The XML-dev mailing list has recently seen a lively and informed debate as to the value of a single schema language and centralized schema repositories.

The debate was initiated by Matthew Gertner, who announced that he had posted a short "XML Rant" arguing for a standard schema language and schema repository.

Rick Jelliffe responded that while he agreed there ought to be a standard schema discovery mechanism, there should not be a standard schema language: "Every schema language is built on a zillion trade-offs. The best we can hope for is that a schema language will be wonderful on some major application domain and not entirely useless generally."

In other parts of the debate, attention focused on schema repositories, and whether the goal of a unified repository was possible. Tim Bray commented: "I share the doubt that a grand unified schema repository will be tractable to build & maintain. I also am enthusiasm-challenged because in my (lengthy) experience with XML and its ancestors, I have only ever seen machine-readable schemas put to use in one application: namely the use of DTDs in hand-authoring XML documents. "

Don Park shared the scepticism, saying "My opinion on unified schema repository is that it won't happen while everyone is interested in it because expectation leads to escalating hype and politics." He went on to share a vision of a schema bridge service which would convert between schema languages, and an ultimate "Unified Schema Bridge Registry".

The whole thread, spanning several days in the archives, is worth reading for an excellent tour of the issues involved in schemas, and their description and discovery.