Are the reasons like in normal multi-module application programming - so a client can just use the interface without having to worry about implementation details?
Note that I am talking about WSDI/UDDI/SOAP and not normal application interfaces.
A WSDL has an abstract part and a concrete part and they are separate as to allow the reuse of these definitions. The same contract can be bound to many concrete network protocols and message formats.
This reuse of definitions, in the context of UDDI means one interface, multiple implementations.
One of the idea with UDDI was that needed web services could be discovered at runtime. And you can go inside the registry and look for implementations of a certain WSDL contract:
Beyond the Cookbook: Interfaces and Implementations
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If three different companies have implemented the same WSDL file and a piece of client software has created the proxy/stub code for that WSDL interface, then the client software can communicate with all three of those implementations with the same codebase
[...]
At least that was the theory. In practice it turned out another way.
