Principles of Web Service Design

John Evdemon just published 2
articles on the principles of web service design.

The first one is titled Principles
of Service Design: Service Patterns and Anti-Patterns and in my opinion
should be required reading for anyone who is new to web service development.
Specifically, anyone new to building web services should focus on his
explanation of the 4 tenets of service orientation, and the anti-patterns - this
is good stuff - but if you've been staying up to date on web service
architecture and development, you won't read much you haven't read/heard before.
If you think you're pretty up-to-speed on web services, just breeze through
those parts and check out the patterns - they tend to be more specialized.

The second article is titled Principles
of Service Design: Service Versioning. This article was of particular
intereste to me since I've done quite a lot of thinking about the right approach
to versioning web services. If you haven't thought much about how you're going
to version your services, definitely check out this article. John does a good
job of getting you up to speed on the issues quickly - this is a difficult
problem to solve in an elegant way.

This is something you might not pick up on while reading the article. Notice
how John does not consider the use of strings or XML nodes an option for message
versioning. He doesn't consider this because it's not recommended. Coupling is
not loose or tight - there are varying degrees of it. Typing web service
messages as strings is too loose, but not providing an extension mechanism or
open content model is too tight. John is recommending a nice balance.

I didn't expect the article to effectively say, "here is how you should
version your web services," which it doesn't, but, I like John's approach. He
effectively says, "here are the issues and here are some principles that should
guide your decision making." This is about the most you can ask for at this
point. No one in the entire industry has come up with a definitive, elegant
mechanism that addresses versioning for all types of services. I would like to
see that happen someday. I'm currently working on some tooling that may result
in great strides to this end. More later ;-)