Some References on Extensible XML Schema Design

This topic came up in a WCF training session (i.e. ObjectSharp's WCF course) I am currently delivering so I wanted to post a few references on the subject here:

The first is "Designing Extensible, Versionable XML Formats" by Dare Obasanjo

The second, slightly more academic treatment is "Extensibility, XML Vocabularies, and XML Schema", by David Orchard, an extensibility guru who has much to say on the topic:

And then finally a series of writings by Tim Ewald which are chock full of extremely powerful Versioning advice:

First his "Services and the Versioning Problem" article in the MS Architecture Journal:

And then a series of blog entries: