Using WSML and WSDL
To expose a COM object using the SOAP toolkit, it's necessary to provide two different XML documents that describe the SOAP service to be provided, as well as the concrete COM object methods that must be invoked. The close relationship between the WSML and WSDL files can be confusing at times, but the basic purpose of each is easy to understand.
The WSDL document exposes a set of generic SOAP services, bindings, ports, and messages for use by any SOAP client. It's a W3C-endorsed standard that's being promoted by Microsoft and other vendors as a standard way to expose programmatic services on the web. It doesn't contain any Microsoft-specific or COM-specific information.
However, these generic declarations don't provide sufficient information for the SOAP server to actually process a request. To do this in a Windows framework, there must be some way to associate an actual COM object and specific method with each inbound SOAP message. This is the purpose of the WSML file. It defines which COM objects will service which incoming messages. It links the message elements from a SOAP request to specific method parameters in the requested COM object. Together, the WSDL and WSML files allow end-to-end processing of SOAP requests.