Versioning XML Vocabularies

Orchard, D
Orchard, D
Web Paper,
Citations range: 
1 - 9

XML is designed for the creation of languages based upon self-describing markup. The inevitable evolution of these languages is called versioning. Versioning means adding, deleting, or changing parts of the language. Making versioning work in practice is one of the most difficult problems in computing, with a long history of failed attempts. Arguably one reason why the Web rose dramatically in popularity is because evolution and versioning were built into HTML and HTTP headers, each of which provides explict extensibility points and rules for understanding extensions that enabled their decentralized extension and versioning.
XML Namespaces provide an ideal mechanism for identifying versions of languages, and all XML schema languages -- such as W3C XML Schema -- provide for controlled extensibility.
This article describes techniques to achieve more effective loose coupling between systems by increasing the possibility for backwards- and forwards-compatible changes to occur when related systems evolve. These techniques are designed for compatible changes with or without schema propagation. A number of rules are described for versioning XML vocabularies, making use of XML Namespaces and XML Schema constructs. It includes rules for working with languages that provide an extensible container model, notably SOAP. The collective set of rules is called the \"Must Ignore\" pattern of extensibility. Strangely, the \"Must Ignore\" pattern for HTML tags and HTTP headers that significantly helped their adoption has not been widely adopted by XML practitioners. This article aims to rectify that situation for current Schema validation environments. Follow-on material will explore innovative relaxed schema validation environments.