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Differences between NVDL and W3C XML Schema Approach to Compound Document Validation

W3C XML Schema approach	NVDL approach
All possible usages of vocabulary has to be known in advance.	Vocabularies can be combined on demand.
“Early binding” between namespaces	“Late binding” between namespaces
“Tightly” coupled schemas	“Loosely” coupled schemas
Driven by authors of “base” vocabularies and their schemas.	Driven by users and needs of their compound documents.

Best practice: Create single namespace schemas for individual XML languages and move any compound language definitions to a separate layer (NVDL).