Patent Publication Number: US-8527615-B2

Title: Apparatus and method for determining a program neighborhood for a client node in a client-server network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/390,928 filed on Sep. 7, 1999, which is a Continuation-in-part of application Ser. No. 09/252,391 filed on Feb. 18, 1999, now U.S. Pat. No. 6,643,690, which is a non-provisional of U.S. Provisional Patent Application No. 60/114,099 filed on Dec. 29, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     Contemporary computer networks consist of a number of computer systems, called nodes, communicating with other computer systems via communication links. Typically, some of the nodes are client nodes and other nodes are server nodes. A client node formulates and delivers queries to a server node. A user of the client node enters the queries through a user interface operating on the client node. The server node evaluates the queries and delivers responses to the client node for display on the client user interface. 
     Usually, the server nodes host a variety of application programs that can be accessed and executed by client nodes. When a client node launches an application program, the execution of that application program can occur at either the client node or the server node, depending upon the computing model followed by the computer network. In a server-based computing model, the server node executes the application program, and only the control information for the client user interface is transmitted across the computer network to the client node for display. In a client-based computing model, the server node transmits the application program to the client node so that the client node can run the program using the resources of the client node. 
     One drawback of contemporary computer networks is that client nodes may be unaware of the application programs available for use on the server nodes. In fact, client nodes may not even be aware of each available server node on the network. To find available application programs on a particular server node, a user of the client node may need to find and gain access to that server node and perform a directory listing of the files on that server node. Even then, this listing might not indicate to the user those applications which the user is authorized to use. 
     Moreover, once the user is aware of the application programs on a server node, often that user must establish a link to those applications. Industry has developed software tools to aid the user in creating these links, e.g., Remote Application Manager manufactured by Citrix Systems, Inc., of Ft. Lauderdale, Fla. The Remote Application Manager is an application program installed on the client node. This application program guides an administrator of the client node to enter information that establishes a link to an application published on a particular server node. The administrator supplies such information as the name of the session, the protocol for accessing the server node, the server name or IP address or the published application. Approaches of this kind require that the administrator know the information and understand the details of protocols and domains in order to establish the connection. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention enables the user of a client system to become informed about available application programs on servers in a network without requiring the user to know where to find such applications or to enter technical information necessary to link to such applications. 
     In one aspect, the invention relates to a method for presenting application programs to a client system in a network including the client system and a plurality of servers. The servers include a host server that receives application-related information corresponding to application programs hosted by a plurality of servers in a network. User credentials are received from the client system. Whether each hosted application program is available to the client system for execution is determined based on the user credentials and the received application-related information. Information is transmitted from the host server to the client system indicating to the client system each hosted application that is available to the client system for execution. In some embodiments, the host server creates an output display containing the application-related information, such as a HyperText Markup Language (HTML) file, an Extended Markup Language (XML), or other Structured General Markup Language (SGML) file. 
     The host server can authenticate the client system based on received user credentials. When the client system selects one of the available applications for execution, that application can be executed without requiring additional input of user credentials by a user of the client system, although the selected application is at a server other than the host server. 
     In one embodiment, a connection is established between the client system and the host server using an Independent Computing Architecture (ICA) protocol. The ICA protocol can establish a virtual channel to transmit information to the client system indicating each hosted application program that is available to the client system. 
     A request to execute one of the available hosted application programs can be received on the connection. In response to the request, a second connection between the client system and the host server can be established to exchange information associated with an execution of the requested application program. In another embodiment, a connection between the host server and a second server hosting the requested application can be established in response to the request. Information associated with an execution of the requested application program can be exchanged between the second server and the client system via the host server. 
     A second request to execute a second one of the available hosted application programs can be received on the connection between the host server and the client system. Another connection between the host server and a third server hosting the requested application can be established in response to the second request. Information associated with an execution of the second requested application program can be exchanged between the third server and the client system via the host server. Information received from the second and third servers can be merged for transmission to the client system. 
     In still another embodiment, application information can be provided by the host server to the client system in response to the first request. A second connection can be established between the client system and a second server hosting the requested application in response to the provided application information. 
     The host server can transmit the available application information in response to a request by the client system. The transmitted information can produce a graphical user interface display at the client system having icons representing the available application programs. The transmitted information can also disclose each hosted application program that the client system is unauthorized to use. 
     The host server can communicate with each of the other servers to determine the application programs hosted by those other servers and to develop a database for storing the application-related information. The database can be accessible to each of the other servers of the plurality, or each of the other servers can maintain a database for storing the application-related information. 
     In another aspect, the invention relates to a method for presenting to a client system each application hosted by a server that is available to the client system. User credentials are received from the client system. Application-related information is maintained by the server. Whether each application hosted by the server is available to the client system for execution is determined based on the user credentials and the application-related information. Information indicating each application that is available to the client system is transmitted from the server to the client system. 
     In another aspect, the invention relates to a server comprising a service module that collects application-related information corresponding to application programs hosted by the plurality of servers. A database stores the collected application-related information. A receiver receives user credentials from the client system. The service module determines for each application program hosted by the plurality of servers whether that hosted application program is available for use by the user of the client system based on the user credentials and the application-related information stored in the database. A transmitter transmits information to the client system. 
     The service module can transmit a datagram to other servers in the plurality to collect the application-related information corresponding to the application programs hosted by those servers. The transmitted information discloses to a user of the client system each hosted application program that is available for use by the user of the client system. The transmitter can transmit available application information using a virtual channel communications protocol. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is pointed out with particularity in the appended claims. The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram of an embodiment of client nodes in communication with a group of server nodes via a network, wherein a program neighborhood of a client node can be determined according to the principles of the invention; 
         FIG. 2A  is a block diagram illustrating an exemplary process by which one of the server nodes can initiate execution of an application program for determining the program neighborhood of a client node; 
         FIG. 2B  is a block diagram illustrating an exemplary process by which a client node can initiate execution of an application program for determining the program neighborhood of that client node; 
         FIG. 2C  is a block diagram illustrating an exemplary process by which a client node uses a web browser application to determine its program neighborhood; 
         FIGS. 3A ,  3 B, and  3 C are block diagrams illustrating exemplary processes by which a client node can launch an application program from a Program Neighborhood window displayed at that client node; 
         FIG. 3D  is a block diagram illustrating an exemplary process by which a client node can launch an application program from a Program Neighborhood web page displayed at that client node; 
         FIG. 4  is a block diagram of a client-based computing embodiment in which a client node having an installed program neighborhood application of the invention is in communication with one of the server nodes; 
         FIG. 5  is a block diagram of a server-based computing embodiment in which a client node is in communication with a server node having an installed program neighborhood application program of the invention; 
         FIG. 6A  is a screen shot of an exemplary display on the display screen of a client node after the program neighborhood application program of the invention is executed; 
         FIG. 6B  is a screen shot of another exemplary display on the display screen of a client node after the program neighborhood application program of the invention is executed; 
         FIG. 7  is a flow chart representation of an embodiment of a process by which a client node is informed as to the availability for use of application programs on the application servers. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a first computing system (client node)  10  and a second computing system (client node)  20  in communication with computing systems (application servers)  30 ,  32 ,  34 , and  36  over a network  40 . The network  40  can be a local-area network (LAN) or a wide area network (WAN) such as the Internet or the World Wide Web. Users of the client nodes  10 ,  20  can be connected to the network  40  through a variety of connections including standard telephone lines, LAN or WAN links (e.g., T1, T3, 56 kb, X.25), broadband connections (ISDN, Frame Relay, ATM), and wireless connections. The connections can be established using a variety of communication protocols (e.g., TCP/IP, IPX, SPX, NetBIOS, Ethernet, RS232, and direct asynchronous connections). 
     The client node  10  can be any personal computer (e.g., 286, 386, 486, PENTIUM, PENTIUM II, MACINTOSH computer), Windows-based terminal, Network Computer, wireless device, information appliance, RISC Power PC, X-device, workstation, mini computer, main frame computer or other computing device that has a windows-based desktop and sufficient persistent storage for executing application programs downloaded from the application servers  30 ,  32 ,  34  across the network  40 . Windows-oriented platforms supported by the client node  10  can include WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS NT 3.51, WINDOWS NT 4.0, WINDOWS CE, MACINTOSH, JAVA, and UNIX. The client node  10  can include a display screen  12 , a keyboard  14 , memory  16  for storing downloaded application programs, a processor  17 , and a mouse  18 . The memory  16  can provide persistent or volatile storage. The processor  17  can execute the application programs locally on the client node  10  and display a resulting windows-based desktop on the display screen  12 . Such local processing on the client node  10  is according to the above-described client-based computing model. 
     Alternatively, the client node  20  can be any terminal (windows or non-windows based), or thin-client device operating according to a server-based computing model. In a server-based computing model, the execution of application programs occurs entirely on the application servers  30 ,  32 ,  34 , and the user interface, keystrokes, and mouse movements are transmitted over the network  40  to the client node  20 . The user interface can be text driven (e.g., DOS) or graphically driven (e.g., Windows). Platforms that can be supported by the client node  20  include DOS and Windows CE for windows-based terminals. The client node  20  includes a display screen  22 , a keyboard  24 , a mouse  28 , a processor (not shown), and persistent storage (not shown). 
     The application servers  30 ,  32 ,  34 , and  36  can be any computing device that controls access to other portions of the network (e.g., workstations, printers). It is to be understood that more or fewer application servers can be connected to the network  40 . The servers  30 ,  32 ,  34 , and  36  can operate according to either a client-based computing model or a server-based computing model as described above. 
     Each application server  30 ,  32 ,  34 , and  36  hosts one or more application programs that can be accessed by the client nodes  10  and  20 . Applications made available to client nodes for use are referred to as published applications. Examples of such applications include word processing programs such as MICROSOFT WORD® and spreadsheet programs such as MICROSOFT EXCEL®, both manufactured by Microsoft Corporation of Redmond, Wash., financial reporting programs, customer registration programs, programs providing technical support information, customer database applications, or application set managers. 
     The servers  30 ,  32 , and  34  can belong to the same domain  38 . In the network  40 , a domain is a sub-network comprising a group of application servers and client nodes under control of one security database. A domain can include one or more “server farms.” (A server farm is a group of servers that are linked together to act as a single server system to provide centralized administration.) Conversely, a server farm can include one or more domains. For servers of two different domains to belong to the same server farm, a trust relationship may need to exist between the domains. A trust relationship is an association between the different domains that allows a user to access the resources associated with each domain with just one log-on authentication. 
     In one embodiment, the application server  36  is in a different domain than the domain  38 . In another embodiment, the application server  36  is in the same domain as servers  30 ,  32 , and  34 . For either embodiment, application servers  30 ,  32 , and  34  can belong to one server farm, while the server  36  belongs to another server farm, or all of the application servers  30 ,  32 ,  34 , and  36  can belong to the same server farm. When a new server is connected to the network  40 , the new server joins either an existing server farm or starts a new server farm. 
     The network  40  can include a master server node for performing load-level balancing among the application servers  30 ,  32 ,  34 , and  36 . The master server node can be one of the application servers  30 ,  32 ,  34 , or  36 . The master server node includes a list of server addresses and load information corresponding to each of the other application servers. The master server node can direct the client node to a particular server node on which to execute an application based on the list of available servers and corresponding load levels. Alternatively, the application servers  30 ,  32 ,  34 ,  36  may collaborate among themselves in a peer-to-peer fashion in order to exchange administration information such as load levels, allowing any server  30 ,  32 ,  34 ,  36  to respond to a request made by a client node  10 ,  20 . 
     Program Neighborhood 
     According to the principles of the invention, a user of either client node  10 ,  20  is able to learn of the availability of application programs hosted by the application servers  30 ,  32 ,  34 , and  36  in the network  40  without requiring the user to know where to find such applications or to enter technical information necessary to link to such applications. These available application programs comprise the “program neighborhood” of the user. A system for determining a program neighborhood for a client node includes an application program (hereafter referred to as the “Program Neighborhood” application), memory for storing components of the application program, and a processor for executing the application program. 
     The Program Neighborhood application can be installed in memory of the client node  10  and/or on the application servers  30 ,  32 ,  34 , and  36  as described below. The Program Neighborhood application is a collection of services, applications program interfaces (APIs), and user interface (UI) programs that disclose to users of the client nodes  10 ,  20  those application programs hosted by the application servers that each client node is authorized to use (e.g., execute). 
     An application server operating according to the Program Neighborhood application collects application-related information from each of the application servers in a server farm. The application-related information for each hosted application can be a variety of information including, for example, an address of the server hosting that application, the application name, the users or groups of users who are authorized to use that application, and the minimum capabilities required of the client node before establishing a connection to run the application. For example, the application may stream video data, and therefore a required minimum capability is that the client node supports video data. Other examples are that the client node can support audio data or can process encrypted data. The application-related information can be stored in a database as described later in the specification. 
     When a client node logs onto the network  40 , the user of the client node provides user credentials. User credentials typically include the username of the client node, the password of the user, and the domain name for which the user is authorized. The user credentials can be obtained from smart cards, time-based tokens, social security numbers, user passwords, personal identification (PIN) numbers, digital certificates based on symmetric key or elliptic curve cryptography, biometric characteristics of the user, or any other means by which the identification of the user of the client node can be obtained and submitted for authentication. The server responding to the client node can authenticate the user based on the user credentials. The user credentials can be stored wherever the Program Neighborhood application is executing. When the client node  10  executes Program Neighborhood application, the user credentials can be stored at the client node  10 . When an application server is executing the Program Neighborhood, the user credentials can be stored at that server. 
     From the user credentials and the application-related information, the server can also determine which application programs hosted by the application servers are available for use by the user of the client node. The server transmits information representing the available application programs to the client node. This process eliminates the need for a user of the client node to set-up application connections. Also, an administrator of the server can control access to applications among the various client node users. 
     The user authentication performed by the server can suffice to authorize the use of each hosted application program presented to the client node, although such applications may reside at another server. Accordingly, when the client node launches (i.e., initiates execution of) one of the hosted applications, additional input of user credentials by the user may be unnecessary to authenticate use of that application. Thus, a single entry of the user credentials can serve to determine the available applications and to authorize the launching of such applications without an additional, manual log-on authentication process by the client user. 
     Either a client node  10 ,  20  or an application server can launch the Program Neighborhood application as described in connection with  FIGS. 2A-2C . The results are displayed on the display screen  12 ,  22  of the client node  10 ,  20 . In a graphical windows-based implementation, the results can be displayed in a Program Neighborhood graphical window and each authorized application program can be represented by a graphical icon in that window. 
     One embodiment of the Program Neighborhood application filters out application programs that the client node  10 ,  20  is unauthorized to use and displays only authorized (i.e., available) programs. In other embodiments, the Program Neighborhood application can display authorized and unauthorized applications. When unauthorized applications are not filtered from the display, a notice can be provided indicating that such applications are unavailable. Alternatively, the Program Neighborhood application can report all applications hosted by the application servers  30 ,  32 ,  34 ,  36  to the user of a client node, without identifying which applications the client node  10 ,  20  is authorized or unauthorized to execute. Authorization can be subsequently determined when the client node  10 ,  20  attempts to run one of those applications. 
       FIG. 2A  shows an exemplary process by which a server launches the Program Neighborhood (PN) application and presents results of the PN application to the client node  10 . The server can launch the PN application in response to a request  42  by the client node  10  for a particular application program. The request passes to the master server node, in this example server  30 . The master server node  30 , taking load-balancing and application availability into account, indicates (arrow  43 ) to the client node  10  that the sought-after application is available on server  32 . The client node  10  and server  32  establish a connection (arrows  45  and  46 ). By this connection, the server  32  can transfer the executable code of the particular application to the client node  10 , when the client node  10  and server  32  are operating according to the client-based computing model. Alternatively, the server  32  can execute the particular application and transfer the graphical user interface to the client node  10 , when the client node  10  and server  32  are operating according to the server-based computing model. In addition, either the master server node  30  or the server  32  can execute the Program Neighborhood application  41  and push the results (arrows  43  or  46 ) back to the client node  10  so that when the client  5  node  10  requests the Program Neighborhood application, the program neighborhood results are available at the client node  10 . 
       FIG. 2B  shows another exemplary process by which the client node  10  initiates execution of the Program Neighborhood application and a server presents the results of the PN application to the client node  10 . The client node  10  launches the Program Neighborhood application (e.g., by clicking on the Program Neighborhood icon  41  representing the application). The request  50  for the Program Neighborhood application is directed to the master server node, in this example server  30 . The master server node  30  can execute the Program Neighborhood application, if the application is on the master server node  30 , and return the results to the client node  10 . Alternatively, the master server node  30  can indicate (arrow  51 ) to the client node  10  that the Program Neighborhood application  41  is available on another server, in this example server  32 . The client node  10  and server  32  establish a connection (arrows  53  and  54 ) by which the client node  10  requests execution of the Program Neighborhood application  41 . The server  32  can execute the application  41  and transfer the results (i.e., the graphical user interface) to the client node  10 . 
       FIG. 2C  shows another exemplary process by which a client node  20  initiates execution of the Program Neighborhood application, in this example via the World Wide Web. A client node  20  executes a web browser application  80 , such as NETSCAPE NAVIGATOR, manufactured by Netscape Communications, Inc. of Mountain View, Calif. or MICROSOFT INTERNET EXPLORER, manufactured by Microsoft Corporation of Redmond, Wash. 
     The client node  20 , via the web browser  80 , transmits a request  82  to access a Uniform Resource Locator (URL) address corresponding to an HTML page residing on server  30 . In some embodiments the first HTML page returned  84  to the client node  20  by the server  30  is an authentication page that seeks to identify the client node  20 . 
     The authentication page allows the client node  20  to transmit user credentials, via the web browser  80 , to the server  30  for authentication. Transmitted user credentials are verified either by the server  30  or by another server in the farm. This allows a security domain to be projected onto the server  30 . For example, if the server  30  runs the WINDOWS NT operating system, manufactured by Microsoft Corporation of Redmond, Wash., and the authenticating server runs the UNIX operating system, the UNIX security domain may be said to have been projected onto the server  30 . User credentials may be transmitted “in the clear,” or they may be encrypted. For example, user credentials may be transmitted via a Secure Socket Layer (SSL) connection, which encrypts data using the RC3 algorithm, manufactured by RSA Data Security, Inc. of San Mateo, Calif. 
     The server  30  may verify the user credentials received from the client node  20 . Alternatively, the server  30  may pass the user credentials to another server for authentication. In this embodiment, the authenticating server may be in a different domain from the server  30 . Authenticated user credentials of the client node  20  may be stored at the client node  20  in a per-session cookie, in fields that are not displayed by the web browser  80 , or in any other manner common in maintenance of web pages. In some embodiments, a server farm with which the server  30  is associated may allow guest users, i.e., users that do not have assigned user credentials, to access applications hosted by servers in the farm. In these embodiments, the authentication page may provide a mechanism for allowing a client node  20  to identify that it is a guest user, such as a button or menu selection. In other of these embodiments, the server  30  may omit the authentication page entirely. 
     Still referring to  FIG. 2C , once the client node  20  is authenticated by the server  30 , the server prepares and transmits to the client node  20  an HTML page  88  that includes a Program Neighborhood window  58  in which appears graphical icons  57 ,  57 ′ representing application programs to which the client node  20  has access. A user of client node  20  invokes execution of an application represented by icon  57  by clicking that icon  57 . 
       FIG. 3A  shows an exemplary process of communication among the client node  10 , the master server node, in this example server  30 , and the server  32 . The client node  10  has an active connection  72  with the server  32 . The client node  10  and server  32  can use the active connection  72  to exchange information regarding the execution of a first application program. The user credentials of the client node  10  are stored at the client node. Such storage of the user credentials can be in cache memory or persistent storage. 
     In this embodiment, the Program Neighborhood application runs on the client node  10 . The client node display has a Program Neighborhood window  58  in which appears a graphical icon  57  representing a second application program. A user of the client node  10  can launch the second application program by double-clicking the icon  57  with the mouse. The request passes to the master server node  30  via a connection  59 . The master server node  30  indicates to the client node  10  via the connection  59  that the sought-after application is available on server  32 . The client node  10  signals the server  32  to establish a second connection  70 . The server  32  requests the user credentials from the client node  10  to authenticate access to the second application program. Upon a successful authentication, the client node  10  and server  32  establish the second connection  70  and exchange information regarding the execution of the second application program. Accordingly, the client node  10  and the server  32  communicate with each other over multiple connections. 
       FIG. 3B  shows an exemplary process of communication among the client node  20 , the master server node, in this example server  30 , and servers  32 ,  34 , and  36 . The client node  20  has an active connection  73  with the server  32 . The client node  20  and server  32  can use the active connection  73  to exchange information regarding the execution of a first application program. The user credentials of the client node  20  are stored at the server  32  in cache memory or in persistent storage. 
     In this embodiment, the Program Neighborhood application runs on the server  32 . The server  32  includes software providing a server-based client engine  62 , enabling the server  32  to operate in the capacity of the client node  20 . The client node  20  display has a Program Neighborhood window  58  in which appears graphical icons  57 ,  57 ′ representing a second application program and a third application program, respectively. A user of the client node  20  can launch the second application program by double-clicking the icon  57 . The request to launch the second application program passes to the server  32  via active connection  73 , and the server  32  forwards the request to the master server node  30  (arrow  65 ). 
     The master server node  30  indicates (arrow  65 ) to the server  32  that the sought-after application is available on server  34 . The server  32  contacts the server  34  to establish a connection  66 . To authenticate access to the application, the server  34  obtains the user credentials of the client node  20  from the server  32 . The server  32  and server  34  establish the connection (arrow  66 ) by which the server  32  requests execution of the second application and the server  34  returns the graphical user interface results to the server  32 . The server  32  forwards the graphical user interface results to the client node  20 , where the results are displayed. Accordingly, the information exchanged between the client node  20  and the server  34  “passes through” the server  32 . 
     Similarly, the client node  20  can launch the third application program by double-clicking the icon  57 ′. The request to launch the third application program passes to the server  32 . The server  32  forwards the request to the master server node  30 , which considers load-balancing and application program availability to determine which server can handle the request. In this example, the master server node indicates that the server  36  can run the third application program. 
     The server  32  and the server  36  establish a connection (arrow  74 ) by which the server  32  requests execution of the third application program, and the server  36  returns the graphical user interface results to the server  32 . To permit execution of the third application program, the server  36  can authenticate the user credentials of the client node  20 , which are obtained from the server  32 . The server  32  forwards the graphical user interface results to the client node  20  where the results are displayed. Accordingly, the results of executing the third application program pass between the client node  20  and the server  36  through the server  32 . 
     From this illustration it should be understood that client node  20  can run multiple application programs through one connection with the server  32 , while the server  32  maintains multiple connections (in this example, one connection with server  34  and a second connection with server  36 ). Also, the server  32  merges the information received from the server  34  with the information received from the server  36  into one data stream for transmission to the client node  20 . 
       FIG. 3C  shows an exemplary process of communication among the client node  20 , the master server node, in this example server  30 , and servers  32  and  34 . The client node  20  has an active connection  76  with the server  32 . The client node  20  and server  32  can use the active connection  76  to exchange information regarding the execution of a first application program. The client node  20  can store the user credentials in cache memory or in persistent storage. 
     In this embodiment, the Program Neighborhood application runs on the server  32 . The client node  20  display has a Program Neighborhood window  58  in which appears a graphical icon  57  representing a second application program. A user of the client node  20  can launch the second application program by double-clicking the icon  57 . The request to launch the second application program passes to the server  32 . The server  32  responds (i.e., “calls back”) to the client node  20  by returning application-related information such as the name of the application and capabilities needed by the client node  20  for the second application to run. 
     With the information provided by the server  32 , the client node  20  then communicates with the master server node  30  via connection  77  to determine the server for executing the second application program. In this example, that server is server  34 . The client node  20  then establishes a connection  78  to the server  34 . Server  34  requests the user credentials from the client node  20  to authenticate the user of the client node  20 . The second application program executes on the server  34 , and the server  34  returns the graphical user interface to the client node  20  via the established connection  78 . Accordingly, the client node  20  can have multiple active connections between the multiple servers. 
       FIG. 3D  shows an exemplary process of communicating between the client node  20 , a server  30  that in this example acts as a web server, and the server  32 . The client node  20  authenticates itself to the server  30  as described above in connection with  FIG. 2C . In one embodiment, the server  30  accesses an output display template  90 , such as an SGML, HTML or XML file, to use as a base for constructing the Program Neighborhood window to transmit to the client node  20 . The template may be stored in volatile or persistent memory associated with the server  30  or it may be stored in mass memory  92 , such as a disk drive or optical device, as shown in  FIG. 3D . 
     In this embodiment, the template  90  is a standard SGML, HTML, or XML document containing Program Neighborhood-specific tags that are replaced with dynamic information. The tags indicate to the server  30  where in the output display to insert information corresponding to available applications, such as icon images. In one particular embodiment, the Program Neighborhood-specific tags are embedded within comments inside a file, allowing the file to remain compatible with standard interpreters. In another embodiment, the Program Neighborhood-specific tags are extensions of the markup language used as the base for the template. 
     Examples of HTML tags that may be used in a template in accordance with the present invention are set forth below in Table 1: 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Tag 
                 Description 
               
               
                   
               
             
            
               
                 ControlField_/zeW value 
                 This tag is used to set the value of data that  
               
               
                   
                 either persists between Program 
               
               
                   
                 Neighborhood web pages, is set by the user,  
               
               
                   
                 or is used to help in cross page navigation,  
               
               
                   
                 such as user name, domain, password, 
               
               
                   
                 template, and application. 
               
               
                 DrawProgramNeighborhood 
                 This tag is used to draw a Program  
               
               
                   
                 Neighborhood display at this location in 
               
               
                   
                 an output display. 
               
               
                 AppName 
                 This tag is replaced by the name of the  
               
               
                   
                 published application in the current 
               
               
                   
                 context. 
               
               
                 WindowType 
                 This tag is replaced by the window type  
               
               
                   
                 of the published application in the 
               
               
                   
                 current context. 
               
               
                 WindowHeight 
                 This tag is replaced by the window height  
               
               
                   
                 of the published application in the 
               
               
                   
                 current context. 
               
               
                 WindowWidth 
                 This tag is replaced by the window width  
               
               
                   
                 of the published application in the 
               
               
                   
                 current context. 
               
               
                 WindowScale 
                 This tag is replaced by the window scale 
               
               
                   
                 of the published application in the 
               
               
                   
                 current context. 
               
               
                 WindowColors 
                 This tag is replaced by the color depth of  
               
               
                   
                 the published application in the 
               
               
                   
                 current context. 
               
               
                 SoundType 
                 This tag is replaced by the sound setting of  
               
               
                   
                 the published application in the 
               
               
                   
                 current context. 
               
               
                 VideoType 
                 This tag is replaced by the video setting of  
               
               
                   
                 the published application in the 
               
               
                   
                 current context. 
               
               
                 EncryptionLevel 
                 This tag is replaced by the encryption level  
               
               
                   
                 of the published application in the 
               
               
                   
                 current context. 
               
               
                 Icon 
                 This tag is replaced by the icon of the  
               
               
                   
                 published application in the 
               
               
                   
                 current context. 
               
               
                   
               
            
           
         
       
     
     Other tags can be provided to set control fields and to provide conditional processing relating to the Program Neighborhood application. 
     In one embodiment, the template is constructed dynamically using, for example, COLD FUSION, manufactured by Allaire Corp. of Cambridge, Mass. or ACTIVE SERVER SERVER PAGES manufactured by Microsoft Corporation of Redmond, Wash. Alternatively, the template may be static. The Program neighborhood application parses the template, replacing Program Neighborhood-specific tags as noted above. Tags that are not Program Neighborhood-specific are left in the file to be parsed by the browser program  80  executing on the client  20 . 
     In one embodiment, a template parser object is provided that accepts an HTML template as input, interprets Program Neighborhood-specific tags present in the template, and outputs the original template with all Program Neighborhood tags replaced with appropriate text. The template parser object can be passed a cookie, a URL query string, or a control field from a web server interface to provide the information with which Program Neighborhood-specific tags should be replaced. 
     In another embodiment, the Program Neighborhood application allows scripts to access to information via an application programming interface. Scripts may be written in, for example, VBScript or Jscript. In this embodiment, the scripting language is used to dynamically generate an output display using information returned by the application in response to queries posed by the script. Once the output display is generated, it is transmitted to client node  20  for display by the browser program  80 . 
     A user of the client node  20  can launch an application by double-clicking with a mouse an icon  57 ,  57 ′ displayed in the Program Neighborhood web page. In some embodiments, each icon  57 ,  57 ′ is an encoded URL that specifies: the location of the application (i.e., on which servers it is hosted or, alternatively, the address of a master server); a launch command associated with the application; and a template identifying how the output of the application should be displayed (i.e., in a window “embedded” in the browser or in a separate window). In some embodiments, the URL includes a file, or a reference to a file, that contains the information necessary for the client to create a connection to the server hosting the application. This file may be created by the Program Neighborhood application dynamically. The client node  20  establishes a connection (arrow  94 ) with the server identified as hosting the requested application (in this example, server  32 ) and exchanges information regarding execution of the desired application. In some embodiments, the connection  94  is made using the Independent Computing Architecture (ICA) protocol, manufactured by Citrix Systems, Inc. of Fort Lauderdale, Fla. Thus, the client node  20  may display application output in a window separate from the web browser  80 , or it may “embed” application output within the web browser.  FIG. 4  illustrates an exemplary arrangement of program components for a client-based implementation of the Program Neighborhood application. A client-based implementation of Program Neighborhood application can be used in a network using either the server-based computing model in which the servers execute the Program Neighborhood application or the client-based computing model in which the client node  10  executes the Program Neighborhood application locally. The Program Neighborhood application includes a Program Neighborhood Service (PNSVC) component  44 , an Application Database component  48 , a Program Neighborhood Application Program Interface (PNAPI) component  52 , a Program Neighborhood User Interface component  56 , and a local cache  60 . 
     The application server  30 , for example, includes the service component (PNSVC)  44  and the application database  48 . The client node  10 , which is a representative example of a client node that can support a client-based implementation of the Program Neighborhood application, includes the application program interface PNAPI  52 , the user interface user interface component  56 , and the local cache  60  components. The PNAPI  52  communicates with the user interface component  56  and the local cache  60 . The PNSVC  44  communicates with the application database  48  and with the PNAPI  52  on the client node  10  via communications link  62 . 
     The communications link  62  can be established by, for example, using the ICA protocol. ICA is a general-purpose presentation services protocol designed to run over industry standard network protocols, such as TCP/IP, IPX/SPX, NetBEUI, using industry-standard transport protocols, such as ISDN, frame relay, and asynchronous transfer mode (ATM). The ICA protocol provides for virtual channels, which are session-oriented transmission connections that can be used by application-layer code to issue commands for exchanging data. The virtual channel commands are designed to be closely integrated with the functions of client nodes. One type of virtual channel connection supported by the ICA protocol is a Program Neighborhood virtual channel. The Program Neighborhood virtual channel protocol can include four groups of commands:
         (1) initialization-related commands;   (2) single authentication related commands that can be supported by each client node wanting a copy of the user credentials;   (3) application data related commands for implementing the Program Neighborhood user interface; and   (4) application launch callback-related commands for running the user interface on an application server.       

     Application Database 
     The application database  48  is a cache of the authorized user and group information for all the public (i.e., published) applications in a server farm or in a group of trusted domains. Each server in a server farm can maintain its own application-related information in persistent storage and build up the database  48  in volatile storage. In another embodiment, all collected application-related information in the database  48  can be stored in persistent storage and made accessible to each other server in the server farm. The database  48  can be implemented in a proprietary format (e.g., as a linked list in 15 memory) or using Novell&#39;s Directory Services (NDS) or any directory service adhering to the X.500 standard defined by the International Telecommunication Union (ITU) for distributed electronic directories. 
     The application database  48  includes a list of application servers. Each server in the list has an associated set of applications. Associated with each application is 20 application-related information that can include the application name, a list of servers, and client users that are authorized to use that application. An overly-simplified example of the application-related information maintained in the database is illustrated by the following Table 2. Users A and B are users of the client nodes  10 ,  20 , “n/a” indicates that the application is hosted, but is not available to client node users, and “-” indicates that the application is not hosted. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Applications 
               
            
           
           
               
               
               
               
               
            
               
                 Server 
                   
                 Customer 
                 Word 
                   
               
               
                 Name 
                 Spreadsheet 
                 Database 
                 Processor 
                 Calculator 
               
               
                   
               
               
                 Server 30 
                 User A 
                 User B 
                 n/a 
                 — 
               
               
                 Server 32 
                 User B 
                 n/a 
                 User A 
                 — 
               
               
                 Server 34 
                   
                   
                   
                 User A 
               
               
                   
                   
                   
                   
                 User B 
               
               
                   
               
            
           
         
       
     
     Table 2 shows a list of servers  30 ,  32 ,  34 , the applications hosted by the servers, (Spreadsheet, Customer Database, Word Processor, and Calculator), and those users who are authorized to use the applications. For example, the server  30  hosts the Spreadsheet program, the Customer Database and the Word Processor. User A is authorized to use the Spreadsheet, User B is authorized to use the Customer Database, and no users are authorized to use the Word Processor. It is to be understood that other techniques can be used to indicate who is authorized to use a particular application. For example, the user information stored in the database can be used to indicate those users who are unauthorized to use a particular application rather than those who are authorized. 
     To obtain the information that is stored in the database  48 , the server  30  obtains the application-related information from each other server in the server farm regarding the applications on those servers, including control information that indicates which client users and servers are permitted to access each particular application. The application-related information maintained in the database may or may not persist across re-boots of the server  30 . 
     The application database  48  can be a central database that is stored at the application servers  30 ,  32 , and  34  and are accessible to all of the servers in the server farm. Accordingly, the application-related information can be available for use by other servers such as those servers that perform published application authentication during session log-on and application launching. In another embodiment, the application database  48  can be maintained at each of the application servers  30 ,  32 , and  34  based upon the information that each server obtains from communications with each other server in the server farm. 
     Program Neighborhood Service Program (PNSVC) 
     Each server  30 ,  32 ,  34  and  36  having the Program Neighborhood application installed thereon executes the PNSVC software  44 . The PNSVC software  44 , operating on each server  30 ,  32 ,  34  and  36  establishes a communication link (e.g., a named pipe) with each other server. The servers  30 ,  32 ,  34  and  36  exchange the application-related information on the named pipes. In another embodiment, the PNSVC software  44  collects the application-related information from the other servers in the server farm through remote registry calls (e.g., the service component  44  transmits a datagram to other servers in the plurality requesting the application-related information corresponding to the application programs hosted by those servers). The PNSVC  44  software also maintains the relationships of groups and users to published applications in the application database  48  and accesses the information when authenticating a client user. An administrator of the server  30  can use a user interface to configure the PNSVC  44 . 
     Other functions of the PNSVC software  44  include implementing the services and functions requested by the PNAPI  52  and communicating with the PNAPI  52  on the client node  10  using a Program Neighborhood virtual device driver (VDPN). The VDPN operates according to the Program Neighborhood virtual channel protocol described above for establishing and maintaining an ICA connection. 
     Program Neighborhood Application Program Interface (PNAPI) 
     The PNAPI  52  is a set of software functions or services that are used by the Program Neighborhood application to perform various operations (e.g., open windows on a display screen, open files, and display message boxes). The PNAPI  52  provides a generic mechanism for launching application objects (e.g., icons) produced by running the Program Neighborhood application and application objects in a legacy (i.e., predecessor or existing for some time) client user interface. When the client node  10  launches an available application, the launch mechanism can launch the application on the server  30 , if necessary (e.g., when the client node  10  does not have the resources to locally execute the application). 
     The PNAPI  52  provides all published application information to the user interface component  56  for display on the screen  12  ( FIG. 1 ) of the client node  10 . The PNAPI  52  also manages server farm log-ons in a local database of logon credentials (e.g., passwords) for users of the client node  10  to support the single authentication feature. Credentials may or may not be persistent across bootings (power-off and on cycles) of the client node  10 . 
     The PNAPI  52  provides automatic and manual management for Program Neighborhood application objects stored in the local cache  60 . The local cache  60  can either be refreshed manually by the user of the client node  10 , or at a user-definable refresh rate, or by the server at any time during a connection. In a WINDOWS implementation, the PNAPI  52  can build remote application file associations and manage the “Start” menu and desktop icons for application object shortcuts. 
     Program Neighborhood User Interface 
     The user interface module  56  interfaces the PNAPI  52  and can be a functional superset of an existing client-user interface (e.g., Remote Application Manager). The user interface module  56  accesses the information stored in the local cache  60  through the PNAPI  52  and visually presents that information to the user on the display screen  12  ( FIG. 1 ) of the client node  10 . The displayed information is a mixture of information generated by a user of the client node  10  and information obtained by the Program Neighborhood application. The user interface module  56  can also show the user all applications that the user is currently running and all active and disconnected sessions. 
     In a windows-based embodiment, the user interface module  56  can present a variety of graphical components, such as windows and pull-down menus, to be displayed on the display screen  12  ( FIG. 1 ). A display of a combination of such graphical user interface components is generally referred to as a “desktop.” A desktop produced by the user interface module  56  can include a Program Neighborhood window displaying the neighborhood of application programs available to the user of the client node  10  for use. These application programs are a filtered combination of the published applications hosted by a server farm on the network. The user interface module  56  can generate a Program Neighborhood window for each server farm or merge the applications from different server farms under a single Program Neighborhood window. 
     At a top level, the Program Neighborhood window includes a folder for each server farm. Clicking on one of the folders with the mouse  18  ( FIG. 1 ) produces a window containing a representation (e.g., an icon) of each hosted application available to the user, e.g., see  FIGS. 6A and 6B . The Program Neighborhood window becomes the focal point for launching published applications, and the user interface module  56  can be used to launch applications through the PNAPI  52 . For example, the user of the client node  10  can use the mouse  18  to select one of the displayed icons and launch the associated application. 
     A feature of a client-based implementation is that the user can browse the objects displayed in the Program Neighborhood window although the client node is offline, that is, the ICA connection  62  is inactive. Also, a user of the client node  10  can drag application objects and folders out of the Program Neighborhood window and into other graphical components (e.g., other windows, folders, etc.) of the desktop. 
       FIG. 5  shows an exemplary arrangement of program components for a server-based implementation of the Program Neighborhood application. The components include a Service (PNSVC) component  44 ′, an Application Database component  48 ′, an Application Program Interface (PNAPI) component  52 ′, a User Interface component  56 ′ and a local cache  60 ′. Each software component  44 ′,  48 ′,  52 ′,  56 ′, and  60 ′ is installed on the application server  30 ′. The software components for the server-based implementation correspond to the software components for the client-based implementation of  FIG. 4 . The functionality of each server-based software component is similar to the client-based counterpart, with differences or added capabilities described below. The PNSVC  44 ′ communicates with the application database  48 ′ and with the PNAPI  52 ′ using local procedure calls. The PNAPI  52 ′ also communicates with the user interface module  56 ′ and the local cache  60 ′. 
     Similar to that described in  FIG. 4  for the client node  10 , the client node  20  logs on to the network  40  ( FIG. 1 ), the server  30 ′ develops and maintains a database containing the application related information collected from the other servers  32 ,  34  in the server farm, and a communication link is established between the server  30 ′ and the client node  20 . The application server  30 ′ is in communication with the client node  20  via an ICA channel connection  62 ′. The channel connection  62 ′ can be established by an ICA virtual channel protocol (e.g., Thinwire). The Thinwire protocol can be used to transmit presentation commands from Windows-based applications running on the application server  30 ′ to the client node  20 . To a user of the client node  20 , the applications appear to be running on the client node  20 . The client node  20  can include a Remote Application Manager application program  64  that communicates with the application server  30 ′ via the ICA channel connection  62 ′. 
     To run the Program Neighborhood application in a server-based implementation, the user of the client node  20  connects to an initial desktop (at the server  30 ′) and launches the Program Neighborhood application from within that desktop environment. The connection to the initial desktop can occur automatically, e.g., via a logon script of the client node  20 , via an entry in the StartUp group in WINDOWS 95, or by another centrally managed server specific mechanism. All remote application management and launching is accomplished through this initial desktop. 
     Similar to that described in  FIG. 4  for the server  30 , the server  30 ′ uses the user credentials to determine those application programs that are authorized for use by the user of the client node  20 . A Program Neighborhood graphical window is returned to the client node  20  and displayed on the client screen  22  ( FIG. 1 ). This window can contain icons representing the available and, possibly, the unavailable application programs that are in the program neighborhood of the client node  20 . 
     The user of the client node  20  can select and launch one of the application programs displayed in the Program Neighborhood window. When launching an application, the Program Neighborhood application can execute the application on the same server  30 ′, where applicable, taking into account load balancing requirements among servers and the availability of the application on that server  30 ′. The PNAPI  52 ′ can include a launch mechanism for launching a remote application locally on the server  30 ′ when the server  30 ′ is nominated to launch the application. When a different server is needed to run the application, the Program Neighborhood application can launch the application via the server  30 ′ (i.e., server-based client) using the windows to present the application on the desktop of the client node  20  as described above in  FIG. 3B . 
     In one embodiment, the web-based Program Neighborhood application includes a group of objects that manage various aspects of the application. In one embodiment, the application includes three primary object classes that “plug in” to a web server: a gateway object class; a credentials object class; and an applications object class. In some specific embodiments, the object classes are provided as JAVA BEANS. The three primary object classes facilitate: validation of user credentials into a server farm; generation of lists of published applications that a specified user may access; provision of detailed information about a specific published application; and conversion of published application information into an ICA-compatible format. 
     When provided as JAVA BEANS, the objects can be accessed in a number of different ways. For example, they may be compiled as COM objects and made available to the web server as ACTIVEX components. In another embodiment, the JAVA BEANS can be used in their native form, such as when the server uses JAVA Server Pages technology. In yet another embodiment, the JAVA BEANS can be instantiated and used directly in a JAVA servlet. In still another embodiment, the server  30  can instantiate the JAVA BEANS as COM objects directly. 
     A credentials object class manages information necessary to authenticate a user into a target server farm. A credentials object passes stored user credentials to other Program Neighborhood objects. In some embodiments, the credentials object is an abstract class that cannot be instantiated and represents a user&#39;s credentials. Various class extensions may be provided to allow different authentication mechanisms to be used, including biometrics, smart cards, token-based authentication mechanisms such as challenge-response and time-based password generation, or others. For example, a “clear text credentials” extension may be provided that stores a user&#39;s name, domain, and password in plain text. 
     A gateway object class handles communications with a target server farm. In one embodiment, the gateway object class is provided as an abstract JAVA class that cannot be instantiated. A particular gateway object may retrieve application information by communicating with a server farm using a particular protocol, reading cached application information, a combination of these two methods, or other various methods. 
     As noted above, the gateway object class caches information to minimize communication with a target server farm. Extensions to the gateway object may be provided to communicate with the server farm over specific protocols, such as HTTP. In one embodiment, an extension class is provided that allows the gateway object to communicate with the server farm via WINDOWS NT named pipes. The gateway object may provide an application programming interface hook that allows other Program Neighborhood objects to query the object for application information. 
     An applications object class contains information about published applications and returns information about applications hosted by the server farm in order to create the Program Neighborhood web page. The applications object class creates objects representing applications by retrieving information relating to the applications, either from an object created by the gateway object or directly from the servers in the server farm. An applications object acts as a container for certain properties of the application, some settable and some not settable, such as: the name of the application (not settable); the percentage of the client&#39;s desktop that the client window should occupy (settable); the width of the client window, in pixels, for this application (settable); the height off the client window, in pixels, for this application (settable); the number of colors to use when connecting to the application (settable); the severity of audio bandwidth restriction (settable); the level of encryption to use when connecting to the application (settable); the level of video to use when connecting to this application (settable); whether the application should be placed on a client&#39;s start menu (settable); whether the application should be placed on the client&#39;s desktop (settable); the identity of the Program Neighborhood folder to which the application belongs (settable); the description of the application (settable); the source of the graphics icon file for the application (settable); the type of window that should be used when connecting to the application (not settable); and whether to override default parameters for the object. 
       FIG. 6A  is a screenshot of an exemplary Program Neighborhood window  120  that can be displayed on the screen  18 ,  22  ( FIG. 1 ) of either client node  10 ,  20  after the Program Neighborhood application has executed. The window  120  includes graphical icons  122 . Each icon  122  represents an application program that is hosted by one of the servers  30 ,  32 ,  34  and  36  on the network  40  ( FIG. 1 ). Each represented application is available to the user of the client node for execution. The user can select and launch one of the applications using the mouse  18 ,  28  or keyboard  14 ,  24 . 
       FIG. 6B  is a screenshot of another exemplary Program Neighborhood window  124  that can be displayed on the screen  12 ,  22  ( FIG. 1 ) of either client node  10 ,  20  after the Program Neighborhood application has executed. The window  124  includes graphical icons  126 ,  128 . Each icon  126 ,  128  represents an application program that is hosted by one of the servers  30 ,  32 ,  34  and  36  on the network  40  ( FIG. 1 ). Each application program represented by one of the icons  126  is available to the user of the client node  10 ,  20  for execution. The user can select and launch one of the applications using the mouse  18 ,  28  or keyboard  14 ,  24 . For web-based program neighborhood environments, the screenshots of  FIGS. 6A and 6B  are similar, except that icons  122 ,  166 ,  128  are displayed within a browser window. 
     Each application program represented by one of the icons  128  is unavailable to the user of the client node  10 ,  20  ( FIG. 1 ), although such applications are present in the server farm. The unavailability of these application programs can be noted on the display screen (e.g., “X”s can be drawn through the icons  128 ). An attempt to launch such an application program can trigger a message indicating that the user is not authorized to use the application. 
       FIG. 7  shows an exemplary process by which a user of either client node  10 ,  20  can be informed about the availability of applications hosted by application servers  30 ,  32 ,  34  and  36  on the network  40  ( FIG. 1 ). In step  80 , the client node  10 ,  20  requests log-on service from one of the servers, e.g., server  32 . The server  32  requires valid user credentials to establish the connection. The server  32  receives the user credentials from the client node  10  (step  82 ), and authenticates the user for log-on (step  84 ). A desktop is displayed at the client node  10 ,  20  (step  85 ). The desktop can include a graphical icon representing the Program Neighborhood application program. 
     In step  86 , the application server  32  establishes a connection with each other servers  30 ,  34  and  36  to exchange application-related information, as described above, corresponding to application programs hosted on those servers (step  88 ). In step  90 , the application server  32  develops and maintains a database of the collected application-related information. Each other server  30 ,  34 ,  36  in the server farm can develop a database equivalent to the database of the server  32  and in similar manner as the server  32 . In another embodiment, the database of the server  32  can be a centralized database that is accessible to each other application server  30 ,  34 ,  36  in the server farm. The collecting of application-related information can occur independently or be triggered by the request of the client node  10 ,  20  to log-on to the server farm  38 . 
     In step  92 , the client node  10 ,  20  can request execution of an application program from the desktop display. The master server node can process the request and, using a load-balancing evaluation and application availability as described above, determine the application server to provide the service to the client node  10 ,  20  (step  94 ). For example, the application server  32  can be selected to service the request with the client node  10 ,  20 . In step  96 , the client node  10 ,  20  establishes a communications link with the server  32 . The server  32  and the client node  10 ,  20  can communicate according to the ICA protocol appropriate for that client node as described above. 
     Also in response to this request to run the application program, the master server node  30  or the server  32  can run the Program Neighborhood application (step  93 ) and push the results to the client node  10 ,  20 , although the client node  10 ,  20  may not have requested the PN application program. When executing the PN application program, the master server node  30  or server  32  filters the application-related information in the database using the user credentials (step  100 ). The result of filtering the database determines those application programs that are authorized for use by the user of the client node  10 ,  20 . The authorized application programs are in the program neighborhood of the client node  10 ,  20 . This program neighborhood of available application information is pushed to the client node  10 ,  20  (step  102 ) and displayed on the client screen  12 ,  22  in a Program Neighborhood graphical window (step  104 ). 
     In other embodiments, the Program Neighborhood window may include applications that are in the server farm but unavailable for use to the client node  10 ,  20 . In a Windows-based implementation, the available (and unavailable) application programs can be represented by icons. The user of the client node  10 ,  20  can select and launch one of the application programs displayed in the Program Neighborhood window. 
     The present invention may be provided as one or more computer-readable programs embodied on or in one or more articles of manufacture. The article of manufacture may be a floppy disk, a hard disk, a CD ROM, a flash memory card, a PROM, a RAM, a ROM, or a magnetic tape. In general, the computer-readable programs may be implemented in any programming language. Some examples of languages that can be used include C, C++, or JAVA. The software programs may be stored on or in one or more articles of manufacture as object code. 
     While the invention has been shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the following claims.