To understand the current thoughts of the standard community on this issue, here are a few useful blogs and articles you don’t want to miss:
 Extensibility, XML Vocabularies, and XML Schema, by David Orchard
David did a good job defining what’s backward and forward compatibility. In addition, the article provides a few very good advise about how to use extensibility to accomodate compatible changes, and how to use various version identification strategies.
To complement this article, you should also read [1.1]Designing Extensible, Versionable XML Formats By Dare Obasanjo [1.2]2 XML.com articles on XML Extensibility and Versioning, David’s blog explaining the common points and differences between  and [1.1]
 Loose coupling and WSDL versioning, a blog by Chris Ferris
Does any change to a WSDL has to result in a new WSDL namespace? In this blog, Chris shows two ways to avoid that
- Use XSD extensibility for the message to be exchanged, or
- Use WSDL extensibility for adding new operations
 Versioning Service Data using WSDL Application Data Feature, a blog by David Orchard
If you don’t have a chance to design your schema as suggested by  and , you may want to check out the WSDL2.0 AD feature.