The official schema namespace for WSDL 1.1 is http://schemas.xmlsoap.org/wsdl/. But, and here is the fun part, the schema for that namespace given in the official W3C WSDL 1.1 note and the schema for that namespace given at the actual XML namespace URL are different. But wait, it gets better. Not only are the two schemas different, they aren't even compatible with each other! I'll give the gory details below but the bottom line is that there exist two incompatible versions of the WSDL 1.1 schema, one in the W3C note and one at the actual XML namespace URL which use the same XML namespace and the same element names. Just to add to the fun the WS-I has officially approved the schema at the actual namespace URL in contradiction to the schema in the W3C WSDL 1.1 note. So now implementers get to pick which industry body they favor since they have competing, incompatible, definitions for the WSDL 1.1 schema. I suppose errors like this make it more understandable why versioning in Web Services is such a disaster.