Error validating check constraint
This paper provides an introduction to Schematron; an innovative XML validation language developed by Rick Jelliffe.This innovation stems from selecting an alternative approach to validation than existing schema languages: Schematron uses a tree pattern based paradigm, rather than the regular grammars used in DTDs and XML schemas.Tree patterns are the schema paradigm underpinning Schematron as a validation language.
Assertions are therefore the mechanism for placing constraints on the relationships between nodes in a graph (elements and attributes in an XML document).
There is no enforcement that an IDREF must point to an ID on a particular element type, simply that is must point to an existing ID, and further that all IDs must be unique.
Having highlighted the fact that the existing schema paradigm can only express constraints among data items in terms of the child and sibling axes, it is natural to consider whether an alternate paradigm might allow a schema author to exploit these additional relationships to define additional types of constraint amongst document elements.
The general intent behind this paper is to furnish the reader with a broad overview of both Schematron and its approach to validation.
It does not provide a detailed tutorial of the language, although all major elements are discussed, and assumes that the reader is already familiar with XPath, XSLT, and XML DTDs.