Norm Walsh has released three experimental schemas for the DocBook 4 technical documentation XML application: using not only W3C XML Schema, but also RELAX and James Clark's new entrant, TREX.
The schemas are available from the OASIS DocBook site:
Walsh writes that he produced the TREX schema by derivation from the RELAX version. This, among other early uses of TREX, signals an approbation for James Clark's schema language among the XML community. Several months ago XML developers were faced with one monolithic solution to the schema problem, now they have a choice of three tools from which to pick the best for the job in hand.