I was going to comment on Clemens Vasters' article on Staying sane in an XML Web Services World , but Sam Ruby beat me to it. Clemens says:

In XML, the interface is XML Schema. No, it's a way to help expressing semantics.

I disagree, I like what Phil Windley says on this:

All these XML standard definitions point out the big flaw in everyone's wishful thinking concerning XML. To do what people want it to do, XML would have to be able to convey semantics. Because it's just a CFG, it can't. So, the semantics have to live somewhere else: the standard and what people understand about it. The problem is that as soon as you have a standard syntax, you've negated much of the benefit of on-the-fly parsing.

Furthermore, Clemens assumes that XML Schema is the only way to communicate a contract, but my understanding is that WSDL does not have this limitation. I'd also like to suggest that Clemens' rule #3 is tacitly encouraging people to use .NET DataSets, which I understand to be a first-class interop-killer. And if you don't interop, why were you doing SOAP again?