RE: [xml-dev] A Systematic Approach to using Simple XMLVocabularies to Implement Large (Complex) Systems

> Has anyone tried to express the validity or  'life' of information?

Yes, there is a lively research stream under the name "temporal databases",
and many more-or-less ad-hoc approaches in fields such as medical records
and genealogy.

Michael Kay
http://www.saxonica.com/