SOA Tenets?

1. Boundaries are explicit
2. Services are Autonomous
3. Services share Schema and Contract, not Class
4. Compatibility is based upon Policy

Of these Microsoft tenets of WCF the 2nd seems the most documented.

Another way of looking at is:

1a. Assume an idiot will use your service and design it accordingly.
2a. Try to design your Service not to depend on other Services that much.
2b. Your Service will change over time and break compatability, stop kidding yourself that it won't.
3. Services tend to pass data around.
4. Despite popular belief, you *can* have too much metadata so don't be disappointed when people ignore it.

Thanks to Adam Magee for linking me to David Ing's blog entry

You gotta like a guy who presents "SOAP: It wasn't Simple, we didn't Access Objects, and it's not a Protocol."