This part of the book answers the question of how to go about discovering all the important metadata (the explicit service description information) that supports service orientation. The figure that follows shows where metadata falls in the Web services stack.
This part presents two approaches for discovering metadata: via a centralized registry (UDDI) or by distributed discovery (Metadata Exchange). UDDI, which is discussed in Chapter 8, "Universal Description, Discovery, and Integration," provides a centralized registry of metadata that can reference all kinds of information, including WSDL documents, policies, and others, and offers several powerful and flexible techniques for querying the registry.
WS-Metadata Exchange, which is discussed in Chapter 9, "Web Services Metadata Exchange," is a protocol for querying a Web service endpoint for its own metadata. This simple protocol allows an application to ask any service endpoint for its WSDL document, for its policies, for any schemas, or for any other kind of metadata.
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