What are the fundamentals?  I'm getting ready to write a new web service
and I'd like to have the ability to add interfaces as they change to
support 'COM-like' backwards compatibility.

Clients for this web service will be using SOAP and auto-generating SOAP
headers from Visual Studio .Net.

I'm also interested in having multiple different interfaces in the same
web service as well.

Last but not least, what is the best book in your opinion about how to
write web services (preferably in C#, but that's not all important)?

    WTH