XML Schema is commonly used in technical documents, including Internet RFCs, to express the syntax for XML in various documents and protocol messages. It's also the basis for SOAP, WSDL, and UDDI.
I have felt for a long time that XML schema is ugly and useless. It's ugly because it is so difficult to read. Most published documents, even Word documents, don't publish the XML Schema with syntax highlighting, which would certainly help. But if it's hard to read, at least it's machine readable, right? True, but it's rare for anyone to use validation tools with a published XML Schema. The published schema is often just for human consumption.
Now, however, I feel that my feelings have been affirmed. The following is quoted from an email by Tim Bray:
Many people in the XML community - I hesitate to say consensus, but would claim at least a plurality - feel that [Relax NG] is substantially technically superior to both DTDs and W3C XML Schemas. ... W3C XML Schema is a profoundly bad design which exhibits very poor comprehensibility and interoperability.
So, at least in Tim's opinion, Relax NG should be the way forward.
Read Tim's complete email in the archive. It's a short but interesting read.
Posted by Doug Sauder at November 7, 2005 08:34 PM