Compatibility of XML Language Versions

Individual organisations as well as industry consortia are currently defining application and domain-specific languages using the eXtended Markup Language (XML) standard of the World Wide Web Consortium (W3C). This trend introduces new challenges for version and configuration management. We show that configuration management for XML languages is considerably more complicated for an XML Schema or DTD than it is for traditional software engineering artifacts. In addition to internal consistency of the language definition, also consistency between the language and its instance XML documents needs to be preserved when evolving the language definition. We propose a definition for compatibility between versions of XML languages that takes this additional need into account. Compatibility between XML languages in general is undecidable. We argue that the problem can become tractable using heuristic methods if the two languages are related in a version history. We propose to evaluate the method by using different versions of the Financial products Markup Language (FpML) in whose definition we participate.