Taking XML Validation to the Next Level: Introducing CAM

alidating an XML document entails confirming that the document is both well-formed and conforms to a specific set of rules specified with a Document Type Definition (DTD), an XML Schema, or—as introduced in this article—a CAM template. DTD was the earliest specification. DTDs provided useful but limited capabilities, letting you validate XML document structure but very little in the way of semantics. Next came XML Schema, which offered more flexibility and capability, improved support for structure, and good (but not great) support for semantics. Schematron, RelaxNG, and others have attempted to improve the semantic support, but none have caught on in a big way. Now a new—really new—technology called Content Assembly Mechanism (CAM) is being developed under the aegis of OASIS, a well-respected standards body.

CAM is more than just another schema language, though. It was designed to better meet the needs of business exchange requirements and interoperability. CAM provides a powerful mechanism for validating XML both structurally and semantically, in a concise, easy-to-use, easy-to-maintain format. It provides a context mechanism—a way to dynamically adjust what should be considered a valid XML instance based upon other parts of the XML itself or external parameters.