Patent Publication Number: US-6708171-B1

Title: Network proxy

Description:
RELATED APPLICATIONS 
     This application is a Continuation-In-Part of U.S. patent application Ser. No. 09/044,826, filed on Mar. 20, 1998, which is a Continuation-In-Part of U.S. Pat. application Ser. No. 08/636,706 filed Apr. 23, 1996 now abandoned, which are both incorporated herein by reference. 
     The following applications are relied upon and are hereby incorporated by reference in this application. 
     Provisional U.S. Patent Application No. 60/076,048, entitled “Distributed Computing System,” filed on Feb. 26, 1998. 
     U.S. patent application Ser. No. 09/044,923, entitled “Method and System for Leasing Storage,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,263,350. 
     U.S. patent application Ser. No. 09/044,838, entitled “Method, Apparatus, and Product for Leasing of Delegation Certificates in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,247,026. 
     U.S. patent application Ser. No. 09/044,834, entitled “Method, Apparatus and Product for Leasing of Group Membership in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,421,704. 
     U.S. patent application Ser. No. 09/044,916, entitled “Leasing for Failure Detection,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,016,500. 
     U.S. patent application Ser. No. 09/044,933, entitled “Method for Transporting Behavior in Event Based System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,463,446. 
     U.S. patent application Ser. No. 09/044,919, entitled “Deferred Reconstruction of Objects and Remote Loading for Event Notification in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,272,559. 
     U.S. patent application Ser. No. 09/044,938, entitled “Methods and Apparatus for Remote Method Invocation,” filed on March 20, 1998 now U.S. Pat. No. 6,487,607. 
     U.S. patent application Ser. No. 09/045,652, entitled “Method and System for Deterministic Hashes to Identify Remote Methods,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,134,603. 
     U.S. patent application Ser. No. 09/044,790, entitled “Method and Apparatus for Determining Status of Remote Objects in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,598,094. 
     U.S. patent application Ser. No. 09/044,930, entitled “Downloadable Smart Proxies for Performing Processing Associated with a Remote Procedure Call in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,393,497. 
     U.S. patent application Ser. No. 09/044,917, entitled “Suspension and Continuation of Remote Methods,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,237,024. 
     U.S. patent application Ser. No. 09/044,835, entitled “Method and System for Multi-Entry and Multi-Template Matching in a Database,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,182,083. 
     U.S. patent application Ser. No. 09/044,839, entitled “Method and System for In-Place Modifications in a Database,” filed on Mar. 20, 1998 now abandoned. 
     U.S. patent application Ser. No. 09/044,945, entitled “Method and System for Typesafe Attribute Matching in a Database,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,578,044. 
     U.S. patent application Ser. No. 09/044,931, entitled “Dynamic Lookup Service in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,185,611. 
     U.S. patent application Ser. No. 09/044,939, entitled “Apparatus and Method for Providing Downloadable Code for Use in Communicating with a Device in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,560,656. 
     U.S. patent application Ser. No. 09/044,932, entitled “Apparatus and Method for Dynamically Verifying Information in a Distributed System,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,466,947. 
     U.S. patent application Ser. No. 09/030,840, entitled “Method and Apparatus for Dynamic Distributed Computing Over a Network,” filed on Feb. 26, 1998 now U.S. Pat. No. 6,446,070. 
     U.S. patent application Ser. No. 09/044,936, entitled “An Interactive Design Tool for Persistent Shared Memory Spaces,” filed on Mar. 20, 1998 now abandoned. 
     U.S. patent application Ser. No. 09/044,934, entitled “Polymorphic Token-Based Control,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,438,614. 
     U.S. patent application Ser. No. 09/044,915, entitled “Stack-Based Access Control,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,138,238. 
     U.S. patent application Ser. No. 09/044,944, entitled “Stack-Based Security Requirements,” filed on Mar. 20, 1998 now U.S. Pat. No. 6,226,746. 
     U.S. patent application Ser. No. 09/044,837, entitled “Per-Method Designation of Security Requirements,” filed on Mar. 20, 1998 U.S. Pat. No. 6,282,652. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to data processing systems and, more particularly, to a network proxy. 
     BACKGROUND OF THE INVENTION 
     In modern “enterprise” computing, a number of personal computers, workstations, and other devices such as mass storage subsystems, network printers and interfaces to the public telephony system, are typically interconnected in one or more computer networks. The personal computers and workstations are used by individual users to perform processing in connection with data and programs that may be stored in the network mass storage subsystems. In such an arrangement, the personal computers/workstations, operating as clients, typically download the data and programs from the network mass storage subsystems for processing. In addition, the personal computers or workstations will enable processed data to be uploaded to the network mass storage subsystems for storage, to a network printer for printing, to the telephony interface for transmission over the public telephony system, or the like. In such an arrangement, the network mass storage subsystems, network printers and telephony interface operate as servers, since they are available to service requests from all of the clients in the network. By organizing the network in such a manner, the servers are readily available for use by all of the personal computers/workstations in the network. Such a network may be spread over a fairly wide area, with the personal computers/workstations being interconnected by communication links such as electrical wires or optic fibers. 
     In addition to downloading information from servers for processing, a client, while processing a program, can remotely initiate processing by a server computer of particular routines and procedures (generally “procedures”), in connection with certain “parameter” information provided by the client. After the server has processed the procedure, it will provide results of its processing to the client, which the client may thereafter use in its processing operations. Typically in such “remote procedure calls” the program will make use of a local “stub” which, when called, transfers the request to the server which implements the particular procedure, receives the results and provides them to the program. Conventionally, the stub must be compiled with the program, in which case the information needed to call the remote procedure must be determined at compile time, rather than at the time the program is run. Since the stub available to the client&#39;s programs is static, it may be at best the closest that can be determined should be provided for the program when it (the program) is compiled. Accordingly, errors and inefficiencies can develop due to mismatches between the stub that is provided to a program and the requirements of the remote procedure that is called when the program is run. 
     SUMMARY OF THE INVENTION 
     A new and improved system and method for facilitating the obtaining and dynamic loading of a stub is provided to enable a program operating in one address space to remotely invoke processing of a method or procedure in another address space, so that the stub can be loaded by the program when it is run and needed, rather than being statically determined when the program is compiled. Indeed, the stub that is loaded can be obtained from the resource providing the remote method or procedure, and so it (the stub) can exactly define the invocation requirements of the remote method or procedure. Since the stub can be located and dynamically loaded while the program is being run, rather than being statically determined when the program is compiled, run-time errors and inefficiencies which may result from mismatches between the stub that is provided and the requirements of the remote method or procedure that is invoked can be minimized. In an alternative embodiment of the present invention, the stub is obtained from a lookup service to provide access to a service defined in the lookup service. 
     In brief summary, methods and systems consistent with an alternative embodiment of the present invention facilitate access to a service via a lookup service. A lookup service defines a network&#39;s directory of services and stores references to these services. A client desiring use of a service on the network accesses the lookup service, which returns the stub information that facilitates the user&#39;s access of the service. The client uses the stub information to access the service. 
     In a second alternative embodiment of the present invention, a network proxy is provided that facilitates the integration of orphan services into a network by enabling them to interact with a lookup service that contains an indication of the services that are available on the network. In this respect, the lookup service acts like a service registry. These orphan services typically reside on devices having too little memory to run the components necessary to be integrated into the network. Thus, the network proxy acts as a go between, by registering the orphan services with the lookup service so that clients may access them and by accessing services on behalf of the orphan services. As a result, the network proxy integrates orphan services into the network when they otherwise would be incapable of doing so. 
     In accordance with methods consistent with the present invention, a method is provided in a data processing system including a service on a device, a service registry, and a proxy. According to this method, the proxy receives a request from the service to register with the service registry, obtains information that facilitates accessing the service, and stores the information into the service registry. 
     In accordance with methods consistent with the present invention, a method for registering a service located on a device in a service registry is provided in a data processing system. According to this method, the service sends a request for registration in the service registry to a proxy server, whereupon the proxy server registers the service in the service registry to enable a client program to access the service, and the service receives a request from the client program for accessing the service. 
     In accordance with methods consistent with the present invention, a method is provided in a data processing system including a client program, a service registry containing a reference to a service on a device, and a proxy server. According to this method, the client program retrieves the reference from the service registry and uses the reference to send a request to access the service to the proxy server. 
     In accordance with systems consistent with the present invention, a data processing system is provided. The data processing system comprises a lookup server, a device, and a proxy server. The lookup server includes a memory with a lookup service containing registrations that facilitate access to corresponding services and includes a processor for running the lookup service. The device includes a memory containing an orphan service that requests registration in the lookup service and includes a processor for running the orphan service. The proxy server includes a memory containing a network proxy that receives the registration request from the orphan service and that registers the orphan service in the lookup service and includes a processor for running the network proxy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention is pointed out with particularity in the appended claims. The above and further advantages of this invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a function block diagram of a computer network including an arrangement constructed in accordance with the present invention for facilitating the obtaining, dynamic loading and use of “stub” information to enable a program operating in one address space to invoke processing of a remote method or procedure in another address space; 
     FIGS. 2 and 3 are flow charts depicting the operations performed by the arrangement depicted in FIG. 1, with FIG. 2 depicting operations performed in connection with obtaining and dynamic loading of the stub information and FIG. 3 depicting operations performed in connection with use of the stub information to invoke processing of the remote method or procedure; 
     FIG. 4 is a diagram illustrating a lookup service consistent with the present invention; 
     FIG. 5 is a flowchart illustrating a method of adding a stub to the lookup service consistent with the present invention; 
     FIG. 6 is a flowchart illustrating a method for retrieving a stub from a lookup service by systems consistent with the present invention; 
     FIG. 7 depicts a data processing system suitable for use with a second alternative embodiment of the present invention; 
     FIG. 8 depicts a flowchart of the steps performed when the network proxy depicted in FIG. 7 registers an orphan service with the lookup service depicted in FIG. 7 in accordance with methods and systems consistent with the present invention; 
     FIG. 9 depicts a flowchart of the steps performed when the network proxy depicted in FIG. 7 registers an orphan service with the lookup service depicted in FIG. 7 in accordance with an alternative embodiment of the present invention; and 
     FIG. 10 depicts a flowchart of the steps performed when the network proxy depicted in FIG. 7 manages resource allocation on behalf of the orphan service. 
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
     FIG. 1 is a schematic diagram of a computer network  10  including an arrangement for facilitating dynamic loading of “stub” information to enable a program operating in one address space to remotely invoke processing of a method or procedure in another address space, where this method or procedure represents a network service. With reference to FIG. 1, computer network  10  includes a plurality of client computers  11 ( 1 ) through  11 (N) (generally identified by reference numeral  11 ( n )), a plurality of server computers  12 ( 1 ) through  12 (M) (generally identified by reference numeral  12 ( m )), all of which are interconnected by a network represented by a communication link  14 . In addition, the network  10  may include at least one nameserver computer  13 , which may also be connected to communication link  14 , whose purpose will be described below. As is conventional, at least some of the client computers  11 ( n ) are in the form of personal computers or computer workstations, each of which typically includes a system unit, a video display unit and operator input devices such as a keyboard and mouse (all of which are not separately shown). The server computers  12 ( m ) and nameserver computer  13  also typically include a system unit (also not separately shown), and may also include a video display unit and operator input devices. 
     The client computers  11 ( n ), server computers  12 ( m ) and nameserver computer  13  are all of the conventional stored-program computer architecture. A system unit generally includes processing, memory, mass storage devices such as disk and/or tape storage elements and other elements (not separately shown), including network interface devices  15 ( n ),  16 ( m ) for interfacing the respective computer to the communication link  14 . The video display unit permits the computer to display processed data and processing status to the operator, and an operator input device enables the operator to input data and control processing by the computer. The computers  11 ( n ) and  12 ( m ) and  13  transfer information, in the form of messages, through their respective network interface devices  15 ( n ),  16 ( m ) among each other over the communication link  14 . 
     In one embodiment, the network  10  is organized in a “client-server” configuration, in which one or more computers, shown in FIG. 1 as computers  12 ( m ), operate as servers, and the other computers, shown in FIG. 1 as computers  11 ( n ) operate as clients. In one aspect, one or more of the server computers  12 ( m ) may, as “file servers,” include large-capacity mass storage devices which can store copies of programs and data which are available for retrieval by the client computers over the communication link  13  for use in their processing operations. From time to time, a client computer  11 ( n ) may also store data on the server computer  12 , which may be later retrieved by it (the client computer that stored the data) or other client computers for use in their processing operations. In addition, one or more of the server computers  12 ( m ) may, as “compute servers,” perform certain processing operations in response to a remote request therefor from a client computer  11 ( n ), and return the results of the processing to the requesting client computer  11 ( n ) for use by them (that is, the requesting client computers  11 ( n )) in their subsequent processing. In either case, the server computers may be generally similar to the client computers  11 ( n ), including a system unit, video display unit and operator input devices and may be usable by an operator for data processing operations in a manner similar to a client computer. Alternatively, at least some of the server computers may include only processing, memory, mass storage and network interface elements for receiving and processing retrieval, storage or remote processing requests from the client computers, and generating responses thereto. It will be appreciated a client computer  11 ( n ) may also perform operations described herein as being performed by a server computer  12 ( m ), and similarly a server computer  12 ( m ) may also perform operations described herein as being performed by a client computer  11 ( n ). 
     The network represented by communication link  14  may comprise any of a number of types of networks over which client computers  11 ( n ), server computers  12 ( m ) and nameserver computers  13  may communicate, including, for example, local area networks (LANs) and wide area networks (WANs) which are typically maintained within individual enterprises, the public telephony system, the Internet, and other networks, which may transfer digital data among the various computers. The network may be implemented using any of a number of communication media, including, for example, wires, optical fibers, radio links, and/or other media for carrying signals representing information among the various computers depicted in FIG.  1 . As noted above, each of the computers typically includes a network interface which connects the respective computer to the communications link  14  and allows it to transmit and receive information thereover. 
     Systems consistent with the present invention facilitate the obtaining and dynamic loading of “stub” information to enable a program operating in one address space to invoke processing of a remote method or procedure in another address space, which may be located on the same computer as the invoking program or on a different computer. Reference will be made to programs provided in the Java™ programming language, as described in James Gosling, Bill Joy, Guy Steele, “The Java™ Language Specification”, Addison-Wesley, 1996, (hereinafter referred to as the “Java language specification”), incorporated herein by reference, which are processed in connection with an execution environment which is provided by a Java virtual machine. The Java virtual machine, in turn, is specified in the Lindholm and Yellin, “The Java Virtual Machine Specification”, Addison-Wesley, 1996, incorporated herein by reference. As described in the Java language specification, programs in the Java programming language define “classes” and “interfaces.” Classes are used to define one or more methods or procedures, each of which may be invoked by reference to an interface. A class may be associated with and extend a “super-class,” and in that regard will incorporate all of the interfaces and methods of the super-class, and may also include additional interfaces and/or methods. A class may also have one or more sub-classes (and thus will comprise a super-class of each of its sub-classes), with each sub-class incorporating and possibly extending their respective super-classes. 
     An interface provides a mechanism by which a set of methods may be declared. In that connection, an interface identifies each method that is declared by the interface by, for example, a name, identities the data type(s) of argument(s) that are to be provided for the method, the data type(s) of return values that are to be returned by the method, and identifiers for exceptions which can be thrown during processing of the method. A class may indicate that it implements a particular interface, and in that connection will include the program code which will be used in processing all of the methods which are declared in the interface. In addition, different classes may indicate that they implement the same interface, and each will have program code which will be used in processing all of the methods which are declared in the interface, but the program code provided in each class to for use in processing the methods may differ from the program code provided in the other classes which is used in processing the same methods; thus, an interface provides a mechanism by which a set of methods can be declared without providing an indication of the procedure which will be used in processing any of the methods. An interface may be declared independently of the particular class which implements the method or methods which can be invoked using the interface. In that regard, a class that invokes the method and a class that actually implements the method will not need to share a common super-class. 
     During processing of a Java program, as described in the Java virtual machine specification, a client computer  11 ( n ) provides an execution environment  20  for interpreting the Java program. The Java virtual machine includes a class loader  21  that, under control of a control module  19 , can dynamically link instances of classes, generally identified in FIG. 1 by reference numeral  22 , into the running program&#39;s execution environment while the program is being executed. In that operation, the control module  19  effectively enables the class loader to retrieve uninstantiated classes, which generally identified by reference numeral  23 , instantiate them and link them as class instances  22  into the execution environment&#39;s address space at the Java program&#39;s run time as the methods which the respective classes  23  implement are called. In addition, the class loader  21  can discard ones of the class instances  22  when they are not needed or to conserve memory. It will be appreciated that, if a class instance  22  has been discarded, it may be reloaded by the class loader  21  at a later point if it is then needed. 
     Systems consistent with the present invention provide an arrangement which facilitates the remote invocation, by a program executing in an execution environment  20  by a client computer  11 ( n ), of methods implemented by classes on a server computer  12 ( m ). In executing a method, the server computer  12 ( m ) will also provide an execution environment  24  for processing, under control of a control module  28 , the Java method. In that operation, the Java virtual machine which provides the execution environment  21  includes a class loader  25  (which may be similar to the class loader  21 ) that, under control of the control module  28 , can dynamically link an instance of the class  26 , to enable the method to be processed in the execution environment  24 , and instances of other classes (also generally represented by reference numeral  26 ) which may be needed to process the remotely-invoked method. In that operation, the control module  28  effectively enables the class loader  25  to retrieve an uninstantiated class for the method to be invoked, from a plurality of uninstantiated classes which are generally identified by reference numeral  27 , instantiate it (that is, the uninstantiated class which provides the method to be invoked) and link it as a class instance  26  into the execution environment. In addition, the class loader  25  can discard the class instances  26  when processing of the method has terminated. It will be appreciated that, if class instances  26  has been discarded, it may be reloaded by the class loader  25  at a later point if it is then needed. 
     The structure of nameserver computer  13 , if provided, is generally similar to that of the server computer  12 ( m ), and will not be separately described. 
     To facilitate remote invocation of a method, the control module  19  of the client computer&#39;s execution environment  21  makes use of one or more stub class instances generally identified by reference numeral  30  which are provided as part of the execution environment  21  in which the various class instances  22 , including the class instance which is invoking the remote method, are being processed. Each stub class instance  30  is an instance of an uninstantiated stub class  31 , which the server computer  12 ( m ) may maintain for the various class instances  26  and uninstantiated classes  27  which the server computer  12 ( m ) has “exported,” that is, which the server computer  12 ( m ) makes available to client computers  11 ( n ) for use in remote invocation of methods provided thereby. An uninstantiated stub class  31  includes declarations for the complete set of interfaces for the particular remote uninstantiated class  27  which implements the remote method to be invoked, and also provides or invokes methods which facilitate accessing of the remote method(s) which are implemented by the remote class. The uninstantiated stub class  31 , when it is instantiated and provided to the execution environment  20  of the client computer  11 ( n ) as a stub class instance  30 , effectively provides the information which is needed by the control module  19  of the execution environment  20  of the invoking Java program, so that, when a remote method that is implemented by its associated class is invoked by a Java program running in a particular execution environment, the remote method will be processed and the return value(s) provided to the invoking Java program. In one embodiment, the arrangement by which the stub class instance may be provided to the execution environment  20  is similar to that described in the aforementioned Waldo, et al., patent application. 
     In addition, the server computer  12 ( m ) provides a skeleton  32 , which identifies the particular classes and methods which have been exported by the server computer  12 ( m ) and information as to how it (that is, the server computer  12 ( m )) may load the respective classes and initiate processing of the particular methods provided thereby. Additionally, the server computer  12 ( m ) contains a lookup service  400  for registering services on a network. The lookup service  400  will be discussed below. 
     When a class instance invokes a remote method maintained by a server computer  12 ( m ), it will provide values for various parameters to the stub class instance  30  for the remote method, which values the remote method will use in its processing. If the remote method is implemented on the same computer as the invoking Java program, when the invoking Java program invokes a remote method, the computer may establish an execution environment, similar to the execution environment  20 , enable the execution environment&#39;s class loader to load and instantiate the class which implements the method as a class instance similar to class instances  22 , and process the remote method using values of parameters which are provided by the invoking class instance in the remote invocation. After processing of the method has been completed, the execution environment in which the remote method has been processed will provide the results to the stub class instance  30  for the remote method that was invoked, which, in turn, will provide to the particular class instance  22  which invoked the remote method. 
     Similar operations will be performed if client computer  11 ( n ) and server computer  12 ( m ) are implemented on different physical computers. In that case, in response to a remote invocation, the client computer  11 ( n ) that is processing the invoking class instance  22 , under control of the control module  19  for the execution environment  20  for the invoking class instance  22 , will use the appropriate stub class instance  30  to communicate over the network represented by the communication link  14  with the server computer  12 ( m ) which implements the remote method to enable it (that is, the server computer  12 ( m )) to establish an execution environment  24  for the class which implements the remote method, and to use the class loader  25  to load an instance of the class as a class instance  26 . In addition, the client computer  11 ( n ), also using the appropriate stub class instance  30 , will provide any required parameter values to the server computer  12 ( m ) over the network  14 . Thereafter, the server computer  12 ( m ) will process the remote method using parameter values so provided, to generate result value(s) which are transferred over the network to the client computer  11 ( n ), in particular to the appropriate stub class instance  30 . The client computer  11 ( n ) will, after it receives the result value(s) from the network, provide them to the invoking class instance  22  for its processing. 
     In any case, when the control module  19  of the client computer&#39;s execution environment  20  determines that a reference to the remote object has been received, if it determines that the stub class instance  30  is not present when it receives the reference, it will attempt to obtain the stub class instance  30  from, for example, the server computer  12 ( m ) which implements the remote method, and enable the stub class instance  30  to be dynamically loaded in the execution environment  20  for the invoking class instance  22 . A reference to the remote object may be received, for example, either as a return value of another remote method invocation or as a parameter that is received during another remote method invocation. The stub class instance may be dynamically loaded into the execution environment in a manner similar to that used to load class instances  22  in the execution environment  22 . The execution environment  20  is provided with a stub class loader  33  which, under control of the control module  19 , will attempt to find and load the stub class instances  30  as required by the class instances  22  processed in the execution environment. The location of a particular server computer  12 ( m ) that maintains the class that implements a method to be invoked remotely may be included in the call from the invoking class instance or may be made known to the stub class loader  33  through another mechanism (not shown) maintained by the client computer  11 ( n ). 
     However, if the stub class loader  33  is not otherwise notified of which server computer  12 ( m ) maintains the class which implements a method which may be invoked remotely, it may use the nameserver computer  13  to provide that identification. The identification may comprise any identifier which may be used to identify a server computer  12 ( m ) or other resource which is available on the network  14  and to which the server computer  12 ( m ) can respond. Illustrative identifiers include, for example, a network address which identifies the server computer and/or resource, or, if the network  14  is or includes the Internet, an identifier to, for example, a World Wide Web resource which may provide the identification or a “uniform resource locator” (“URL”) which provides a uniform mechanism for identifying resources that are available over the Internet. The server computer  12 ( m ) which implements the remote method, in response to a request from the client computer  11 ( n ) will provide stub class instance  30  which the client computer  11 ( n ) may load into the execution environment  21  to thereafter enable the remote invocation to be initiated. 
     As noted above, if the stub class loader  33  does not know which server computer  12 ( m ) implements the remote method which may be invoked (and thus does not know which computer is to provide the stub class code for the remote invocation), it may, under control of the control module  19 , obtain the identification from the nameserver computer  13 . In that operation, the stub class loader  33  may use a previously-provided default stub class which is provided for use in such cases. The default class stub, when used by the invoking Java program, enables the computer that is processing the invoking Java program to communicate with the nameserver computer  13  to obtain information which can be used in invoking the remote method. This operation is essentially the same as the invocation of a remote method to be processed by the nameserver computer  13 , with the remote method including a parameter identifying the class and method to be remotely invoked, and enabling the nameserver computer  13  to provide the identification of a server computer  12 ( m ) which can process the method to the requesting client computer  11 ( n ) and other information which may be helpful in communicating with the server computer  12 ( m ) and invoking the particular method. It will be appreciated that the nameserver computer  13  will maintain a table (not separately shown) of “exported” resources, that is, resources, such as classes and methods, that are available to client computers  11 ( n ) connected to the network  14 , and information, such as the identifications of the particular server computers  12 ( m ) which provide those resources, which will be useful to the client computers  11 ( n ) in making use of the exported resources. 
     It will be appreciated that the nameserver computer  13  may create and maintain the exported resource table in a number of ways that are known in the art. For example, the nameserver computer  13  may periodically broadcast requests for exported resource information over the network  14 , to which the various server computers  12 ( m ) which maintain exported resources may respond; in that case, the nameserver computer  13  may establish its exported resource table based on the responses from the server computers  12 ( m ). Alternatively, each of the various server computers  12 ( m ) which maintains an exported resource may periodically broadcast information as to the exported resources which it maintains, and the nameserver computer  13  can update its exported resource table based on the broadcasts from the server computer. In addition, the nameserver computer&#39;s exported resource table may be established by a system operator and may be fixed until he or she updates it. 
     In any case, the information provided by the nameserver computer  13  in response to a request initiated by the default stub would include such information as, for example, the identification of a computer  12 ( m ) which can provide a class which implements the remote method to be invoked, particular information which the computer (that is, the computer which implements the remote method) will require to provide the required stub class code, and the like. After receiving the information from the nameserver computer  13 , the computer  11 ( n ) that is processing the invoking Java program may, under control of the control module  19 , use the information communicate with the computer (that is, the computer which implements the remote method) to obtain the stub class, and may thereafter invoke the method as described above. 
     With this background, the operations performed by client computer  11 ( n ), server computer  12 ( m ) and, if necessary, nameserver  13  in connection with obtaining and dynamic loading of a stub class instance when a reference to a remote method is received will be described in connection with the flow chart depicted in FIG.  2 . In addition, operations performed by the client computer  11 ( n ) and server computer in connection with remote invocation of a method using the stub class instance will be described in connection with the flow chart depicted in FIG.  3 . With reference initially to FIG. 2, the execution environment control module  19  will, when it receives a reference to a remote method, will initially determine whether an appropriate stub class instance is present in the execution environment  20  to facilitate invocation of the remote method (step  100 ). If the control module  19  determines that such a stub class instance  30  for the remote method is present in the execution environment, it may continue other operations (step  101 ). However, if the control module  19  determines in step  101  that such a stub class instance is not present in the execution environment  20  for the remote method, the control module  19  will use the stub class loader  33  to attempt to locate and load a stub class instance  30  for the class to process the remote method. In that case, the control module  19  will initially determine whether the invocation from the class instance  22  included a resource locator to identify the server computer  12 ( m ) or other resource which maintains the class for the method to be invoked, or whether it (that is, the control module  19 ) or the stub class loader  33  otherwise are provided with such a resource locator (step  102 ). If the control module  19  makes a positive determination in that step, it will sequence to step  103  to enable the stub class loader  33  to initiate communications with identified server computer  12 ( m ) to obtain stub class instance for the class and method to be invoked (step  103 ). When the stub class loader  33  receives the stub class instance  30  from the server computer  12 ( m ), it will load the stub class instance  30  into execution environment  20  for the class instance  22  which initiated the remote method invocation call in step  100  (step  104 ). After the stub class instance  30  for the referenced remote method has been loaded in the execution environment, the method can be invoked as will be described below in connection with FIG.  3 . 
     Returning to step  102 , if the control module  19  determines that the invocation from the class instance  22  did not include a resource locator to identify the server computer  12 ( m ) or other resource which maintains the class for the method to be invoked, and further that it (that is, the control module  19 ) or the stub class loader  33  is not otherwise provided with such a resource locator, a “class not found” exception may be indicated, at which point the control module  19  may call an exception handler. The exception handler may perform any of a number of recovery operations, including, for example, merely notifying the control module  19  that the remote method could not be located and allow it to determine subsequent operations. 
     Alternatively, the control module  19  may attempt to obtain a resource locator from the nameserver computer  13  or other resource provided by the network  14  (generally represented in FIG. 1 by the nameserver computer  13 ), using a call, for example, a default stub class instance  30 . The call to the default stub class instance  30  will include an identification of the class and method to be invoked and the name of the nameserver computer  13 ( m ). Using the default stub class instance  30 , the control module  19  will enable the computer  11 ( n ) to initiate communications with nameserver computer  13  to obtain an identifier for a server computer  12 ( m ) which maintains the class and method to be invoked (step  110 ). The communications from the default stub class instance  30  will essentially correspond to a remote method invocation, with the method enabling the nameserver computer to provide the identification for the server computer  12 ( m ), if one exists associated with the class and method to be remotely invoked, or alternatively to provide an indication that no server computer  12 ( m ) is identified as being associated with the class and method. During the communications in step  110 , the default stub class interface  30  will provide, as a parameter value, the identification of class and method to be invoked. 
     In response to the communications from the default stub class instance  30 , the nameserver computer  13  will process the request as a remote method (step  111 ), with the result information comprising the identification for the server computer  12 ( m ), if one exists that is associated with the class and method to be remotely invoked, or alternatively an indication that no server computer  12 ( m ) is identified as being associated with the class and method. After finishing the method, the nameserver computer  13  will initiate communications with the default stub class instance  30  to provide the result information to the default stub class instance  30  (step  112 ). 
     After receipt of the result information from the nameserver computer  13 , the default stub class instance, under control of the control module  19 , will pass result information to the stub class loader  33  (step  113 ). Thereafter, the stub class loader  33  determines whether the result information from the nameserver computer comprises the identification for the server computer  12 ( m ) or an indication that no server computer  12 ( m ) is identified as being associated with the class (step  114 ). If the stub class loader  33  determines that the result information comprises the identification for the server computer  12 ( m ), it (that is, the stub class loader  33 ) will return to step  101  to initiate communication with the identified server computer  12 ( m ) to obtain stub class instance for the class and method that may be invoked. On the other hand, if the stub class loader  33  determines in step  114  that the nameserver computer  13  had provided an indication that no server computer  12 ( m ) is identified as being associated with the class and method that may be invoked, the “class not found” exception may be indicated (step  115 ) and an exception handler called as described above. 
     As noted above, the stub class instance  30  retrieved and loaded as described above in connection with FIG. 2 may be used in remote invocation of the method. Operations performed by the client computer  11 ( n ) in connection with remote invocation of the method will be described in connection with the flow chart in FIG.  3 . As depicted in FIG. 3, when a class instance  22  invokes a method, the control module  19  may initially verify that a stub class instance  30  is present in the execution environment for remote method to be invoked (step  120 ). If a positive determination is made in step  120 , the stub class instance  30  will be used for the remote invocation, and in the remote invocation will provide parameter values which are to be used in processing the remote method (step  121 ). Thereafter, the stub class instance  30  for the remote method that may be invoked will be used to initiate communications with the server computer  12 ( m ) which maintains the class for the remote method (step  122 ), in the process, the passing parameter values which are to be used in processing the remote method will be passed. It will be appreciated that, if the server computer  12 ( m ) which is to process the method is the same physical computer as the client computer  12 ( n ) which is invoking the method, the communications can be among execution environments which are being processed within the physical computer. On the other hand, if the server computer  12 ( m ) which is to process the method is a different physical computer from that of the client computer  12 ( n ) which is invoking the method, the communications will be through the client computer&#39;s and server computer&#39;s respective network interfaces  15 ( n ) and  16 ( m ) and over the network  14 . 
     In response to the communications from the stub class instance in step  122 , the server computer  12 ( m ), if necessary establishes an execution environment  24  for the class which maintains the method that may be invoked, and the uses the information provided by the skeleton  32  to create a class instance  26  for that class (step  123 ). Thereafter, the server computer  12 ( m ), under control of the control module  28 , will process the method in connection with parameter values that were provided by stub class instance  30  (step  124 ). After completing processing of the method, the server computer  12 ( m ), also under control of the control module  28 , will initiate communications with the client computer&#39;s stub class instance  30  to provide result information to the stub class instance (step  125 ). In a manner similar to that described above in connection with step  102 , if the server computer  12 ( m ) which processed the method is the same physical computer as the client computer  12 ( n ) which invoked the method, the communications can be among execution environments  24  and  20  which are being processed within the physical computer. On the other hand, if the server computer  12 ( m ) which processed the method is a different physical computer from that of the client computer  12 ( n ) which is invoking the method, the communications will be through the server computer&#39;s and client computer&#39;s respective network interfaces  16 ( m ) and  15 ( n ) and over the network  14 . After the stub class instance  30  receives the result information from the server computer, it may provide result information to the class instance  22  which initiated the remote method invocation (step  126 ), and that class instance  22  can continue processing under control of the control module  19 . 
     Returning to step  120 , if the control module  19  determines in that step that it does not have a stub class instance  30  that is appropriate for the remote method that may be invoked, it may at that point call an exception handler (step  127 ) to perform selected error recovery operations. 
     Methods and systems consistent with the present invention provide a number of advantages. In particular, they provide a new system and method for facilitating dynamic loading of a stub which enables a program that is operating in one execution environment to remotely invoke processing of a method in another execution environment, so that the stub can be loaded by the program when it is run and needed. In systems in which stubs are compiled with the program, and thus are statically determined when the program is compiled, they (the stubs) may implement subsets of the actual set of remote interfaces which are supported by the remote references that is received by the program, which can lead to errors and inefficiencies due to mismatches between the stub that is provided to a program and the requirements of the remote procedure that is called when the program is run. However, since, in the dynamic stub loading system and method, the stub that is loaded can be obtained from the particular resource which provides the remote method, it (the stub) can define the exact set of interfaces to be provided to the invoking program at run time, thereby obviating run-time incompatibilities which may result from mismatches between the stub that is provided and the requirements of the remote method that is invoked. 
     It will be appreciated that a number of modifications may be made to the arrangement as described above. For example, although the execution environment  20  has been described as obtaining and loading stub class instances to facilitate invocation of remote methods when references to the remote methods are received, it will be appreciated that stub class instances may instead be obtained and loaded when the remote methods are initially invoked. Obtaining and loading of the stub class instance for a remote method when a reference thereto is received will have the advantages that (I) the stub class instance will be present in the execution environment when the remote method is actually invoked, and (ii) if the appropriate stub class instance can not be located, the program or an operator may be notified at an early time. On the other hand, obtaining and loading of the stub class instance for a remote method when the method is to be invoked may result in a delay of the invocation until the correct stub class instance can be found, if the method is in fact not invoked even if a reference to it is received the stub class instance may not need to be located and loaded. 
     It will be appreciated that a system in accordance with the invention can be constructed in whole or in part from special purpose hardware or a general purpose computer system, or any combination thereof, any portion of which may be controlled by a suitable program. Any program may in whole or in part comprise part of or be stored on the system in a conventional manner, or it may in whole or in part be provided in to the system over a network or other mechanism for transferring information in a conventional manner. In addition, it will be appreciated that the system may be operated and/or otherwise controlled by means of information provided by an operator using operator input elements (not shown) which may be connected directly to the system or which may transfer the information to the system over a network or other mechanism for transferring information in a conventional manner. 
     Alternative Embodiment of the Present Invention 
     Although an embodiment consistent with the present invention has been previously described that dynamically retrieves and loads stubs, an alternative embodiment also consistent with the present invention loads and retrieves objects in a lookup service, where the objects contain code (stub information) for facilitating communication with a particular service or the objects contain code that performs the service. Although the alternative embodiment is described below as downloading objects from the lookup service that represent stubs, the techniques described below are equally applicable to downloading objects that actually perform the services. A lookup service defines a network&#39;s directory of services and stores references to these services. A user desiring use of a service on the network accesses the lookup service, which returns the stub information that facilitates the user&#39;s access of the service. 
     The lookup service may contain a subset of all services available in the network, referred to as a “Djinn” as described in copending U.S. patent application Ser. No. 09/044,931, entitled “Dynamic Lookup Service in a Distributed System,” assigned to a common assignee, filed on even date herewith, which has been previously incorporated by reference. A “Djinn” refers to a logical grouping of one or more of the services or resources that are provided by a network. Devices connected to the network may either dynamically add themselves to the Djinn or dynamically remove themselves from the Djinn. When added, a device provides zero or more of its services to the Djinn and may utilize all of the services currently provided by the Djinn. The services provided by the Djinn are defined by the lookup service, which provides a common way to both find and utilize the services for the Djinn. 
     The lookup service is a fundamental part of the infrastructure for a Djinn or other computer network offering a range of services. It is the primary means for programs to find services available within the Djinn and is the foundation for providing stubs through which users and administrators can discover and interact with services in the Djinn. 
     Reference will now be made to FIG. 4, which depicts lookup service  400  in greater detail. Server computer  12 ( m ), also includes a lookup service  400 , further described below. The lookup service  400 , located on a server  12 ( m ) as shown in FIG. 1, maintains a collection of “service items”  410 - 418 . Each service item  410 - 418  represents an instance of a service available within the Djinn, and each service item  410  contains a service ID  402  that uniquely identifies the service item, a stub  404  providing code that programs use to access the service, and a collection of attributes  406  that describe the service. 
     Upon registering a new service with the lookup service  400 , the lookup service gives the new service item  410  a unique service ID  402 , typically a number. This service ID  402  can later be used to access the specific service, avoiding unnecessary searching or locating several matching service items upon a query. 
     When a new service is created (e.g., when a new device is added to the Djinn), the service registers itself with the lookup service  400 , providing a stub  404  to be used by a client to access the service and an initial collection of attributes  406  associated with the service. For example, a printer might include attributes indicating speed (in pages per minute), resolution (in dots per inch), color, and whether duplex printing is supported. The lookup service administrator (not shown) might also add new attributes, such as the physical location of the service and common names for it. Additionally, if a service encounters some problem that needs administrative attention, such as a printer running out of toner, the service can add an attribute that indicates what the problem is. In one implementation consistent with the present invention, attributes are stored as multi-entries, and the addition, modification and deletion of attributes can be made using multi-templates and the techniques explained in co-pending U.S. patent application Ser. No. 09/044,839, entitled “Method and System for In-Place Modifications In A Database”, previously incorporated herein. 
     An individual set of attributes is represented as an instance of a class, each attribute being a field of that class. An example of an attribute set for a printer is: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 public class Printer { 
               
            
           
           
               
               
               
               
            
               
                   
                 Integer ppm; 
                 // 
                 pages per minute 
               
               
                   
                 Integer dpi; 
                 // 
                 resolution in dots per inch 
               
               
                   
                 Boolean duplex; 
                 // 
                 supports two-sided printing 
               
               
                   
                 Boolean color; 
                 // 
                 color or black-only 
               
            
           
           
               
            
               
                 } 
               
               
                   
               
            
           
         
       
     
     The class provides strong typing of both the set and the individual attributes. 
     The attributes  406  of service items  410  can also be represented as a set of sets of attributes. Attributes  406  of a service item  410  can contain multiple instances of the same class with different attribute values, as well as multiple instances of different classes. For example, the attributes  406  of a service item  410  might have multiple instances of a Name class, each giving the common name of the service in a different language, plus an instance of a Location class, a Type class, or various other service-specific classes. An example of some added attributes to describe the printer may be the Name, Type, or Location: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 public class Name implements Entry { 
               
            
           
           
               
               
               
               
            
               
                   
                 String name; 
                 // 
                 the user-friendly name of the service 
               
               
                   
                 String description; 
                 // 
                 free-form description of the service 
               
               
                   
                 String language; 
                 // 
                 language (e.g., English, French) used 
               
            
           
           
               
            
               
                 in the above 
               
               
                 } 
               
            
           
           
               
               
            
               
                   
                 public class Type implements Entry { 
               
            
           
           
               
               
               
               
            
               
                   
                 String type; 
                 // 
                 the general type of service 
               
               
                   
                 String vendor; 
                 // 
                 vendor of product that implements 
               
            
           
           
               
            
               
                 the service 
               
            
           
           
               
               
               
               
            
               
                   
                 String model; 
                 // 
                 model number/name of product 
               
               
                   
                 String version; 
                 // 
                 version number of product 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                   
                 public class Location implements Entry { 
               
            
           
           
               
               
               
               
            
               
                   
                 Integer floor; 
                 // 
                 what floor the service is on 
               
               
                   
                 String building; 
                 // 
                 what building it&#39;s in 
               
               
                   
                 String room; 
                 // 
                 what room it&#39;s in 
               
            
           
           
               
            
               
                 } 
               
               
                   
               
            
           
         
       
     
     In this example, the attributes  406  for this service item  410  would be a set of attributes containing the Printer, Name, Type, and Location class instances, each class containing their own individual attributes. However, it should be noted that the scheme used for attributes is not constrained by these examples. 
     Programs (including other services) that need a particular type of service can use the lookup service  400  to find a stub that can be used to access the service. A match can be made based on the type of service as well as the specific attributes attached to the service. For example, a client could search for a printer by requesting a stub type corresponding to the service desired or by requesting certain attributes such as a specific location or printing speed. In one implementation consistent with the present invention, attributes are stored as multi-entries, and a match on attributes can be made using multi-templates, as explained in co-pending U.S. patent application Ser. No. 09/044,835, entitled “Method and System For Multi-Entry and Multi-Template Matching In A Database”, previously incorporated herein. 
     Accessing a Lookup Service Employing Dynamic Stub Loading and Retrieval 
     Referring back to FIG. 4, the stub  404  corresponding to a service is registered in the lookup service  400  and is used by the client computer  11 ( n ) to access the service methods remotely. This stub  404  may also be a “smart proxy.” A smart proxy, code within which a stub is embedded, helps the client more efficiently implement the stub and the method to be remotely invoked. A smart proxy often performs some local computation for efficiency before or after it actually calls the stub. For example, a smart proxy may contain code to cache information, so if a client requested it again, instead of going back to the server to get the information, it may have cached the answer and be able to return it quickly. If the situation called for it, a smart proxy might also transform the parameters received from the client into other types and then send the transformed types. The smart proxy concept is further explained in co-pending U.S. patent application Ser. No. 09/044,930, entitled “Downloadable Smart Proxies for Performing Processing Associated with a Remote Procedure Call in a Distributed System,” assigned to a common assignee, filed on even date herewith, which is hereby incorporated by reference. 
     FIG. 5 depicts a flowchart illustrating the steps used by systems consistent with the present invention for adding a service stub to the lookup service. When a device joins the network, it typically registers a service with the lookup service (step  500 ). Upon registration with the lookup service  400 , the device supplies a stub  404  to the lookup service, and it may also give its associated attributes  406  to the lookup service (step  502 ). In response, the lookup service  400  assigns a unique service ID  402 , typically a number as previously stated, to the service registered with the lookup service (step  504 ). Once the device has supplied the lookup service  400  with a stub  404  and attributes  406 , and the lookup service has assigned a unique service ID  402 , the device has completed registration of the service with the lookup service (step  506 ). After services are registered with the lookup service  400 , clients can use the lookup service to obtain stub information needed to access the registered services. 
     FIG. 6 depicts a flowchart illustrating steps used by systems and methods consistent with the present invention to download a service item from the lookup service. In one implementation, the client computer  11 ( n ) sends a request for a service to the server  12 ( m ) with the lookup service  400  (step  600 ). The request originates from the remote method invocation of a class instance  22  on client computer  11 ( n ), and the requested service may reside on a remote server as the exemplary service  38  resides on server  12 (I). In one implementation consistent with the present invention, the client computer  11 ( n ) may request one or more services from the lookup service  400 . The client&#39;s request comes in the form of a specific service ID  402 , a type of stub  404 , or a set of attributes  406 , or any combination thereof (step  602 ). In response to the request, control  19  directs the stub class loader  33  to locate the corresponding stub  404  from the server  12 ( m ). To do so, the control  19  enables the stub class loader  33  to initiate communication with the server  12 ( m ) to obtain a stub  404  for the service to be obtained. 
     Upon receipt of the request from the client computer  11 ( n ), the control  28  in the server  12 ( m ) searches the lookup service  400  for the stub  404  corresponding to the requested service (step  604 ). If there are no matches found, the control  28  returns a null value (steps  606  and  608 ). Otherwise, if it locates the stub  404  corresponding to the service that the client computer  11 ( n ) is attempting to access, the server  12 ( m ) returns the stub to the stub class loader  33  on the client computer (step  612 ). If more than one stub was located matching the client&#39;s request (step  610 ), in one embodiment consistent with the present invention, any one of the stubs is returned (step  616 ). In another implementation where the client requests more than one service, the server  12 ( m ) returns the requested number of the stubs with their attributes (steps  614  and  618 ). 
     When the stub  404  is received by the stub class loader  33 , the stub class loader loads it into the execution environment  20 . After it is loaded, the service  38  can be remotely invoked. The use of the stub information to invoke remote processing of the service  38  is performed in the same manner as previously discussed in connection with FIG.  3 . 
     Generally, the class instance  22  can use the stub  404  to access the service  38  on the server  12 (I). When the class instance  22  requires use of the service  38  corresponding to the returned stub  404 , control  19  verifies that the stub  404  is present in the execution environment  20 . If so, the class instance  22  can then use the stub  404  to initiate communications with the server  12 (I) that maintains the service  38 , and parameters will be passed to the service  38  for implementation. 
     This lookup service implementation is one application of the dynamic loading and retrieval of stub information to enable a program operating in one address space to invoke processing of a procedure in another address space. This implementation of using the dynamic stub loading on the lookup service allows a client to receive stub information to facilitate use of that service directly. Unlike previous lookup services, the lookup service consistent with the present invention returns the code needed to access the service directly. Using the dynamic loading of stub information in this way allows the client to receive all the code necessary to facilitate use of the service on a remote server. 
     Second Alternative Embodiment of the Present Invention 
     In accordance with a second alternative embodiment of the present invention, a network proxy is provided that enables orphan services to utilize the lookup service and become integrated into the network environment previously described. An “orphan service” runs on a device that typically has too little memory to support the Java™ runtime system, including the Java™ Virtual Machine and Remote Method Invocation (RMI), discussed further below. To integrate such services into the network environment, the network proxy facilitates lookup-service registration and manages resource allocation on behalf of the services. The network proxy thus integrates devices with limited capabilities, as well as their services, into the network environment described above with little retrofitting. 
     FIG. 7 depicts a data processing system  700  suitable for use with this embodiment. Data processing system  700  includes a lookup server  702 , a computer  704 , a device  706 , and a proxy server  708 , all of which are interconnected via a network  709 . Lookup server  702  includes a memory  710  containing lookup service  400  and Java™ Runtime System (JRS)  736  and also includes other standard components, such as secondary storage, a CPU, a video display, and an input device. JRS  736  includes the Java™ Virtual Machine (JVM)  738  and RMI  740 . JRS  736 , JVM  738 , and RMI  740  are provided as part of the Java™ software development kit available from Sun Microsystems of Mountain View, Calif. JVM  738  facilitates platform independence by acting like an abstract computing machine, receiving instructions from programs in the form of byte codes and interpreting these byte codes by dynamically converting them into a form for execution, such as object code, and executing them. RMI  740  facilitates remote method invocation by allowing objects executing on one computer or device to invoke methods of an object on another computer or device. 
     Computer  704  includes a memory  712  containing a client program  714  and JRS  742  and includes other standard components. Device  706  includes a memory  716  containing a protocol stack  720  as well as an orphan service  721  and also includes a CPU  718 . Proxy server  708  includes a memory  722  containing a network proxy  726 , a protocol stack  728 , and JRS  730  and also includes other standard components. Network proxy  726  is responsible for registering orphan service  721  in lookup service  400  so that client program  714  can utilize the orphan service. Additionally, network proxy  726  provides orphan service  721  with access to various other services provided via lookup service  400 . 
     FIG. 8 depicts a flowchart of the steps performed when the network proxy registers the orphan service with the lookup service so that the client program may utilize it. The first step performed is for the network proxy to obtain a reference. to the lookup service (step  802 ). This step is performed by accessing the discovery server as described in co-pending U.S. patent application Ser. No. 09/044,939, entitled “Apparatus and Method for Providing Downloadable Code for Use in Communicating with a Device in a Distributed System,” filed on Mar. 20, 1998, assigned to a common assignee, which has previously been incorporated by reference. After obtaining a reference to the lookup service, the network proxy utilizes protocol stack  728  to communicate with the orphan service via protocol stack  720  (step  804 ). In this step, the network proxy and the orphan service enter into a peer-to-peer communication session using a protocol such as TCP/IP. During this session, the orphan service provides the network proxy with sufficient information to construct a stub (or object) for registration in the lookup service as previously described. This information, typically stored on the device (e.g., PROM), includes the code for the object, in the form of byte codes, as well as the Java™ programming language object type. Next, the network proxy registers this object in the lookup service as described above (step  806 ). 
     After the network proxy registers the orphan service, the client program may access the lookup service to retrieve the object that was registered (step  808 ). After retrieving the object, the client program can communicate with and utilize the orphan service by invoking the methods on the object (step  810 ). In this step, the methods of the object registered in the lookup service may communicate directly with the orphan service if the device resides on the same type of network as the client program. Otherwise, if the client resides on a different type of network, the methods may communicate with the network proxy, who will in turn perform a protocol conversion and use the protocol stack to communicate with the orphan service. 
     FIG. 9 depicts a flow chart of the steps performed by an alternative embodiment when the network proxy registers the orphan service with the lookup service so that the client program may utilize it. In this embodiment, the code for the object is stored remotely with respect to the device. For example, the code may be stored on the proxy server. Since the it code is not stored on the device, a peer-to-peer communication session is not necessary, thus relieving the need for the proxy server to utilize a protocol stack and anything else specific to the device, such as a device driver, and allowing the code to be modified without having to access the device. As a result, if the code were burned in PROM, significant processing would be avoided. 
     In this embodiment, the orphan service broadcasts a multicast packet to a predefined port on the devices on the network (step  902 ). The network proxy listens on this port and receives the multicast packet containing a location identifier, such as a URL, indicating a location on the network of where the object is located and the object type. The network proxy then responds to the device indicating a successful receipt of the packet (step  904 ). After receiving the location identifier and the object type, the network proxy registers the orphan service in the lookup service (step  906 ). In this step, the network proxy may access the object at the specified location and store both the object as well as an indication of its type in the lookup service. Alternatively, the network proxy may store the location identifier and the object type in the lookup service. In this case, when the client program requests the object from the lookup service, RMI retrieves the entry in the lookup service, containing the location identifier (e.g., the URL), accesses the object at that location, and returns the object to the client program, as previously described. Later, the client program may access the object that is either stored in or referenced in the lookup service and communicate directly with the orphan service as stated above (step  908 ). 
     FIG. 10 depicts a flow chart of the steps performed by the network proxy when managing services on behalf of an orphan service. The first step performed is for the network proxy to receive a request from the orphan service for use of another service identified in the request (step  1002 ). In this step, the network proxy receives the request by listening on the predefined port or by receiving a packet via the protocol stack, depending on the embodiment used. Responsive to this request, the network proxy obtains an object representing the requested service from the lookup service, as previously described, entering into a lease (step  1004 ). Services in the lookup service are utilized on a lease basis, meaning that the client who is requesting use of the service requests its use for a particular time period, and the service then determines whether it will allow a lease for (1) the entire requested period, (2) less than the entire requested period, or (3) not at all. Leasing of services and resources is further described in copending U.S. patent application Ser. No. 09/044,923, entitled “Method and System for Leasing Storage,” U.S. patent application Ser. No. 09/044,838, entitled “Method, Apparatus, and Product for Leasing of Delegation Certificates in a Distributed System,” U.S. patent application Ser. No. 09/044,834, entitled “Method, Apparatus, and Product for Leasing of Group Membership in a Distributed System,” and U.S. patent application Ser. No. 09/044,916, entitled “Leasing for Failure Detection,” all of which have been previously incorporated by reference. The network proxy may then receive requests from the orphan service to manipulate the object and the network proxy responds by manipulating the object accordingly, thus making use of the requested service (step  1006 ). In this situation, the network proxy may renew the lease when it is near expiration and may cancel the lease when the orphan service has completed its use of the requested service. 
     Although aspects of the present invention are described as being stored in memory, one skilled in the art will appreciate that these aspects can also be stored on or read from other types of computer-readable media, such as secondary storage devices, like hard disks, floppy disks, or CD-ROM; a carrier wave from a network, such as the Internet; or other forms of RAM or ROM either currently known or later developed. Sun, Sun Microsystems, the Sun logo, Java™, and Java™-based trademarks are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries. 
     The foregoing description has been limited to specific embodiments of the present invention. It will be apparent, however, that various variations and modifications may be made. It is the object of the appended claims to cover these and such other variations and modifications as come within the true spirit and scope of the invention.