Custom Datatypes in RELAX NG Using Java
By toddfast on Dec 03, 2004
To give you an idea of what this article is about, several RELAX NG schema validators (like Sun's Multischema Validator, or MSV) let you plug in custom datatype validation using simple Java constructs. This capability can be used to go (way) beyond traditional document validation, even to the extent of verifying that a piece of XML data fulfills requirements above and beyond its syntax. For example, it would be possible to verify that a document contains a valid credit card number (and maybe even post a fund reserve) with an online clearinghouse during the validation phase, rather then relying on the application layer to do this sort of validation at a later stage. Such semantic validation is extraordinarily powerful.