We are often asked to define WSDL- and schema design guidelines (contract-first) for clients. We have found a core set of guidelines that seem to work well for clients using XML_binding. The core challenge is to find a portable and reasonably useful approach to controlled evolution, supporting backwards- and forwards compatibility across service consumers and producers bound (via JAX-B or .Net binding technologies). We’ve seen the chosen approach being used fairly broadly, among others in several oasis specifications (as an example: WS-Topic in WS-Notification), but never really found a good, authoritative point of reference. Until i found this excellent document by w3c. It outlines the problem, defines a number of versioning strategies - each with an identification, and finally lists examples of standards bodies that apply the different strategies. The strategy we are endorsing is number 2.5.