"WSDL" doesn't validate anything. "WSDL" is an XML-based language for
describing web services.

If you mean, "doesn't ASP.NET validate messages against the schemas in a
WSDL describing this web service", then the answer is, "no", and "what made
you think that it did validate"?

First of all, you say that your web service "implements a WSDL". This sounds
like you used WSDL.EXE to create a stub class or interface, and that you
then wrote code which implemented that class or interface. In this case, the
WSDL is out of the picture. WSDL.EXE put attributes on the class or
interface and its methods, and perhaps on types which it generated from the
WSDL file. ASP.NET interacts with those attributes at run time to do things
like serialize and deserialze messages.

Note that ASP.NET is not interacting with the WSDL file. In fact, you won't
find the path to the WSDL file anywhere in the generated code.

Note further that none of these attributes says anything about validation,
or about what to do in the case of a validation error.

If you'd like to add validation, see the excellent article, "Extend the
ASP.NET WebMethod Framework by Adding XML Schema Validation" at
http://msdn.microsoft.com/msdnmag/issues/03/07/xmlschemavalidation/default.aspx. I
have created an implementation of this code for my own web service, and find
it extremely useful, not only for validating incoming messages, but also for
making sure that my web service generates valid output!

John