posted 6 years ago
I think that Frank Cohen described it very nicely. It's a bit old but seems to explain the issue well - Understanding web service interoperability. Frank says -
Stepping onto the new web services island one might think "Oh brave new world that has such wonders." Then the reality of web services sets-in. Dozens of platform providers, independent software vendors, and utility software developers have implemented web services protocols (SOAP, WSDL, and UDDI) in their products. While the protocols are now nearly two years old and working drafts of the next specifications (SOAP 1.2 for example) are in the works, developers have had to interpreted the meaning in parts of the specifications. Interpretation allows interoperability problems to seep into SOAP-based web services.
Web service interoperability goals are to provide seamless and automatic connections from one software application to another. SOAP, WSDL, and UDDI protocols define a self-describing way to discover and call a method in a software application -- regardless of location or platform. Data is marshaled into XML request and response documents and moved between software packages using HTTP or message-based protocols. Interoperability problems creep in at the discovery, definition, and request/response mechanisms.