Transforming schemas

The traditional approach to transforming XML documents is a three-step pipeline: validate, transform, validate. The SGML feature called architectural forms combined enhancements to DTDs with annotations in source documents to allow a valid SGML document to be automatically transformed into another SGML document valid against a different DTD. This permitted document creators to conform to a general document architecture without having to constrain their own documents to every detail of a specific schema. In the XML world, however, the emphasis has been on the creation of comprehensive schemas rather than easy transformation, and the ideas behind architectural forms have mostly been lost. This paper attempts to explain how to restore those ideas to XML practice.