a network, the instructions including instructions for: storing in memory means in the nodes expected ranges of values of identifiable data elements passed between programmed high level features stored in the memory means and executed by the processing means in the nodes; receiving the identifiable data elements at the features and comparing the received data elements with the stored expected ranges corresponding to the identifiable data elements; if a received data element is within the expected range, tagging the data element with an indicator that the data element is reliable and using the data element in further processing of the feature; if a received data element is an unreliable data element because it is not within the expected range, seeking an alternate reliable source of the unreliable data element by additional processing identifying alternate sources of data elements and substituting a value within the expected range obtained from an alternate source. 99. Stored indicia as recited in claim 98 wherein the instructions for seeking alternate sources of the data element further include instructions for searching directories in the nodes for alternate storage locations storing the data element and for alternate sensors producing the data element. 100. Stored indicia as recited in claim 98 wherein the instructions for seeking alternate sources of the data element further include instructions for substituting data for the unreliable data element from other data available on the network. 101. Stored indicia as recited in claim 98 wherein the instructions further include instructions for: determining in a processing means performing the feature if a previous value of an unreliable data element is useful if no alternate source of the unreliable data element is found; and if useful, preventing replacement of the previous reliable value in the feature and storing an indication of the prevention, and if not useful, indicating to the feature that the data element is unreliable. 102. Stored indicia as recited in claim 98, wherein the network forms facilities management system further including instructions for at least monitoring at least one control process. 103. A method of updating variables and data in a distributed network having a plurality of nodes comprising the steps of: at known times issuing requests to processors in target nodes from high level processing features in other nodes to inform the high level features of changes in values of specified data elements; storing the requests in a memory means in the target nodes; comparing in the other nodes the known times with periodically issued time stamps transmitted by the target nodes, the time stamps indicating most recent update times of the memory means in the target nodes, thereby determining if the requests by the other nodes remain effective in the target nodes at times after the known times. 104. The method of claim 103 further comprising the step of invalidating a said request if the time stamp is later than a corresponding said known time and transmitting a new request from the other node to a corresponding target node to inform the high level feature of changes in specified data elements. 105. The method of claim 104 further comprising the steps of: determining if any of the requests is rejected because a corresponding data element is no longer found in a corresponding said target node; and identifying a new location of the data element. 106. The method of claim 103 wherein the network is a facilities management system further comprising at least monitoring at least one control process. 107. A storage medium including stored indicia of a plurality of operating instructions updating variables and data in a distributed network, said network having a plurality of nodes, the instructions including instructions for: at known times issuing requests from high level coded features in said nodes to coded processors stored in target nodes, to inform said high level features of changes in values of specified data elements; comparing said known times with periodically issued time stamps transmitted by said target nodes, said time stamps indicating most recent update times of memory means in said target nodes, said coded steps for comparing said known time thereby determining by said comparison if said requests remain effective in said target nodes at times after said known times. 108. Stored indicia as recited in claim 107 further including instructions for validating a said request if said time stamp is later than a corresponding said known time; and transmitting a new request from a said node to a corresponding target node to inform said high level feature of changes in specified data elements. 109. Stored indicia as recited in claim 108 further including instructions for: determining if any of said requests is rejected because a corresponding data element is not found in said target node; and executing a binding scheme to identify a new location of said data element. 110. Stored indicia as recited in claim 109 wherein the network is a facilities management system and including instructions for at least monitoring at least one control process. 111. An apparatus for updating variables and data in a distributed network having a plurality of nodes comprising: nodes having high level features issuing requests at known times to processors in target nodes to inform said nodes of changes in values of specified data elements; means for storing and processing said requests in said target nodes; processor means in said nodes for comparing said known times with periodically issued time stamps transmitted by said target nodes, said time stamps indicating most recent update times of said memory means in said target nodes. 112. The apparatus of claim 111 wherein said processor means further comprises: means for detecting if a said time stamp is later than a corresponding said known time and for invalidating a corresponding request. 113. The apparatus of claim 112 wherein said processor means further comprises: means for transmitting a new request from a said node to a corresponding target node to inform said high level function of changes in specified data elements. 114. The apparatus of claim 113 wherein said processor means further comprises: means for determining if any of said requests is rejected because a corresponding data element is not found on a corresponding said target node; and means for executing a binding scheme to identify a new location of said data element. 115. The apparatus of claim 111 wherein said network is a facilities management system and further comprising means for at least monitoring at least one control process. 116. A method of accessing data in an automated processing system comprising the steps of: processing information for high level software functions in at least one intermediate object processing level having identified objects stored in a storage means; defining each identified object in said intermediate processing level by at least one corresponding attribute; storing in a storage means at least one attribute for a first said identified object, said attribute identifying another identified object having at least one attribute; obtaining from said other identified object at least one said attribute further defining parameters of said first object; and routing said attributes of said other object to said first object. 117. The method recited in claim 116 wherein said other identified object is a point obtaining its attribute values from data gathered by operational units and said first identified object is a pseudo point. 118. The method recited in claim 116 wherein said automated processing system is a facilities management system, the method comprising at least monitoring at least one control process. 119. An apparatus for accessing data in an automated processing system comprising the steps of: a processor processing information for high level software functions in at least one intermediate object processing level having identified objects stored in a storage means, the processing means defining each identified object in said intermediate processing level by at least one corresponding attribute; storage means for storing at least one attribute for a first said identified object, said attribute identifying another identified object having at least one attribute; the processing means having means for retrieving from said other identified object at least one said attribute further defining parameters of said first object; and means for routing said attributes of said other object to said first object. 120. The apparatus recited in claim 119 wherein said other identified object is a point obtaining its attribute values from data gathered by operational units and said first identified object is a pseudo point. 121. The apparatus recited in claim 119 wherein the automated processing system comprises a facilities management system, comprising means for at least monitoring at least one control process. 122. A storage medium including stored indicia of a plurality of operating instructions accessing data in an automated processing system the instructions including instructions for: processing information for high level software functions in at least one intermediate object processing level having identified objects stored in a storage means; defining each identified object in said intermediate processing level by at least one corresponding attribute; storing in a storage means at least one attribute for a first said identified object, said attribute identifying another identified object having at least one attribute; obtaining from said other identified object at least one said attribute further defining parameters of said first object; and routing said attributes of said other object to said first object. 123. Stored indicia as recited in claim 122 wherein said other identified object is a point obtaining its attribute values from data gathered by operational units and said first identified object is a pseudo point. 124. Stored indicia as recited in claim 122 wherein the automated processing system is a facilities management system further including instructions for at least monitoring at least one control process. 125. A method of limiting energy consumption of a network having: loads controlled by nodes communicating over the network, the nodes having storage and processing means, the method comprising the steps of: storing in the storage means of the nodes, load restoration characteristics of loads controlled by the nodes; executing processing of a high level software feature in the processing means of a node to limit energy consumption of the network, and subsequently transmitting over the network commands to shed particular loads controlled by other nodes; executing predefined load shedding processing in the nodes controlling the particular nodes using a local software object having a data base manager and processes and attributes stored in a data base in the node storage means; under control of the local software object restoring the shed loads independently of load shed commands under circumstances defined by the attributes of the local software object. 126. The method recited in claim 125 comprising: storing in the storage means of nodes having energy consumption limiting features, load tables containing energy consumption values for loads controlled by the nodes on the network; determining in the processing means an amount of desired energy consumption reduction; and comparing energy consumption values in the stored tables with currently active loads to identify at least one load to be shed to meet the desired reduction. 127. The method recited in claim 125 wherein the feature limiting energy consumption of the network limits overall energy consumption to a substantially constant level. 128. The method recited in claim 125 wherein the local software object restores a load after receiving a restore command initiated by an operator. 129. The method recited in claim 128 wherein the feature limiting energy consumption limits energy consumption by the network to predetermined limits corresponding to stored predetermined time periods. 130. The method recited in claim 129 wherein the stored predetermined time periods include sliding time intervals including a future interval during which energy consumption is assumed to remain constant and past interval during which energy consumption was monitored, the method comprising the further step of: identifying an amount of desired load shed required in the future interval to maintain total energy consumption below a desired level for the interval defined by the past interval and future interval. 131. The method recited in claim 125 wherein the network is a facilities management system comprising at least monitoring at least one control process. 132. An apparatus for limiting energy - consumption of a network having: loads controlled by nodes communicating over the network, the nodes having storage and processing means, the method comprising the steps of: storage means in the nodes, for storing load restoration characteristics of loads controlled by the nodes; processing means in the nodes for executing processing of a high level software feature in a node to limit energy consumption of the network, and subsequently transmitting over the network commands to shed particular loads controlled by other nodes; the processing means executing predefined load shedding processing in the nodes controlling the particular nodes by using a local software object having a data base manager and processes and attributes stored in a data base in the node storage means; the processing means under control of the local software object restoring the shed loads to a operation independently of load shed commands under circumstances defined by the attributes of the local software object. 133. The apparatus recited in claim 132 comprising: means in the storage means of the nodes having energy consumption limiting features, for storing load tables containing energy consumption values for loads controlled by the nodes on the network; means in the processing means for determining an amount of desired energy consumption reduction; and means in the processing means for comparing energy consumption values in the stored tables with currently active loads to identify at least one load to be shed to meet the desired reduction. 134. The apparatus recited in claim 133 wherein the feature limiting energy consumption of the network limits overall energy consumption to a substantially constant level. 135. The apparatus recited in claim 132 wherein the local software object restores a load after receiving a restore command initiated by an operator. 136. The apparatus recited in claim 135 wherein the feature limiting energy consumption limits energy consumption by the network to predetermined limits corresponding to stored predetermined time periods. 137. The apparatus recited in claim 136 wherein the stored predetermined time periods include sliding time intervals including a future interval during which energy consumption is assumed to remain constant and past interval during which energy consumption was monitored, the processing means comprising means for: identifying an amount of desired load shed required in the future interval to maintain total energy consumption below a desired level for the interval defined by the past interval and future interval. 138. The apparatus recited in claim 132 wherein the 'network is a facilities management system comprising means for at least monitoring at least one control process. 139. A storage medium including a stored indicia of a plurality of operating instructions limiting energy consumption of a network having: loads controlled by nodes communicating over the network, the nodes having storage and processing means, the instructions including instructions for: storing in the storage means of he nodes, load restoration characteristics of loads controlled by the nodes; executing processing of a high level software feature in the processing means of a node to limit energy consumption of the network, and subsequently transmitting over the network commands to shed particular loads controlled by other nodes; executing predefined load shedding processing in the nodes controlling the particular nodes using a local software object having a data base manager and processes and attributes stored in a data base in the node storage means; under control of the local software object restoring the shed loads to a operation independently of load shed commands under circumstances defined by the attributes of the local software object. 140. Stored indicia as recited in claim 139 further including instructions for: storing in the storage means of nodes having energy consumption limiting features, load tables containing energy consumption values for loads controlled by the nodes on the network; determining in the processing means an amount of desired energy consumption reduction; and comparing energy consumption values in the stored tables with currently active loads to identify at least one load to be shed to meet the desired reduction. 141. Stored indicia as recited in claim 139 wherein the feature limiting energy consumption of the network includes instructions for limiting overall energy consumption to a substantially constant level. 142. Stored indicia as recited in claim 139 wherein the local software object includes instructions for restoring a load after receiving a restore command initiated by an operator. 143. Stored indicia as recited in claim 142 wherein the feature limiting energy consumption includes instructions for limiting energy consumption by the network to predetermined limits corresponding to stored predetermined time periods. 144. Stored indicia as recited in claim 143 wherein the stored predetermined time periods include sliding time intervals including a future interval during which energy consumption is assumed to remain constant and part interval during which energy consumption was monitored, the instructions including: identifying an amount of desired load shed required in the future interval to maintain total energy consumption below a desired level for the interval defined by the past interval and future interval. 145. Stored indicia as recited in claim 139 wherein the network is a facilities management system including instructions for at least monitoring at least one process. 146. A method of distributing a plurality of elements defining a system in an automated processing network having a plurality of nodes comprising the steps of: for each system defined, identifying one of said nodes as a corresponding directory node; storing in a memory means of the directory node a directory of identified objects corresponding to said system; storing in said memory means at least one entry corresponding to each directory, the entries identifying memory locations on said network where said corresponding identified objects are stored; updating said directories with revised directories as identified objects are relocated in the network, said updating of said directories further comprising the steps of: transmitting from an object a presence indicating message to its last known corresponding directory and determining if said object is present in said updated directory; and reporting an error if said object is not found. 147. The method recited in claim 146 further comprising the step of maintaining in the memory means of each said directory node a reference identification table identifying all objects defined in the node, said reference identification table identifying to a directory manager destinations of messages routed to objects. 148. A method of distributing a plurality of elements defining a system in an automated processing network having a plurality of nodes comprising the steps of: for each system defined identifying one of said nodes as a corresponding directory node; storing in a memory means of the directory node a directory of identified objects corresponding to said system; storing in said memory means at least one entry corresponding to each directory, the entries identifying memory locations on said network where said corresponding identified objects are stored; updating said directories with revised directories as identified objects are relocated in the network said updating of said directories further comprising the steps of: transmitting from a directory messages to the objects in the directory and observing responses from the objects; and reporting an error for each of said objects not found. 149. The method recited in claim 148 further comprising the step of maintaining in memory of each said directory node a reference identification table, said reference identification table identifying to a directory manager if an object corresponding to a message received by the node is present in the node. 150. The method recited in claim 146 wherein the network is a facilities management system further comprising at least monitoring at least one control process. 151. A storage medium including stored indicia of a plurality of operating instructions defining specified systems from a plurality of elements distributed among nodes connected to form an automated processing network, the instructions comprising instructions for: identifying said nodes as directory nodes for specified systems defined on said network; storing in memory means of the directory nodes, directories of identified objects corresponding to said specified systems; storing in said memory means at least one entry in each directory, each entry identifying memory locations on said network where corresponding identified objects are stored; updating said directories with revised directories as identified objects are relocated in the network, said coded steps updating of said directories further comprising: transmitting from an object a presence indicating message to its last known corresponding directory; determining if said object is present in said updated directory; and reporting an error if said object is not found. 152. Stored indicia as recited in claim 151 further including instructions for maintaining in memory each said directory node a reference identification table identifying all objects defined in the node, said reference identification table identifying to a directory manager destinations of messages routed to objects. 153. A storage medium including stored indicia of a plurality of operating instructions distributing a plurality of elements defining a system in an automated processing network having a plurality of nodes the instructions including instructions for: for each system defined, identifying one of said nodes as a corresponding directory node; storing in a memory means of the directory node a directory of identified objects corresponding to said system; storing in said memory means at least one entry corresponding to each directory, the entries identifying memory locations on said network where said corresponding identified objects are stored; updating said directories with revised directories as identified objects are relocated in the network, said updating of said directories further including instructions for: transmitting from an object a presence indicating message to its last known corresponding directory and determining if said object is present in said updated directory; and reporting an error if said object is not found. 154. Stored indicia recited in claim 153 further including instructions for maintaining in memory of each said directory node a reference identification table, said reference identification table identifying to a directory manager if an object corresponding to a message received by the node is present in the node. 155. Stored indicia as recited in claim 151 wherein the system is a facilities management system further including instructions for at least monitoring at least one process. 156. An automated processing network having a plurality of elements distributed on a plurality of nodes the elements in the nodes definining systems, comprising: for each system defined, means for identifying one of said nodes as a corresponding directory node; memory means in the directory node for storing a directory of identified objects corresponding to said systems; means in the memory means for storing at least one entry corresponding to each directory, the entries identifying memory locations on said network where said corresponding identified objects are stored; processing means for updating said directiories with revised directiories as identified objects are relocated in the network, said updating of said directories further comprising the steps of: means for transmitting from an object a presence indicating message to its last known corresponding directory and determining if said object is present in said updated directory; and means for reporting an error if said object is not found. 157. The apparatus recited in claim 156 further comprising means for maintaining in memory of each said directory node a reference identification table identifying all objects defined in the node, said reference identification table identifying to a directory manager destinations of messages routed to objects. 158. An automated processing network having a plurality of elements distributed on a plurality of nodes, the elements defining systems comprising: for each system defined, means for identifying one of said nodes as a corresponding directory node; memory means in the directory node for storing a directory of identified objects corresponding to said system; means in the memory means for storing at least one entry corresponding to each directory, the entries identifying memory locations on said network where said corresponding identified objects are stored; processing means for updating said directions with revised directions as identified objects are relocated in the network, further comprising: means for transmitting from an object a presence indicating message to its last known corresponding directory and determining if said object is present in said updated directory; and reporting an error if said object is not found. 159. The apparatus recited in claim 158 further comprising means for maintaining in memory of each said directory node a reference identification table, said reference identification table identifying to a directory manager if an object corresponding to a message received by the node is present in the node. 160. The apparatus recited in claim 156 wherein the system is a facilities management system comprising means for at least monitoring at least one control process. 161. A method of reporting messages among processing nodes interconnected to form a network comprising the steps of: a) storing report routers in memory means of the nodes, the report routers identifying locations of preferred input/output tasks stored in the nodes for messages indicating changing states of points connected to the nodes; b) storing input/output tasks in nodes identified by the report routers, the input/output tasks identifying at least one destination output device for the messages received; c) routing each change of state message indicating changing states of points connected to the nodes to locations identified by a report router in a node communicating with a changing point ; d) processing each of the messages in the input/output task stored at the location identified by the report router to determine if the message can be routed to a destination output device controlled by the node storing the input/output task; e) if the message can be routed to one of the identified destination output devices, routing the message and signalling the report router that the message has been successfully transferred, f) if the message cannot be routed to one of the identified destination output devices, routing the message to another report router, the other report router being stored in the node having the input/output task and identifying at least one alternative processing location for the message; g) repeating steps d) , e) , and f) until all possible destination output destination devices are exhausted. 162. The method recited in claim 161 further comprising the step of storing messages which cannot be successfully routed to a destination output device in save files in memory means of nodes originating the messages. 163. The method recited in claim 161 wherein the network is a facilities management system, comprising at least monitoring at least one control process. 164. A storage medium including stored indicia of a plurality of operating instructions for reporting messages among processing nodes interconnected to form a network, the operating instructions including instructions for: a) storing report routers in memory means of the nodes, the report routers identifying locations of preferred input/output tasks stored in the nodes for messages indicating changing states of points connected to the nodes; b) storing input/output tasks in nodes identified by the report routers, the input/output tasks identifying at least one destination output device for the messages received; c) routing each change of state message indicating changing states of points connected to the nodes to locations identified by a report router in a node communicating with a changing point; d) processing each of the messages in the input/output task stored at the location identified by the report router to determine if the message can be routed to a destination output device controlled by the node storing the input/output task; e) if the message can be routed to one of the identified destination output devices, routing the message and signalling the report router that the message has been successfully transferred, f) if the message cannot be routed to one of the identified destination output devices, routing the message to another report router, the other report router being stored in the node having the input/output task and identifying at least one alternative processing location for the message; g) repeating steps d) , e) , and f) until all possible destination output destination devices are exhausted. 165. Stored indicia as recited in claim 164, the instructions further include instructions for storing messages which cannot be successfully routed to a destination output device in save files in memory means of nodes originating the messages. 166. Stored indicia as recited in claim 164 wherein the network is a facilities management system, further including instructions for at least monitoring at least one control process. 167. An apparatus for reporting messages among processing nodes interconnected to form a network comprising: a) in memory means in the nodes for storing report routers the report routers identifying locations of preferred input/output tasks stored in the nodes for messages indicating changing states of points connected to the nodes; b) means in the nodes for storing input/output tasks identified by the report routers, the input/output tasks identifying at least one destination output device for the messages received; c) means for routing each change of state message indicating changing states of points connected to the nodes to locations identified by a report router in a node communicating with a changing point; d) means for processing each of the messages in the input/output task stored at the location identified by the report router to determine if the message can be routed to a destination output device controlled by the node storing the input/output task; and e) if the message can be routed to one of the identified destination output devices, routing the message and signalling the report router that the message has been successfully transferred, f) if the message cannot be routed to one of the identified destination output devices, routing the message to another report router, the other report router being stored in the node having the input/output task and identifying at least one alternative processing location for the message; g) repeating steps d) , e) , and f) until all possible destination output destination devices are exhausted. 168. The method recited in claim 167 further comprising memory means of nodes originating the messages for storing messages which cannot be successfully routed to a destination output device in save files. 169. The method recited in claim 167 wherein the network is a facilities management system, comprising means for at least monitoring at least one control process. 170. A method of synchronizing time among a plurality of automated processing nodes communicating over a network comprising: transmitting a time initialization message from a system time manager node and subsequently monitoring elapsed time in the system time manager node and in nodes receiving the time initialization message; at predefined time initialization intervals in each of the nodes testing a stored indicator to determine if the node is the system time manager node and - if the node is the system time manager node, transmitting a new time synchronization message; - if the node is not the system time manager node, determining if a new time synchronization message has been received and resetting the time in the node to a time specified in the new time initialization message. 171. The method recited in claim 170, wherein a node which is not the system time manager node fails to receive a new time initialization message comprising transmitting from the node a time initialization from the node a time initialization message thereby synchronizing remaining nodes on the network. 172. The method recited in claim 171, wherein the network is a facilities management system comprising at least monitoring at least one process. 173. A method of synchronizing data bases stored in storage means of a plurality of nodes communicating over a network, the method comprising the steps of: storing in the storage means of each node a time stamp indicating a most recent time of updating a data base stored in the node; periodically transmitting from each node the time stamp stored in the node; receiving the transmitted time stamps at each node and comparing each received time stamp with the time stamp stored; requesting the node transmitting the time stamp to transmit its data base to the node receiving the time stamp if the time stamp received is later than the time stamp stored. 174. The method recited in claim 173, comprising storing in a non-volatile memory of each node an identifier of an archive device and initializing the data bases of the nodes from the archive device. 175. The method recited in claim 173, wherein at least one node controls at least one slave device further comprising: reporting a time stamp from a slave device coming on line to a corresponding node; in the node comparing reported time stamps with the time stamp in the node and if the node has a time stamp later than a reported time stamp, transmitting at least a portion the data base in the node to the slave device. 176. The method recited in claim 173, wherein the network is a facilities management system, comprising at least monitoring at least one control process. 177. An apparatus for synchronizing time among a plurality of automated processing nodes communicating over a network comprising: processing means for in the nodes transmitting a time initialization message from a system time manager node and subsequently monitoring elapsed time in the system time manager node and in nodes receiving the time initialization message; the processing means in each of the nodes testing at predefined time initialization intervals a stored indicator to determine if the node is the system time manager node and means for: - if the node is the system time manager node, transmitting a new time synchronization message; - if the node is not the system time manager node, determining if a new time synchronization message has been received and resetting the time in the node to a time specified in the new time initialization message. 178. The apparatus as recited in claim 177, wherein a node which is not the system time manager node fails to receive a new time initialization message comprising means for transmitting from the node a time initialization from the node a time initialization message thereby synchronizing remaining nodes on the network. 179. The apparatus as recited in claim 177, wherein the network is a facilities management system comprising means for at least monitoring at least one control process. 180. An apparatus for synchronizing data bases stored in storage means of a plurality of nodes communicating over a network, comprising: means in the storage means of each node for storing a time stamp indicating a most recent time of updating a data base stored in the node; means for periodically transmitting from each node the time stamp stored in the node; means for receiving the transmitted time stamps at each node and comparing each received time stamp with the time stamp stored; means in each node for requesting the node transmitting the time stamp to transmit its data base to the node receiving the time stamp if the time stamp received is later than the time stamp stored. 181. The apparatus as recited in claim 180, comprising storing in a non-volatile memory means in each node for storing an identifier of an archive device and means for initializing the data bases of the nodes from the archive device. 182. The apparatus as recited in claim 180, wherein at least one node controls at least one slave device further comprising: means for receiving a reported time stamp from a slave device coming in line to a corresponding node; means for comparing in the node reported time stamps with the time stamp in the node and if the node has a time stamp later than a reported time stamp, transmitting at least a portion of the data base in the node to the slave device. 183. The apparatus as recited in claim 180, wherein the network is a facilities management system, comprising means for at least monitoring at least one control process. 184. A storage medium including stored indicia of a plurality of operating instructions synchronizing time among a plurality of automated processing nodes communicating over a network the instructions including instructions for: transmitting a time initialization message from a system time manager node and subsequently mounting elapsed time in the system time manager node and in nodes receiving the time initialization message; at predefined time initialization intervals in each of the nodes testing a stored indicator to determine if the node is the system time manager node and - if the node is the system time manager node, transmitting a new time synchronization message; if the node is not the system time manager node, determining if a new time synchronization message has been received and resetting the time in the node to a time specified in the new time initialization message. 185. Stored indicia as recited in claim 184, wherein a node which is not the system time manager node fails to receive a new time initialization message including instructions for transmitting from the node a time initialization from the node a time initialization message thereby synchronizing remaining nodes on the network. 186. Stored indicia as recited in claim 184, wherein the network is a facilities management system including instructions for at least monitoring at least one control process. 187. A storage medium including stored indicia of a plurality of instructions synchronizing data bases stored in storage means of a plurality of nodes communicating over a network, the instructions including instructions for: storing in the storage means of each node a time stamp indicating a most recent time of updating a data base stored in the node; periodically transmitting from each node the time stamp stored in the node; receiving the transmitted time stamps at each node and comparing each received time stamp with the time stamp stored; requesting the node transmitting the time stamp to transmit its data base to the node receiving the time stamp if the time stamp received is later than the time stamp stored. 188. Stored indicia as recited in claim 187, including instructions for storing in a non-volatile memory of each node an identifier of an archive device and for initializing the data bases of the nodes from the archive device. 189. Stored indicia as recited in claim 187, wherein at least one node controls at least one slave device further including instructions for: reporting a time stamp from a slave device coming in line to a corresponding node; in the node comparing reported time stamps with the time stamp in the node and if the node has a time stamp later than a reported time stamp, transmitting at least a portion the data base in the node to the slave device. 190. Stored indicia as recited in claim 187, wherein the network is a facilities management system, including instructions for at least monitoring at least one control process. 191. A method of downloading information stored in an archiving device to a destination node, the destination node being one of a plurality of nodes communicating on a network, in the absence of a routing table in the destination node, the method comprising the steps of: transmitting at least one message from the archive device to at least one intermediate node having a routing table stored in a storage means; transferring control of message routing to the intermediate nodes and passing the messages through the intermediate nodes to the destination node; and acknowledging receipt of the download by transmitting an acknowledge message from the receiving node to the intermediate node immediately passing the message and routing the acknowledgement through routing tables defined in the intermediate nodes. 192. A method of routing an information download request from a requesting node without a routing table operating on a network having a plurality of nodes to an archive device containing requested download data, the method comprising the steps of: storing in a non-volatile memory of each node an identity an NC initiator, the NC initiator being another node which initiates a download request for the node; storing in each node an archive device identifier; downloading data from an archive device to at least one of the nodes, the nodes being NC initiators for other nodes; requesting a download from a node without a routing table by transmitting a request to the NC initiator for the node; if the NC initiator for the node has been downloaded with a routing table, transmitting the request to one of the archive device and another node in the plurality of nodes, the other node being an intermediate node, the intermediate nodes having tables further routing the request along a path to the download device defined stored routing tables. 193. The method recited in claim 192, further comprising sequentially downloading nodes by downloading a first node as an NC initiator and downloading a second node by reading from a storage means of the second node an identifier of the irst node as the NC initiator for the second node and routing the second node download request through the first node; subsequently downloading a third node by reading an Identifier of one of the first and second nodes from a storage means in the third node as the NC initiator for the third node and routing the download request to the stored NC initiator; subsequently downloading other nodes by reading an identifier of a previously downloaded node as an NC initiator for the node and routing the download request through the corresponding previously downloaded node. 194. The method as recited in claim 192, wherein the first download is initiated by the archive device. 195. The method recited in claim 192, wherein the first download is accomplished by a direct request from the node to the download device identified in the node storage means. 196. The method recited in claim 192, wherein the plurality of nodes from a facilities management system further comprising at least monitoring at least one control process. 197. An apparatus for downloading information stored in an archiving device to a destination node, the destination node being one of a plurality of nodes communicating on a network, in the absence of a routing table in the destination node, comprising: means for transmitting at least one message from the archive device to at least one intermediate node having a routing table stored in a storage means; means for transferring control of message routing to the intermediate nodes and passing the messages through the intermediate nodes to the destination node; and means for acknowledging receipt of the download by transmitting an acknowledge message from the receiving node to the intermediate node immediately passing the message and routing the acknowledgement through routing tables defined in the intermediate nodes. 198. An apparatus for routing an information download request from a requesting node without a routing table operating on a network having a plurality of nodes to an archive device containing requested download data, comprising: a non-volatile memory, in each node for sharing an identity an NC initiator, the NC initiator being another node which initiates a download request for the node; means for storing in each node an archive device identifier; processing means for downloading data from an archive device to at least one of the nodes, the nodes being NC initiators for other nodes; processing means for requesting a download from a node without a routing table by transmitting a request to the NC initiator for the node and if the NC initiator for the node has been downloaded with a routing table, the processing means transmitting the request to one of the archive device and another node in the plurality of nodes, the other node being an intermediate node, the intermediate nodes having tables further routing the request along a path to the download device defined stored routing tables. 199. The apparatus recited in claim 198, wherein a processing means in a first node downloads the first node as an NC initiator and a processing means in a second node downloads the second node by reading from a storage means of the second node an identifier of the first node as the NC initiator for the second node and routes the second node download request through the first node; processing means in a third node which reads an Identifier of one of the first and second nodes from a storage means in the third node as the NC initiator for the third node and routes the download request to the stored NC initiator; processing means in each of the other of the plurality of nodes, the processing means reading an identifier of a previously downloaded node as an NC initiator for the node and routing the download request through the corresponding previously downloaded node. 200. The apparatus as recited in claim 198, wherein the first download is initiated by the archive device. 201. The apparatus recited in claim 198, wherein the first download is accomplished by a direct request from the processing means in node to the download device identified in the node storage means. 202. The apparatus recited in claim 198, wherein the plurality of nodes from a facilities management system further comprises means for at least monitoring at least one control process. 203. A storage medium including stored indicia of a plurality of operating instructions downloading information stored in an archiving device to a destination node, the destination node being one of a plurality of nodes communicating on a network, in the absence of a routing table in the destination node, the instructions including instructions for: transmitting at least one message from the archive device to at least one intermediate node having a routing table stored in a storage means; transferring control of message routing to the intermediate nodes and passing the messages through the intermediate nodes to the destination node; and acknowledging receipt of the download by transmitting an acknowledge message from the receiving node to the intermediate node immediately passing the message and routing the acknowledgement through routing tables defined in the intermediate nodes. 204. A storage medium including stored indicia of a plurality of operating instructions routing an information download request from a requesting node without a routing table operating on a network having a plurality of nodes to an archive device containing requested download data, the instructions including instructions for: storing in a non-volatile memory of each node an identity an NC initiator, the NC initiator being another node which initiates a download request for the node; storing in each node an archive device identifier; downloading data from an archive device to at least one of the nodes, the nodes being NC initiators for other nodes; requesting a download from a node without a routing table by transmitting a request to the NC initiator for the node; if the NC initiator for the node has been downloaded with a routing table, transmitting the request to one of the archive device and another node in the plurality of nodes, the other node being an intermediate node, the intermediate nodes having tables further routing the request along a path to the download device defined stored routing tables. 205. Stored indicia as recited in claim 204, further including instructions for sequentially downloading nodes by downloading a first node as an NC initiator and downloading a second node by reading from a storage means of the second node an identifier of the first node as the NC initiator for the second node and routing the second node download request through the first node; subsequently downloading a third node by reading an Identifier of one of the first and second nodes from a storage means in the third node as the NC initiator for the third node and routing the download request to the stored NC initiator; subsequently downloading other nodes by reading an identifier of a previously downloaded node as an NC initiator for the node and routing the download request through the corresponding previously downloaded node. 206. Stored indicia as recited in claim 204, wherein the first download is initiated by the archive device. 207. Stored indicia as recited in claim 204, including instructions in the first node wherein the first download is accomplished by a direct request from the node to the download device identified in the node storage means. 208. Stored indicia as recited in claim 204, wherein the plurality of nodes from a facilities management system the instructions further including instructions for at least monitoring at least one control process. 209. A method of reporting a summary of objects, the objects being named data elements stored in storage means in a plurality of locations in a network having a plurality of nodes communicating with each other comprising the steps of: generating in a high level feature of a report destination node a directive specifying an object identifier and attribute selection criteria, identifying a node on the network having a stored object directory specifying locations on the network of all objects identified by the object identifier ; retrieving into the node having the object directory from locations specified by the object directory stored objects corresponding to the object identifier; comparing the retrieved objects against the specified attribute selection criteria in a processing means in the node having the object directory; discarding all objects not meeting the selection criteria and saving in a buffer objects meeting the selection criteria until all retrieved objects have been tested; and subsequently, serially transmitting the saved objects to the destination node. 210. The method recited in claim 209 wherein the network is a facilities management system further comprising at least monitoring at least one control process. 211. A storage medium including stored indicia of a plurality of operating instructions for reporting a summary of objects of objects stored in storage means in a plurality of locations in a network having a plurality of nodes communicating with each other, the instruction comprising instructions for: generating in a high level feature of a report destination node a directive specifying an object identifier and attribute selection criteria, identifying a node on the network having a stored object directory specifying locations on the network of all objects identified by the object identifier ; retrieving into the node having the object directory from locations specified by the object directory stored objects corresponding to the object identifier; comparing the retrieved objects against the specified attribute selection criteria in a processing means in the node having the object directory; discarding all objects not meeting the selection criteria and saving in a buffer objects meeting the selection criteria until all retrieved objects have been tested; and subsequently, serially transmitting the saved objects to the destination node. 212. Stored indicia as recited in claim 211 wherein the network is a facilities management system further including instructions for at least monitoring at least one control process. 213. An apparatus for reporting a summary of objects, the objects being named data elements stored in storage means in a plurality of locations in a network having a plurality of nodes communicating with each other comprising: processing means in the nodes for generating in a high level feature of a report destination node a directive specifying an object identifier and attribute selection criteria, the processing means further identifying a node on the network having a stored object directory specifying locations on the network of all objects identified by the object identifier; the processing means further retrieving into the node having the object directory from locations specified by the object directory stored objects corresponding to the object identifier; the processing means further comparing the retrieved objects against the specified attribute selection criteria in a processing means in the node having the object directory; the processing means discarding all objects not meeting the selection criteria and saving in a buffer objects meeting the selection criteria until all retrieved objects have been tested; and the processing means subsequently, serially transmitting the saved objects to the destination node. 214. A method of controlling a process loop of a control system operating on at least one computerized node having processing and storage means, the method comprising the steps of: a) storing a Proportional and Integral & Derivative (PID) loop software object in the storage means of at least one of the nodes, the PID loop object having a data base manager and a stored data base of attributes and processes for providing proportional and integral and derivative control of a process loop in the control system; and b) under control of the PID loop reading data identifying a setpoint of the controlled process; - reading input data from a controlled process loop, conditioning the read data with coefficients corresponding to each input and determining a value of feedback variable from the read inputs and the coefficients; executing a stored PID process of proportional, integral and derivative control of manipulated variables of the controlled process loop, the PID process generating outputs referencing the manipulated variables as attributes of objects to set the feedback variable within a predefined range of the setpoint. 215. The method of claim 214 wherein the predefined range of the setpoint is stored as an attribute of the PID object. 216. The method of claim 214 wherein the read data comprises individual references to attributes, each attribute being one of an actual value and a reference to an attribute of another object. 217. The method recited in claim 214 comprising reading the offset value and in the processing means offsetting an output of the PID process by an amount and direction corresponding to the read offset value. 218. The method recited in claim 214 comprising reading high and low saturation limits and in the processing means preventing a PID output from issuing an output outside the high and low saturation limits. 219. The method recited in claim 214 further comprising sampling the input data at times defined by measuring a sample period stored as an attribute of the PID object. 220. The method recited in claim 219 comprising sampling input data for each of a plurality of instances of the PID loop on a priority basis such that each PID loop is sampled within 15% of its sample period. 221. The method recited in claim 214 wherein the PID outputs have integral, proportional and derivative terms. 222. The method recited in claim 221 wherein an integral time for integral control is stored as an attribute of the PID object and the integration terms of PID outputs are calculated over the integral time. 223. The method recited in claim 222 wherein the integral time is an amount of time taken for an integral term of an output to equal a proportional term of an output if a constant error is indicated by a difference between the feedback and the setpoint. 224. The method recited in claim 223 wherein the integral terms are defined by: Iterm(t)=( (T/Itime) * Pterm(t) +(1-T/Itime) + Iterm(t-1) . 225. The method recited in claim 221 wherein a proportion band coefficient for proportional control is stored and retrieved as an attribute of the PID loop object and the proportion term is defined by: Pterm(t) = 100 * E(t)/Pband. 226. The method recited in claim 221 wherein a derivative weight is stored and retrieved as an attribute of the PID loop object and wherein the derivative term sensitizes the PID loop object to a rate of change of the feedback value. 227. The method recited in claim 226 wherein the derivative term is defined by: Dterm(t) = Dweight * { (Itime/4 * T) * 100/Pband * (feedbac (t) feedback(t-l))}. 228. The method recited in claim 221 wherein the outputs further include a hysteresis compensation term. 229. The method recited in claim 228 wherein a hysteresis compensation value is stored and retrieved as an attribute in the PID loop object, and is the amount of hysteresis encounted between the output and the feedback. 230. The method of claim 228 further comprising reading an offset value and offsetting one output of the PID process by an amount and direction corresponding to the read offset value. 231. The method recited in claim 230 wherein the PID outputs are defined as: OUT(t) = Pterm(t) + Iterm(t-l) + Dterm(t) + Offset(t) + Hysteresis compensation(t) . 232. The method recited in claim 214 wherein the database manager interfaces to other objects in the node which read and write data to and from and issue commands to a process control loop, schedules processing of each of a plurality of instances of the PID loop, and executes subsidiary processing. 233. The method recited in claim 214 wherein the PID loop object detects one of an override condition for all outputs receiving commands from the PID loop object and an auxiliary signal switch enable set condition, comprising: determining a proportional term of the output and; when one of the conditions changes, executing a bumpless transfer by setting the output to a value of an immediately proceeding output modified by Pterm when the conditions changed. 234. The method recited in claim 214 wherein the PID loop object reads an auxiliary signal enable attribute stored in the storage means and in one condition of the auxiliary signal attribute routes a PID process output to subsidiary processing and in a second condition routes an auxiliary signal to subsidiary processing. 235. The method recited in claim 234 wherein the PID loop object reads a filter weight attribute stored in the storage means and filters a PID output value being one of the PID process output and the auxiliary signal to a filter output attribute defined by: previous filter value + ((1/filter weight) * (PID output value - previous filter value) ) wherein the previous filter value is the filter output attribute from an immediately preceding iteration. 236. The method recited in claim 235 wherein the PID loop object compares the filter output attribute a high/low signal, reads an H/L select attribute stored in the storage means and in a first state of the H/L select attribute stores a greater of the output filter attribute and the high/low signal in an HO attribute and in a second state of the H/L select attribute stores lower of the output filter attribute and the high/low signal in the HO attribute. 237. The method recited in claim 214 wherein the PID loop object sets an output to a last reliable state where an input becomes unreliable. 238. The method recited in claim 214 wherein the PID loop object sets an output to a last reliable state when a mathematical error occurs in PID processing. 239. The method recited in claim 214 wherein the PID loop object outputs represent percents of full scale deflection to drive the controlled variable toward the setpoint. 240. An apparatus for controlling a process loop of a control system operating on at least one computerized node having processing and storage means, comprising: a) storage means in at least one of the nodes for storing a Proportional and Integral & Derivative (PID) loop software object the PID loop object having a data base manager and a stored data base of attributes and processes for providing proportional and integral and derivative control of a process loop in the control system; and b) processing means for, under control of the PID loop, reading data identifying a setpoint of the controlled process - reading input data from a controlled process loop, conditioning the read data with coefficients corresponding to each input and determining a value of feedback variable from the read inputs and the coefficients; executing a stored PID process of proportional, integral and differential control of manipulated variables of the controlled process loop, the PID process generating outputs referencing the manipulated variables as attributes of objects to set the feedback variable within a predefined range of the setpoint. 241. The apparatus recited in claim 240 wherein the predefined range of the setpoint is stored as an attribute of the PID object. 242. The apparatus of claim 240 wherein the read data comprises individual references to attributes, each attribute being one of an actual value and a reference to an attribute of another object. 243. The apparatus recited in claim 240 comprising means in the processing means reading the offset value and in the processing means offsetting an output of the PID process by an amount and direction corresponding to the read offset value. 244. The apparatus recited in claim 240 comprising means in the processing means for reading high and low saturation limits and in the processing means preventing a PID output from issuing an output outside the high and low saturation limits. 245. The apparatus recited in claim 240 further comprising sampling means in the processing means for sampling the input data at times defined by measuring a sample period stored as an attribute of the PID object. 246. The apparatus recited in claim 245 comprising sampling input data for each of a plurality of instances of the PID loop on a priority basis such that each PID loop is sampled within 15% of its sample period. 247. The apparatus recited in claim 240 wherein the PID outputs have integral, proportional and derivative terms. 248. The apparatus recited in claim 247 wherein an integral time for integral control is stored as an attribute of the PID object and the integration terms of PID outputs are calculated by the processing means over the integral time. 249. The apparatus recited in claim 248 wherein the integral time is an amount of time taken for an integral term of an output to equal a proportional term of an output if a constant error is indicated by a difference between the feedback and the setpoint. 250. The apparatus recited in claim 249 wherein the integral terms are defined by: Iterm(t)=((T/Itime) * Pterm(t)) +1-T/Itime) + Iterm(t-1) . 251. The apparatus recited in claim 247 wherein a proportion band coefficient for proportional control is stored and retrieved as an attribute of the PID loop object and the proportion term is defined by: Pterm(t) = 100 * E(t)/Pband. 252. The apparatus recited in claim 247 wherein a derivative weight is stored and retrieved as an attribute of the PID loop object and wherein in the processing means the derivative term sensitizes the PID loop object to a rate of change of the feedback value. 253. The apparatus recited in claim 252 wherein the derivative term is defined by: Dterm(t) = Dweight * {(Itime/4 *T) * 100/Pband * (feedback(t) - feedbac (t- 1))}. 254. The apparatus recited in claim 252 wherein the outputs further include a hysteresis compensation term. 255. The apparatus recited in claim 254 wherein a hysteresis compensation value is stored in the storage means and retrieved by the processing means as an attribute in the PID loop object, and is the amount of hysteresis encounted between the output and the feedback. 256. The apparatus of claim 254 wherein an offset value is read and one output of the PID process is offset by an amount and direction corresponding to the read offset value. 257. The apparatus recited in claim 256 wherein the PID outputs are defined as: OUT(t) = Pterm(t) + Iterm(t-1) + Dterm(t) + Offset(t) + Hysteresis compensation(t) . 258. The apparatus recited in claim 240 wherein the database manager in the processing means interfaces to other objects in the node which read and write data to and from and issue commands to a process control loop, schedules processing of each of a plurality of instances of the PID loop, and executes subsidiary processing. 259. The apparatus recited in claim 240 wherein the PID loop object detects one of an override condition for all outputs receiving commands from the PID loop object and an auxiliary signal switch enable set condition, comprising: means in the processing means for determining a proportional term of the output and; - when one of the conditions changes, executing a bumpless transfer by setting the output to a value of an immediately proceeding output modified by Pterm when the conditions changed. 260. The apparatus recited in claim 240 wherein the PID loop object reads an auxiliary signal enable attribute stored in the storage means and in one condition of the auxiliary signal attribute routes a PID process output to subsidiary processing and in a second condition routes an auxiliary signal to subsidiary processing. 261. The apparatus recited in claim 240 wherein the PID loop object reads a filter weight attribute stored in the storage means and filters a PID output value being one of the PID process output and the auxiliary signal to a filter output attribute defined by: previous filter value + ((1/filter weight) * (PID output value - previous filter value) ) wherein the previous filter value is the filter output attribute from an immediately preceding iteration. 262. The apparatus recited in claim 261 wherein the PID loop object compares the filter output attribute a high/low signal, reads an H/L select attribute stored in the storage means and in a first state of the H/L select attribute stores a greater of the output filter attribute and the high/low signal in an HO attribute and in a second state of the H/L select attribute stores lower of the output filter attribute and the high/low signal in the HO attribute. 263. The apparatus recited in claim 240 wherein the PID loop object sets an output to a last reliable state where an input becomes unreliable. 264. The apparatus recited in claim 240 wherein the PID loop object sets an output to a last reliable state when a mathematical error occurs in PID processing. 265. The apparatus recited in claim 240 wherein the PID loop object outputs are percents of full scale deflection to drive the controlled variable toward the setpoint. 266. A storage medium including stored indicia of a plurality of operating instructions controlling a process loop of a control system operating on at least one computerized node having processing and storage means, the instructions including instructions for: a) storing a Proportional plus Integral plus Derivative (PID) loop software object in the storage means of at least one of the nodes, the PID loop object having a data base manager and a stored data base of attributes and processes for providing proportional and integral and derivative control of a process loop in the control system; and b) under control of the PID loop reading data identifying a setpoint of the controlled process - reading input data from a controlled process loop, conditioning the read data with coefficients corresponding to each input and determining a value of feedback variable from the read inputs and the coefficients; executing a stored PID process of proportional, plus integral plus derivative control of manipulated variables of the controlled process loop, the PID process generating outputs referencing the manipulated variables as attributes of objects to set the feedback variable within a predefined range of the setpoint. 267. Stored indicia as recited in claim 266 wherein the predefined range of the setpoint is stored as an attribute of the PID object. 268. Stored indicia as recited claim 266 wherein the read data comprises individual references to attributes, each attribute being one of an actual value and a reference to an attribute of another object. 269. Stored indicia as recited in claim 266 including instructions for reading the offset value and in the processing means offsetting an output of the PID process by an amount and direction corresponding to the read offset value. 270. Stored indicia as recited in claim 266 including instructions for reading high and low saturation limits and in the processing means preventing a PID output from issuing an output outside the high and low saturation limits. 271. Stored indicia as recited in claim 266 further including instructions for sampling the input data at times defined by measuring a sample period stored as an attribute of the PID object. 272. Stored indicia as recited in claim 271 including instructions for sampling input data for each of a plurality of instances of the PID loop on a priority basis such that each PID loop is sampled within 15% of its sample period. 273. Stored indicia as recited in claim 266 wherein the PID outputs have integral, proportional and derivative terms. 274. Stored indicia as recited in claim 266 including instructions wherein an integral time for integral control is stored as an attribute of the PID object and the integration terms of PID outputs are calculated over the integral time. 275. Stored indicia as recited in claim 274 including instructions wherein the integral time is an amount of time taken for an integral term of an output to equal a proportional term of an output if a constant error as indicated by a difference between the feedback and the setpoint. 276. Stored indicia as recited in claim 275 including instructions wherein the integral terms are defined by: Iterm(t)=((T/Itime) *Pterm(t)) + (1-T/Itime) + Iterm(t-1) . 277. Stored indicia as recited in claim 273 including instructions wherein a proportion band coefficient for proportional control is stored and retrieved as an attribute of the PID loop object and the proportion term is defined by: Pterm(t) = 100 * E(t)/Pband. 278. Stored indicia as recited in claim 273 including instructions wherein a derivative weight is stored and retrieved as an attribute of the PID loop object and wherein the derivative term sensitizes the PID loop object to a rate of change of the feedback value. 279. Stored indicia as recited in claim 278 including instructions wherein the derivative term is defined by: Dterm(t) = Dweight * { (Itime/4T) * (100/Pband) * (feedback(t) - feedback(t- 1))}. 280. Stored indicia as method recited in claim 273 including instructions wherein the outputs further include a hysteresis compensation term. 281. Stored indicia as recited in claim 280 including instructions wherein a hysteresis compensation value is stored and retrieved as an attribute in the PID loop object, and is the amount of hysteresis encounted between the output and the feedbac . 282. Stored indicia as recited in claim 280 further including instructions for reading an offset value and offsetting one output of the PID process by an amount and direction corresponding to the read offset value. 283. Stored indicia as recited in claim 282 including instructions wherein the PID outputs are defined as: OUT(t) = Pterm(t) + Iterm(t-l) + Dterm(t) + Offset(t) + Hysteresis compensation(t) . 284. Stored indicia as recited in claim 266 including instructions wherein the database manager interfaces to other objects in the node which read and write data to and from and issue commands to a process control loop, schedules processing of each of a plurality of instances of the PID loop, and executes subsidiary processing. 285. Stored indicia as recited in claim 266 including instruction wherein the PID loop object detects one of an override condition for all outputs receiving commands from the PID loop object and an auxiliary signal switch enable set condition, comprising: - determining a proportional term of the output and; - when one of the conditions changes, executing a bumpless transfer by setting the output to a value of an immediately proceeding output modified by Pterm when the conditions changed. 286. Stored indicia as recited in claim 266 including instructions wherein the PID loop object reads an auxiliary signal enable attribute stored in the storage means and in one condition of the auxiliary signal attribute routes a PID process output to subsidiary processing and in a second condition routes an auxiliary signal to subsidiary processing. 287. Stored indicia as recited in claim 286 including instructions wherein the PID loop object reads a filter weight attribute stored in the storage means and filters a PID output value being one of the PID process output and the auxiliary signal to a filter output attribute defined by: previous filter value + ((1/filter weight) * (PID output value - previous filter value) ) wherein the previous filter value is the filter output attribute from an immediately preceding iteration. 288. Stored indicia as recited in claim 287 including instructions wherein the PID loop object compares the filter output attribute a high/low signal, reads an H/L select attribute stored in the storage means and in a first state of the H/L select attribute stores a greater of the output filter attribute and the high/low signal in an HO attribute and in a second state of the H/L select attribute stores lower of the output filter attribute and the high/low signal in the HO attribute. 289. Stored indicia as recited in claim 266 including instructions wherein the PID loop object sets an output to a last reliable state where an input becomes unreliable. 290. Stored indicia as recited in claim 266 including instructions wherein the PID loop object sets an output to a last reliable state when a mathematical error occurs in PID processing. 291. Stored indicia as recited in claim 266 including instructions wherein the PID loop object outputs are percents of full scale deflection to drive the controlled variable toward the setpoint. 292. A method of controlling a control system process loop responsive to at least one input control variable the input control variable being sensitive to a state of an output device in the process loop, the method comprising the steps of: storing a desired setpoint in a storage means; - monitoring states of the output device and providing a control variable which is a time function of the states of the output device; receiving the control variable at a process controller; - generating a manipulated variable in the process controller and transmitting the manipulated variable to the output device, the manipulated variable driving the output device to cause the control variable to approach the setpoint; - monitoring values of the control variable in a process monitor and determining if the control variable is not within a predetermined reliable range; when the control variable is outside the reliable range, substituting a backup value for the manipulated variable, the backup value being generated independently of a current value of the control variable in a fault tolerant controller. 293. The method recited in claim 292 wherein the process controller, the process monitor and the fault tolerant controller are software objects stored in a storage means of a computerized node, the software objects having a database manager and a database of processes and attributes. 294. The method recited in claim 292 wherein the process monitor periodically stores entries indicating maximum and minimum values of a process output used in determining the manipulated variable; and stores a maximum of a plurality of errors, each error equal to an absolute value of a difference between the setpoint and the control variable. 295. The method recited in claim 294 wherein the process monitor periodically determines if the process is saturated by comparing the process output with stored saturation limits. 296. The method recited in claim 295 wherein the fault tolerant controller periodically tests a reliability status of the control variable and if reliable determines if the process is saturated. 297. The method recited in claim 294 wherein the process monitor periodically compares a first difference of the maximum and minimum values of the process output with a second difference between stored high and low output values and increments a number of deviations of the first difference beyond predetermined fractions of the second difference. 298. The method recited in claim 297 wherein the process monitor sets a stable flag to a first state if the number of deviations for any of the predetermined fractions exceeds a predetermined value or if an error is outside a predetermined error band stored in a storage means and otherwise to a second state. 299. The method recited in claim 298 wherein the stable flag is set to the first state if the number of consecutive deviations for any of the predetermined fraction exceeds the predetermined value. 300. The method recited in claim 298 wherein the fault tolerant controller periodically tests a reliability status of the control variable and, if reliable, determines a status of the stable flag; and wherein, if the stable flag is in the second state, the fault tolerant controller replaces predefined stored variables with new reliable values of the variables. 301. The method recited in claim 292 wherein the fault tolerant controller tests a status of the control variable and, if not reliable, replaces predefined stored variables with current values from the process loop. 302. The method recited in claim 301 wherein the fault tolerant controller stores as an effectiveness variable a stored reference value of the manipulated variable, the effectiveness variable being limited to a predetermined range less than an entire range of the manipulated variable. 303. The method of claim 302 wherein the backup value is determined by the fault tolerant controller to be: MV1 0 + EFF * (MV2-MV2 + 100% * (SP-CV) + 10 0 % * j- (EFF-100%) * (PV1-PV1 0 ) ] PB 0 - 100% * t (EFF * (PV2-PV2 ] PB 0 wherein EFF is the effectiveness value, MV2 is a current value of a secondary manipulated variable, MV2„ is a stored reference value of the secondary manipulated variable, PB 0 is a stored reference proportional band, PV1 0 and PV1 are stored and current first process variables respectively and PV2 0 and PV2 are stored and current second process variables, respectively. 304. The method recited in claim 292 wherein the backup value and manipulated variable are routed to a switch means, and wherein the switch means switches an output between the manipulated variable and the backup according to a flag generated by the fault tolerant controller. 305. A storage medium including stored indicia of a plurality of operating instructions controlling a control system process loop responsive to at least one input control variable the input control variable being sensitive to a state of an output device in the process loop wherein the instructions include instructions for: storing a desired setpoint in a storage means; monitoring states of the output device and providing a control variable which is a time function of the states of the output device; receiving the control variable at a process controller; generating a manipulated variable in the process controller and transmitting the manipulated variable to the output device, the manipulated variable driving the output device to cause the control variable to approach the setpoint; monitoring values of the control variable in a process monitor and determining if the control variable is not within a predetermined reliable range; when the control variable is outside the reliable range, substituting a backup value for the manipulated variable, the backup value being generated independently of a current value of the control variable in a fault tolerant controller. 306. Stored indicia as recited in claim 305 wherein the process controller, the process monitor and the fault tolerant controller are software objects stored in a storage means of a computerized node, the software objects having a database manager and a database of processes and attributes. 307. Stored indicia as recited in claim 305 including instructions wherein the process monitor periodically stores entries indicating maximum and minimum values of a process output used in determining the manipulated variable; and stores a maximum of a plurality of errors each error equal to an absolute value of a difference between the setpoint and the control variable. 308. Stored indicia as recited in claim 307 including instructions wherein the process monitor periodically determines if the process is saturated by comparing the process output with stored saturation limits. 309. Stored indicia as recited in claim 307 including instruction wherein the fault tolerant controller periodically tests a reliability status of the control variable and, if reliable, determines if the process is saturated. 310. Stored indicia as recited in claim 309 including instructions wherein the process monitor periodically compares a first difference of the maximum and minimum values of the process output with a second difference between stored high and low output values and increments a number of deviations of the first difference beyond predetermined fractions of the second difference. 311. Stored indicia as recited in claim 310 including instructions wherein the process monitor sets a stable flag to a first state if the number of deviations for any of the predetermined fractions exceeds a predetermined value or if an error is outside a predetermined error band stored in a storage means and otherwise to a second state. 312. Stored indicia as recited in claim 310 including instructions wherein the stable flag is set to the first state if the number of consecutive deviations for any of the predetermined fractions exceeds the predetermined value. 313. Stored indicia as recited in claim 311 including instructions wherein the fault tolerant controller periodically tests a reliability status of the control variable and, if reliable, determines a status of the stable flag; and wherein, if the stable flag is in the second state, the fault tolerant controller replaces predefined stored variables with new reliable values of the variables. 314. Stored indicia as recited in claim 305 including instructions wherein the fault tolerant controller tests a status of the control variable and, if not reliable, replaces predefined stored variables with current values from the process loop. 315. Stored indicia as recited in claim 314 including instructions wherein the fault tolerant controller stores as an effectiveness variable a value of the manipulated variable, the effectiveness variable being limited to a predetermined range less than an entire range of the manipulated variable. 316. Stored indicia as recited in claim 315 including instructions wherein the backup value is determined by the fault tolerant controller to be: MV1 0 + EFF * (MV2-MV2 0 ) + 100 % * (SP-CV) PB 0 + 1 00 % * [(EFF-100%) * (PV1-PV1 ] PB 0 - 100% * [ ( EFF * (PV2-PV2.) ] PB 0 wherein EFF is the effectiveness value, MV2 is a current value of a secondary manipulated variable, MV2 0 is a stored reference value of the secondary manipulated variable, PB 0 is a stored reference proportional band, PV1 0 and PV1 are stored and current first process variables respectively and PV2 0 and PV2 are stored and current second process variables. 317. Stored indicia as recited in claim 305 including instructions wherein the backup value and manipulated variable are routed to a switch means, and wherein the switch means switches are output between the manipulated variable and the backup according to a flag generated by the fault tolerant controller. 318. An apparatus for of controlling a control system process loop responsive to at least one input control variable the input control variable being sensitive to a state of an output device in the process loop comprising: means for storing a desired setpoint in a storage means; means for monitoring states of the output device and providing a control variable which is a time function of the states of the output device; - means for receiving the control variable at a process controller; the process controller generating a manipulated variable and transmitting the manipulated variable to the output device, the manipulated variable driving the output device to cause the control variable to approach the setpoint; process monitor means for monitoring values of the control variable and determining if the control variable is not within a predetermined reliable range; - fault tolerant controller means for, when the control variable is outside the reliable range, substituting a backup value for the manipulated variable, the backup value being generated independently of a current value of the control variable in the fault tolerant controller. 319. The apparatus recited in claim 318 wherein the process controller, the process monitor and the fault tolerant controller are software objects stored in a storage means of a computerized node, the software objects having a database manager and a database of processes and attributes. 320. The apparatus recited in claim 318 wherein the process monitor periodically stores entries indicating maximum and minimum values of a process output used in determining the manipulated variable; and stores a maximum of a plurality of errors each error equal to an absolute value of a difference between the setpoint and the control variable. 321. The apparatus recited in claim 320 wherein the process monitor periodically determines if the process is saturated by comparing the process output with stored saturation limits. 322. The apparatus recited in claim 321 wherein the fault tolerant controller periodically tests a reliability status of the control variable and if reliable determines if the process is saturated. 323. The apparatus recited in claim 321 wherein the process monitor periodically compares a first difference of the maximum and minimum values of the process output with a second difference between stored high and low output values and increments a number of deviations of the first difference beyond predetermined fractions of the second difference. 324. The apparatus recited in claim 323 wherein the process monitor sets a stable flag to a first state if the number of deviations for any of the predetermined fractions exceeds a predetermined value or if an error is outside a predetermined error band stored in a storage means and otherwise to a second state. 325. The apparatus recited in claim 324 wherein the process monitor sets the stable flag to the first state if the number of consecutive deviations for any of the predetermined fractions exceeds the predetermined value. 326. The apparatus recited in claim 324 wherein the fault tolerant controller periodically tests a reliability status of the control variable and, if reliable, determines a status of the stable flag; and wherein, if the stable flag is in the second state, the fault tolerant controller replaces predefined stored variables with new reliable values. 327. The apparatus recited in claim 318 wherein the fault tolerant controller tests a status of the control variable and, if not reliable, replaces predefined stored variables with current values from the process loop. 328. The apparatus recited in claim 327 wherein the fault tolerant controller stores as an effectiveness variable a stored value of the manipulated variable, the effectiveness variable being limited to a predetermined range less than an entire range of the manipulated variable. 329. The apparatus of claim 328 wherein the backup value is determined by the fault tolerant controller to be: MVl. + EFF * (MV2-MV2 + I 00 _% * (SP-CV) PB 0 + 1 00 % * [ (EFF-100%) * (PV1-PV1 ] PB 0 - 1 00 * [(EFF * (PV2-PV2 ] PB 0 wherein EFF is the effectiveness value, MV2 is a current value of a secondary manipulated variable, MV2 0 is a stored value of the secondary manipulated variable, PB 0 is a stored proportional band, PV1 0 and PV1 are stored and current first process variables respectively and PV2 0 and PV2 are stored and current second process variables. 330. The apparatus recited in claim 318 wherein the backup value and manipulated variable are routed to a switch means, and wherein the switch means switches are output between the manipulated variable and the backup according to a flag generated by the fault tolerant controller. 331. An apparatus for fault tolerant control of a closed loop control system comprising: control means, at least one output device, and feedback process means configured as a closed loop, wherein the control means has an output providing control signals to an input of an output device one of the signals being a manipulated variable, the output device provides signals to an input of the feedback process means, one of the signals being a related manipulated variable and wherein an output of the process feedback means provides signals to an input of the control means, one of the signals being a controlled feedback variable, the control means also receiving signals indicating a setpoint of the output device; means for monitoring the controlled feedback variable and for generating a loop fault indicative when the controlled feedback variable is not within a predetermined reliable range; means responsive to the loop fault indication for generating fault tolerant manipulated variable independent of the controlled feedback variable, the fault tolerant manipulated variable generating means comprising a means for monitoring at least one feedback process output other than the controlled feedback variable; means responsive to the loop fault indication for switching the input of the output device between the manipulated variable and the fault tolerant manipulated variable. 332. A computerized node having means for controlling at least one slave device connected to a slave device bus, the computerized node communicating with the slave devices over the bus and being optically isolated from the bus, the node comprising: an optical isolator connected between a signal line having outputs from the node and a line driver connected to a pair of signal lines of the bus; an optical isolator connected between a signal line receiving inputs for the node and a line receiver connected to the pair of signal lines of the bus; means responsive to a signal from the node for activating a transmit and receive mode, the pair of signal lines receiving signals from the bus in the receive mode and transmitting signals to the bus in the transmit mode; and means for biasing the signal lines to a predetermined voltage level to reduce sensitivity of the node to noise on the bus. 333. The computerized node recited in claim 332, wherein the means for activating the transmit and receive modes comprises an optical isolator responsive to a mode select signal. 334. The apparatus recited in claim 333 wherein the optical isolator responsive to the mode select signal has an output controlling operation of a line driver and receiver. 335. The apparatus recited in claim 334 comprising a buffer circuit between the output of the optical isolator responsive to the mode select signal and the line driver and receiver. 336. The apparatus recited in claim 332 comprising a retriggerable one shot responsive to the signal line having outputs, the one shot sourcing an uninterrupted current to an indicator during the transmit mode. 337. The apparatus recited in claim 332 comprising a retriggerable one shot responsive to the signal line receiving inputs, the one shot sourcing an uninterrupted current to an indicator during the receive mode. 338. The apparatus recited in claim 332 wherein the node has separate communications and digital power supplies. 339. The apparatus recited in claim 338 wherein the node has a power failure indicator responsive to both the communications and digital power supplies. 340. The apparatus recited in claim 339 wherein the indicator is driven by an optical isolator having a first portion connected to the communications supply and a second portion connected to the digital supply. 341. The apparatus recited in claim 340 wherein the first portion of the optical isolator is a light emitting portion and the second portion is a light receiving portion. 342. A method of reducing sensitivity of a computerized node to noise induced on a bus connected between the node and at least one slave device controlled by the node, the method comprising the steps of: connecting an optical isolator between a signal line having outputs from the node and a line driver connected to a pair of signal lines of the bus; connecting an optical isolator between a signal line receiving inputs for the node and a line receiver connected to the pair of signal lines of the bus; in response to a signal from the node activating a transmit and receive mode, the pair of signal lines receiving signals from the bus in the receive mode and transmitting signals to the bus in the transmit mode; and biasing the signal lines to a predetermined voltage level to reduce sensitivity of the node to noise on the bus. 343. The method recited in claim 332 wherein the transmit and receive modes are activated by an optical isolator responsive to a mode select signal. 344. The method recited in claim 343 wherein the optical isolator responsive to the mode select signal has an output controlling operation of a line driver and receiver. 345. The method recited in claim 344 comprising buffering in a buffer circuit the output of the optical isolator responsive to the mode select signal and the line driver and receiver. 346. The method recited in claim 342 comprising sourcing an uninterrupted current to an indicator during the transmit mode from an output a retriggerable one shot responsive to the signal line having outputs. 347. The method recited in claim 342 comprising sourcing an uninterrupted current to an indicator during the receive mode from an output of a retriggerable one shot responsive to the signal line receiving inputs. 348. The method recited in claim 342 wherein the node has separate communications and digital power supplies. 349. The apparatus recited in claim 348 wherein the node has a power failure indicator responsive to both the communications and digital power supplies. 350. The method recited in claim 339 wherein the indicator is driven by an optical isolator having a first portion connected to the communications supply and a second portion connected to the digital supply. 351. The method recited in claim 350 wherein the first portion of the optical isolator is a light emitting portion and the second portion is a light receiving portion. 352. The method recited in claim 162 further comprising routing messages from the same files to destination output devices which come on line. 353. The method recited in claim 352 wherein each report router is notified when destination output devices come on line and the report routers transmit messages to output devices specified. 354. The method recited in claim 162 wherein oldest and lowest priority messages are deleted from full save files when newer messages cannot be routed to destination output devices. 355. The apparatus recited in claim 213 wherein the network is a facilities management system further comprising means for at least monitoring at least one control process.

Inventors: BURKHARDT DENNIS E, DECIOUS GAYLON M, GARBE JAMES R, GOTTSCHALK DONALD A JR, HYZER SUSAN M, KOCH DAVID L, MADAUS PAUL W, MAGELAND OTTO M, NESLER CLAY G, PASCUCCI GREGORY A, RASMUSSEN DAVID E, SPACEK DAN J, STANDISH DARRELL E, STARK JAMES K, VAIRAVAN VAIRAVAN E, WOEST KAREN L, BURKHARDT, DENNIS, E., DECIOUS, GAYLON, M., GARBE, JAMES, R., GOTTSCHALK, DONALD, A., JR., HYZER, SUSAN, M., KOCH, DAVID, L., MADAUS, PAUL, W., MAGELAND, OTTO, M., NESLER, CLAY, G., PASCUCCI, GREGORY, A., RASMUSSEN, DAVID, E., SPACEK, DAN, J., STANDISH, DARRELL, E., STARK, JAMES, K., VAIRAVAN, VAIRAVAN, E., WOEST, KAREN, L.
Applicants: JOHNSON SERVICE CO, JOHNSON SERVICE COMPANY
Application year: 1991
Main classification: G06F13
IPC codes: G06F9, G06F11, G06F12, G06F13, G06F15, G06F17, H04L12