ISO Namespace Validation Dispatching Language (NVDL) is a little language for taking an XML documents, sectioning it off into single namespace sections, attaching or detatching these sections in various ways, and then sending the resulting sections to the appropriate validation scripts.

NVDL solves several problems that come up with namespaces, and as with DSRL takes a very different approach than XSD takes (not saying one is better or worse: they have different capabilities and therefore may even be used together). One of these problems is the problem that often the official schema has a wildcard to say “at this point you can put any element”, but you really want to limit this to your own elements only and you don’t want to edit the official schemas (and thereby create versioning and configuration issues).

Another of these issues can be found in ODF. It allows foreign elements anywhere, and in order to validate against the schemas you have to strip these out. However, this does not mean just remove the foreign element and their children, you have to leave the non-foreign descendents in place.

Now this is something that W3C XSD cannot really handle well. You can have a wildcard to allow foreign elements, and process them laxly so that when you come to an ODF namespace you start validating, but you don’t have the capability of validating that these elements are correct against the content model you want on the parent of the wildcard. You lose synch.

Read the complete article by Rick Jelliffe.