Modeling SOA can be a challenge. Good news, the folks at OMG have been working on it...
"It's an extension of the UML, the Unified Modeling Language, and it contains modeling constructs for things like contracts and service and providers and consumers, all things that you would expect if you were going to do the architectural delivery for a SOA-based project,"
The specification will be published as a UML profile, meaning it can be used in any UML modeling tool. It can be extended and built upon, Harrison said. Tools vendors are expected to incorporate it in their products,
A little more at Infoworld.