XML Registries for P2P


In Chapter 11 we discussed the three Web services stacks: the wire stack, the description stack, and the discovery stack. As this chapter is dedicated to XML registries, we will therefore be covering the discovery stack here. Let's first establish a case for using XML registries in P2P applications.

Recall that Web services do not essentially reside over the Internet. They may reside on a network, on an intranet, or even on a P2P network. XML registries will act as the discovery stack, irrespective of the type of network that hosts the Web services being discovered.

Therefore, if we try to define the role of XML registries over P2P networks, we can say that XML registries play the same role over P2P networks that they play over the client-server model of the conventional Internet. Web services residing over P2P networks can be published on XML registries, and users looking for those services will find them in the same way.

To understand exactly how to publish P2P-based Web services on a UDDI registry, recall the WSDL and UDDI sections of Chapter 11. The WSDL section describes the roles of portType, binding, and port elements in WSDL authoring. These three elements of a WSDL file together achieve decoupling between abstract Web service definitions and their concrete correspondence to actual protocols. This decoupling framework assures that a Web service is independent of the wire-level protocol (such as SOAP over HTTP, an example in Chapter 11) and the address used for hosting. As a practical example, Chapter 20, "Using SOAP with P2P," demonstrates how to use SOAP over P2P instead of SOAP over HTTP as the Web services interoperability wire stack.

The tModel-related discussion of the UDDI section in Chapter 11 builds on this idea of decoupling. A UDDI tModel provides the abstract definitions of a Web service interface, which can be referred to by any implementation or instance of that particular service. For instance, a P2P Web service publisher will refer to the corresponding tModel for the abstractions, and provide the remaining concrete part of the definitions.

The last section of this chapter, "Accessing Web Services," explains why, when, and how to use the different Web service-related technologies (XML, SOAP, WSDL, UDDI, and so on) in P2P applications.



JavaT P2P Unleashed
JavaT P2P Unleashed
ISBN: N/A
EAN: N/A
Year: 2002
Pages: 209

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