Abstract:
A technique is provided for allowing the implementation of Advanced Web Services on a legacy platform. Logical work is separated into modules and the target platform is abstracted through a simple abstract interface. The implementation of one or more Web Services specifications is packaged into a common module (that may be dynamically or statically loaded) so that the complexity of the Web Services is hidden from developers. Also, SOAP and/or WSDL standards may be packaged and implemented into common modules. Developers may create new services while relying on the common modules.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. patent application Ser. No. 11/641,453 filed on Dec. 18, 2006, entitled “WEB SERVICES DEVICE PROFILE ON A MULTI-SERVICE DEVICE: DYNAMIC ADDITION OF SERVICES”. 
   This application is related to U.S. patent application Ser. No. 11/641,454 filed on Dec. 18, 2006, entitled “WEB SERVICES DEVICE PROFILE ON A MULTI-SERVICE DEVICE: DEVICE AND FACILITY MANAGER”. 
   FIELD OF THE INVENTION 
   The present invention relates to providing Web services, and more particularly to implementing standard Web service protocol on a legacy platform by separating logical work into separate modules. 
   BACKGROUND 
   The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
   The term “Web services” describes a standardized way of integrating Web-based applications using the Extensible Markup Language (XML), Simple Object Access Protocol (SOAP), Web Services Description Language (WSDL) standards over an Internet protocol Backbone. XML is used to tag the data, SOAP is used to transfer the data, and WSDL is used for describing the services available. Used primarily as a means for businesses to communicate with each other and with clients, Web services allow organizations to communicate data without intimate knowledge of each other&#39;s IT systems behind a firewall. 
   Web services share business logic, data, and processes through a programmatic interface across a network. Web services allow different applications from different sources to communicate with each other without time-consuming custom coding. And, because all communication is in XML, Web services are not tied to any one operating system or programming language. For example, Java can talk with Python and Windows applications can talk with UNIX applications. 
   Web Services specifications compose together to provide interoperable protocols for Security, Reliable Messaging, and Transactions in loosely coupled systems. Web Services specifications include both approved standards (e.g. by the World Wide Web Consortium (W3C) and the Organization for the Advancement of Structured Information Standards (OASIS)) and proposed documents and drafts that may become standards. 
   Many Web Services specifications, in addition to specifications that are planned to be released in the next few years, are relatively complex. Implementing each specification requires complicated development and a high level of expertise from application developers. Furthermore, as more Web Services specifications become standardized, an increasing number of application developers will be unable to develop applications that take full advantage of the additional Web Services specifications. 
   SUMMARY 
   An approach is provided for implementing Web Services on a legacy platform. A first Web service application (WSA) receives a SOAP request for a first service. A portion of the SOAP request conforms to a Web Services specification. A library routine from a shared library is invoked based on the portion. The library routine implements one or more functions defined by the Web Services specification. Based on results from the library routine, a device-specific request is generated that conforms to a communications protocol supported by a multi-functional peripheral (MFP) that may include a print process for processing print data and causing a printed version of an electronic document reflected in the print data to be generated. The device-specific request is then transmitted to the MFP. 
   A second WSA receives a SOAP request for a second service. A portion of the SOAP request conforms to the same Web Services specification. A library routine from the shared library is invoked based on that portion. Based on results from this library routine, a second device-specific request is generated and transmitted to the MFP. 
   In one approach, a SOAP library routine is invoked that analyzes the first SOAP request and identifies one or more Web Services specifications that are specified in the SOAP request. Results from the SOAP library routine are received at the first WSA. Thus, invoking the library routine is based on the results from the SOAP library routine. 
   In one approach, the SOAP library routine is shared with the second WSA. 
   In one approach, if the SOAP request comprises a plurality of portions, then results from the SOAP library routine comprise a plurality of identifiers that each indicate a Web Services specification to which the corresponding portion conforms. 
   In one approach, a different portion of the SOAP request conforms to a different Web Services specification. Therefore, a different library routine corresponding to the different portion is invoked, from which results are received. 
   In one approach, another library routine is added to the shared library, wherein the added library routine implements one or more functions defined by a different Web Services specification. Thus, the first and second WSAs may invoke the added library routine if a portion of a subsequent SOAP request conforms to the different Web Services specification. 
   In one approach, a WSA includes an abstract API that is used to generate the device-specific request. The abstract API defines an interface by which the WSA invokes one or more functions on the MFP. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  is a flow diagram that illustrates an approach for processing requests to process data on multi-functional peripherals (MFPs), according to an embodiment of the invention; 
       FIG. 2  is a block diagram that illustrates an example architecture for processing requests to process data on MFPs, according to an embodiment of the invention; 
       FIG. 3  is a sequence diagram illustrating an example of how a SOAP request for a printing service may be processed, according to an embodiment of the invention and 
       FIG. 4  is a block diagram that illustrates a computer system upon which an embodiment of the invention may be implemented. 
   

   DETAILED DESCRIPTION 
   In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
   Functional Overview 
     FIG. 1  is a flow diagram that illustrates an approach for processing requests to process data on multi-functional peripherals (MFPs), according to one embodiment of the invention. As used herein, the term MFP refers to a device that performs one or more functions, such as printing, copying, facsimile and scanning.  FIG. 1  depicts the approach in the context of processing a SOAP request for a device provided by an MFP, although the approach is not limited to the SOAP context. At step  102 , a SOAP request for a first service is received at a first web service application. The SOAP request is composed to request a Web service that implements one or more Web Services specifications. A portion of the SOAP request conforms to a first Web Services specification. At step  104 , a library routine is invoked from a shared library based on the portion of the SOAP request. The library routine implements one or more functions defined by the first Web Services specification. At step  106 , results are received from the library routine. At step  108 , a device-specific request is generated based on the results. The device-specific request conforms to a communications protocol supported by a multi-functional peripheral (MFP). The MFP may include a print process for processing print data and causing a printed version of an electronic document reflected in the print data to be generated. At step  110 , the device-specific request is transmitted to the MFP. 
   At step  112 , a second SOAP request for a second service is received at a second web service application. A portion of the second SOAP request conforms to the Web Services specification. At step  114 , the same library routine is invoked from the shared library based on the portion of the second SOAP request. At step  116 , results are received from the library routine invoked in step  114 . At step  118 , a second device-specific request is generated based on the results received in step  116 . The second device-specific request also conforms to the communications protocol. At step  120 , the second device-specific request is transmitted to the MFP. 
   Architectural Overview 
     FIG. 2  is a block diagram that illustrates an example architecture  200  for processing requests to process data on MFPs, according to one embodiment of the invention. Architecture  200  includes a requesting application  202 , a Web services application  204  and  206 , a SOAP software development kit (SDK) module (SSM)  208 , a Web Services protocol module (WSPM)  210 , and a network  220 , according to an embodiment of the invention. Requesting application  202  is an application that requests a Web service using the SOAP protocol. Web services application (WSA)  204  receives requests for one or more Web services. SSM  208  provides, to WSA  204  and WSA  206 , library routines to analyze SOAP messages and generate SOAP messages. WSPM  210  provides library routines, corresponding to one or more Web Services specifications, to WSA  204  and WSA  206 . 
   For example, requesting application  202  sends a SOAP request (e.g. over network  220 ) to WSA  204 . By definition, the SOAP request comprises a header section and a body section. The header section comprises one or more portions, each corresponding to and requiring a standard Web Services protocol, such as WS-Security. If WSA  204  is not configured to analyze SOAP messages, then WSA  204  may invoke a SOAP library routine provided by SSM  208  in order to understand the structure of the SOAP request. The results of invoking the SOAP library routine on the SOAP request includes 1) an indication that the SOAP request is valid and 2) a set of identifiers that identify one or more Web Services specifications that are specified in the SOAP request. 
   Based on the results, WSA  204  invokes at least one library routine from WSPM  210  which acts as a shared library. The library routine implements one or more functions defined by a Web Services specification. Based on the results from invoking the library routine, WSA  204  generates a device-specific request that conforms to a communications protocol supported by a MFP (e.g. using an abstract API via Abstract API  214 ). WSA  204  then transmits the device-specific request to the MFP. 
   If requesting application  202  requires the service(s) provided by WSA  206 , then WSA  206  may also utilize the library routines provided by SOAP SDK  208  and WSPM  210 . 
   Requesting Application 
   Requesting application  202  is an application that is associated with a process that requests a particular Web service provided by WSA  204  or WSA  206 . Requesting application  202  is typically an application associated with the operating system that supports the initial requesting process. A purpose of requesting application  202  is to convert a platform-specific procedure call, from a requesting process, to a SOAP request that can be processed by an application that “understands” SOAP. On the other hand, requesting application  202  may be a GUI that a user interacts with. In this case, requesting application  202  converts user clicks into SOAP requests. 
   For example, the requesting process may be associated with a Microsoft Word application and WSA  204  may be a print application. Requesting application  202  receives a platform-specific “print data” request sent from the requesting process. Requesting application  202  encodes the print data request in a SOAP message that can be processed by WSA  204  that “understands” SOAP messages. 
   Network 
   SOAP communications between requesting application  202  and WSA  204  may be made over network  220 . Network  220  may be implemented by any medium or mechanism that provides for the exchange of data between various nodes in network  220 . Examples of such a network include, without limitation, a network such as a Local Area Network (LAN), Wide Area Network (WAN), Ethernet or the Internet, or one or more terrestrial, satellite, or wireless links. Network  220  may include a combination of networks such as those described. Network  220  may transmit data according to Transmission Control Protocol (TCP) and Internet Protocol (IP). 
   Web Services Application 
   Web services application (WSA)  204  and WSA  206  are modules that provide services and that rely on Web Services protocols and technologies, such as those protocols supported by WSPM  210 . WSA  204  and WSA  206  may also rely on the routines provided by SSM  208  if the respective applications are not configured to analyze SOAP messages. 
   In one embodiment, WSA  204  and WSA  206  have a socket where the respective applications “listen” for SOAP requests. WSA  204  and WSA  206  may be configured to listen for SOAP requests at the same socket or at different sockets. 
   Soap SDK Module 
   SOAP (Simple Object Access Protocol) is a XML-based messaging protocol used to encode the information in Web service request and response messages before sending them over a network. SOAP messages are independent of any operating system or protocol and may be transported using a variety of Internet protocols, including SMTP, MIME, and typically HTTP. 
   The Web Services Description Language (WSDL) is an XML format published for describing Web services. WSDL describes the public interface to a particular Web service. WSDL is an XML-based service description on how to communicate using the Web service. A WSDL file describes the protocol bindings and message formats required to interact with the Web services listed in its directory. The supported operations and messages are described abstractly, and then bound to a concrete network protocol and message format. 
   WSDL is often used in combination with SOAP and XML Schema to provide Web services over the internet. A client program (e.g. requesting application  202 ) connecting to a Web service (e.g. WSA  204 ) may read the WSDL file corresponding to the Web service and determine what functions the Web service supports. Any special datatypes used are embedded in the WSDL file in the form of XML Schema. The client program can then use SOAP to invoke one of the functions listed in the WSDL file. 
   According to an embodiment, SOAP SDK module (SSM)  208  is a shared library of library routines that implement one or more functions defined by SOAP and/or WSDL. SOAP  222  comprises one or more library routines corresponding to SOAP. The one or more library routines corresponding to SOAP may be associated with the SOAP 1.2 standard or any other version of SOAP. Similarly, WSDL  224  comprises one or more library routines corresponding to WSDL. The one or more library routines corresponding to WSDL may be associated with the WSDL 1.2 standard or any other version of WSDL. SSM  208  may comprise library routines corresponding to older versions of SOAP and WSDL so that requesting applications  202  may operate under the older versions. 
   A WSA may invoke library routines provided by SOAP  222  to 1) generate a SOAP message and/or 2) parse a SOAP request that the WSA has received. A WSA may also invoke library routines provided by WSDL  224  to package WSDL documents to send to requesting application  202 . WSDL  224  is used to analyze a given WSDL document and generate stubs and skeletons during the development phase. At runtime, WSDL  224  is used to map incoming requests to the corresponding functions “inside” WSA  204  or  206 . WSDL  224  is not required to generate the WSDL document for the outside because the document is typically a simple text file. 
   In one embodiment, SSM  208  is implemented as a set of static or dynamic library routines which WSA  204  and WSA  206  may each load into their respective memories. Therefore, WSA  204  and WSA  206  may each invoke different copies of the same library routine. In another embodiment, WSA  204  and WSA  206  invoke a library routine using an API associated with SSM  208 . The API defines an interface by which the associated WSA invokes one or more functions on SSM  208 . In this case, SSM  208  implements the functions specified in the library routine and returns the results to the WSA that invoked the library routine. 
   If the WSA invokes a SOAP library routine, then the structure of the SOAP request is analyzed (either locally, in the case of loading the library routine into memory, or by SSM  208 , in the case of SSM  208  implementing the function(s) specified in the library routine). If the structure of the SOAP request is valid, then the one or more portions of the SOAP request are identified. Each portion specifies a particular Web Services specification. Results from executing the SOAP library routine may comprise data structures that contain pointers to each portion with an identifier that indicates the Web Services specification or the name of the namespace of the Web Services specification. 
   Each Web Services specification has an associated namespace. The namespace identifies a particular Web Services specification. Each version of a particular Web Services specification is associated with a different namespace. Therefore, WSDL 1.1 and WSDL 1.2 are associated with different namespaces. 
   Web Services Protocol Module 
   Web Services protocol module (WSPM)  210  functions as a shared library of library routines that each implement one or more functions defined by one or more Web Services specifications. A WSA knows which library routine(s) to invoke based on the results of invoking one or more SOAP library routines to analyze the SOAP request. 
   In one embodiment, WSPM  210  may be implemented as a set of static or dynamic library routines which WSA  204  and WSA  206  may each load separately into memory. Therefore, WSA  204  and WSA  206  may each invoke different copies of the same library routine. In another embodiment, WSA  204  and WSA  206  invoke a library routine using an API associated with WSPM  210 . The API defines an interface by which the associated WSA invokes one or more functions on WSPM  210 . In this case, WSPM  210  implements the functions specified in the library routine and returns the results to the WSA that invoked the library routine. 
   According to an embodiment, WSPM  210  comprises one or more library routines corresponding to at least one Web Services specification. WSPM  210  may be configured to comprise library routines that correspond to multiple Web Services specifications and multiple versions of one or more Web Services specifications. 
   Web Services specifications include standards for messaging, security, transactions, and policy. Web Services messaging specifications include, without limitation, WS-Addressing, WS-Eventing, and WS-Transfer. WS-Security is a well-known security specification. Web Services transaction specifications include, without limitation, WS-Coordination and WS-BusinessActivity. Web Services metadata specifications include, without limitation, WSDL, WS-MetadataExchange, and WS-Policy. Many other specifications are currently in the proposal phase and will eventually become W3C standards. 
   Multiple WSAs may invoke the library routines defined in WSPM  210 . Therefore, multiple WSAs may benefit from one WSPM  210  without a WSA developer having to know many details about the Web Services specifications implemented on WSPM  210 . 
   Abstract API 
   According to an embodiment, WSA  204  and WSA  206  may use an abstract API, such as abstract API  214  for WSA  204  and abstract API  216  for WSA  206 , in order to generate device-specific requests. The abstract API defines an interface by which the associated WSA invokes one or more functions on the MFP. Therefore, according to this embodiment, a developer of WSA  204  and/or WSA  206  is not required to know the underlying complexities of the target platform, but only of the new service that the developer aims to provide. 
   Abstract API Implementation 
   If an abstract API has been defined for a WSA, then an implementation of the abstract API for a specific platform must be defined. For example, an abstract API implementation  244  is defined for abstract API  214  on a platform alpha  240 . Similarly, an abstract API implementation  266  is defined for abstract API  216  on a platform gamma  260 . A corresponding abstract API implementation defines the functions specified in a device-specific request and implemented on the MFP. With this architecture, only the implementer of the abstract API needs to have knowledge of the target platform, whereas the developer of the WSA is not so required. 
   Example  
     FIG. 3  illustrates an example of how a SOAP request for a printing service may be processed, according to an embodiment of the invention. Initially, requesting application  202  receives a platform-specific request from a word processing application (not shown) to print an electronic document. The request indicates that the electronic document should be encrypted and that the user of the word processing application wants to be notified when the print job is fully executed (i.e. the entire electronic document is printed). 
   At step  1 , requesting application  202  may initially send a SOAP request for the WSDL file associated with WSA  204  that handles print requests. WSA  204  executes on a MFP that provides one or more services in addition to a printing service, such as a faxing service, a scanning service, and an archiving service. Therefore, the MFP includes at least a print process for processing print data and causing a printed version of an electronic document reflected in the print data to be generated. 
   At step  2 , WSA  204  sends the WSDL file to requesting application  202  over network  220 . The WSDL file lists the functions that WSA  204  supports. If WSA  204  does not include functionality to analyze SOAP messages, then WSA  204  may forward the SOAP request to SSM  208 . SSM  208  then may extract the details of the request and send them to WSA  204  (step  3 ). 
   If the WSDL file indicates that WSA  204  and its associated MFP does not support the functionality that the requesting process requires (e.g. encryption), then requesting application may attempt to discover another WSA that supports the requested functionality. 
   If WSA  204  and the MFP support the requested functionality, then requesting application  202  converts the platform-specific request into a SOAP request (e.g. using the WSDL file) and sends the SOAP request, over network  220 , to WSA  204  (step  3 ). 
   The header of the SOAP request comprises one or more portions that each correspond to a particular Web Services specification. According to this example, the header of the SOAP request includes a portion that corresponds to the WS-Eventing specification (for notifying requesting application  202  when the print job is fully executed) and another portion that conforms to the WS-Security specification (for specifying the encryption process used to encrypt the electronic document). The body of the SOAP request comprises the encrypted electronic document. 
   WSA  204  receives the SOAP request and invokes a SOAP library routine provided by SSM  208  (step  4 ) (e.g. by using a SOAP API associated with WSA  204 ) if WSA  204  does not already include an implementation of the appropriate SOAP specification to which a portion of the SOAP request conforms. SSM  208  analyzes the structure of the SOAP request. The results from the SOAP library routine include identifiers that identify WS-Security and WS-Eventing as the Web Services specifications specified in the SOAP request. The results are returned to WSA  204  (step  5 ). 
   At step  6 , based on the results from the SOAP library routine, WSA  204  invokes at least one library routine defined in WSPM  210 . In this example, WSA  204  invokes one or more library routines, corresponding to WS-Security, that implement decryption of the print data in the SOAP request. By invoking the library routine, the security mechanism is determined, the key is identified, and the electronic document in the SOAP request is decrypted. 
   After WS-Security  238  decrypts the electronic document, WSPM  210  returns the decrypted electronic document to WSA  204  (step  7 ). At step  8 , WSA  204  uses abstract API  214  to generate a device-specific print function call and transmit the print function call to the target platform (e.g., platform alpha  240 ). The corresponding abstract API implementation (e.g., implementation  244 ) implements the print function call. However, after the decryption, if WSA  204  determines that the electronic document is in a format that platform alpha  240  does not “understand”, then the print job may be aborted. 
   When the print job is fully executed, platform alpha  240  invokes a callback to WSA  204  (e.g., via abstract implementation  244 ) notifying WSA  204  of this event (step  10 ). WSA  204  invokes one or more library routines corresponding to WS-Eventing  236 . The results from executing these library routines is used when invoking one or more SOAP library routines corresponding to SOAP  222  in order to generate a SOAP message to application  202  if it has previously requested to receive such notifications, through a different SOAP message. The SOAP response indicates that the print job is fully executed. 
   If there are applications that have previously registered to be notified of events, then eventing notifications are sent based on callbacks from the corresponding abstract API (e.g., abstract API  244 ). If no application has registered, then an eventing message is not sent. 
   If the original SOAP request comprises of a portion that conforms to a Web Services specification that is not implemented by library routines defined in WSPM  210 , then WSA  204  may still attempt to execute the SOAP request using the other Web Services specifications indicated in the SOAP request. In this way, WSA  204  may service some SOAP requests that WSA  204  would otherwise abort or ignore. 
   However, a SOAP request from requesting application  202  may indicate a certain policy (e.g. according to WS-Policy) that each portion in the SOAP request corresponding to a Web Services specification must be implemented. In such a case where a SOAP request indicates the aforementioned policy, if WSPM  210  does not support a Web Services specification specified in the SOAP request, then the entire SOAP request may be discarded and an error message may be sent to requesting application  202 . 
   Implementation Mechanisms 
   The approach described herein for providing Web Services protocol to Web service applications may be implemented on any type of computing platform or architecture.  FIG. 4  is a block diagram that illustrates a computer system  400  upon which an embodiment of the invention may be implemented. Computer system  400  includes a bus  402  or other communication mechanism for communicating information, and a processor  404  coupled with bus  402  for processing information. Computer system  400  also includes a main memory  406 , such as a random access memory (RAM) or other dynamic storage device, coupled to bus  402  for storing information and instructions to be executed by processor  404 . Main memory  406  also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor  404 . Computer system  400  further includes a read only memory (ROM)  408  or other static storage device coupled to bus  402  for storing static information and instructions for processor  404 . A storage device  410 , such as a magnetic disk or optical disk, is provided and coupled to bus  402  for storing information and instructions. 
   Computer system  400  may be coupled via bus  402  to a display  412 , such as a cathode ray tube (CRT), for displaying information to a computer user. An input device  414 , including alphanumeric and other keys, is coupled to bus  402  for communicating information and command selections to processor  404 . Another type of user input device is cursor control  416 , such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor  404  and for controlling cursor movement on display  412 . This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. 
   The invention is related to the use of computer system  400  for implementing the techniques described herein. According to one embodiment of the invention, those techniques are performed by computer system  400  in response to processor  404  executing one or more sequences of one or more instructions contained in main memory  406 . Such instructions may be read into main memory  406  from another machine-readable medium, such as storage device  410 . Execution of the sequences of instructions contained in main memory  406  causes processor  404  to perform the process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. 
   The term “machine-readable medium” as used herein refers to any medium that participates in providing data that causes a machine to operation in a specific fashion. In an embodiment implemented using computer system  400 , various machine-readable media are involved, for example, in providing instructions to processor  404  for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device  410 . Volatile media includes dynamic memory, such as main memory  406 . Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus  402 . Transmission media can also take the form of acoustic or light waves, such as those generated during radio-wave and infra-red data communications. 
   Common forms of machine-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punchcards, papertape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. 
   Various forms of machine-readable media may be involved in carrying one or more sequences of one or more instructions to processor  404  for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system  400  can receive the data on the telephone line and use an infra-red transmitter to convert the data to an infra-red signal. An infra-red detector can receive the data carried in the infra-red signal and appropriate circuitry can place the data on bus  402 . Bus  402  carries the data to main memory  406 , from which processor  404  retrieves and executes the instructions. The instructions received by main memory  406  may optionally be stored on storage device  410  either before or after execution by processor  404 . 
   Computer system  400  also includes a communication interface  418  coupled to bus  402 . Communication interface  418  provides a two-way data communication coupling to a network link  420  that is connected to a local network  422 . For example, communication interface  418  may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface  418  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface  418  sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. 
   Network link  420  typically provides data communication through one or more networks to other data devices. For example, network link  420  may provide a connection through local network  422  to a host computer  424  or to data equipment operated by an Internet Service Provider (ISP)  426 . ISP  426  in turn provides data communication services through the world wide packet data communication network now commonly referred to as the “Internet”  428 . Local network  422  and Internet  428  both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link  420  and through communication interface  418 , which carry the digital data to and from computer system  400 , are exemplary forms of carrier waves transporting the information. 
   Computer system  400  can send messages and receive data, including program code, through the network(s), network link  420  and communication interface  418 . In the Internet example, a server  430  might transmit a requested code for an application program through Internet  428 , ISP  426 , local network  422  and communication interface  418 . 
   The received code may be executed by processor  404  as it is received, and/or stored in storage device  410 , or other non-volatile storage for later execution. In this manner, computer system  400  may obtain application code in the form of a carrier wave. 
   In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.