WebMethods make the development of XML Web Services easier by encapsulating a good deal of functionality, but there is still a lot of underlying XML processing that you have to be responsible for. For example, WebMethods do not validate messages against the implied schema. Because they are not validated, the response that's returned can result in unintended consequences. To address this, the authors extend the WebMethod framework by adding XML Schema validation through a custom SoapExtension class.
Aaron Skonnard and Dan Sullivan
MSDN Magazine July 2003
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