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Carnage4Life: Open Letter To Keith Ballinger and Simon Fell. Dare notes that Simon use of words weren't precise. Within minutes, the precision of Dare's own words were questioned.
In any case, it seems clear to me (particularly as Simon gave a full example) that Simon was referring to the namespace name, which is determined by the qualified name, either explicitly based on the namespace prefix or implicitly based on the default namespace.
What's more unfortunate is that the small gaffe obscured Keith's real question, which was how one determines the correct message definition associated with a given message. The answer is that you can't. A message may not have a definition. It may also conform to multiple definitions.
What Object Does SOAP Access? covers this topic from another (non-WSDL) perspective.