Validation of XML document against multiple schemas
E.g. Schematron + W3C XML Schema or Schematron + RELAX NG
One schema language is usually not enough for good validation
Validation of compound documents
NVDL can define how namespaces can be combined in document instances
NVDL can integrate existing schemas written in different schema language
Association between schema and document
Using !DOCTYPE
or xsi:schemaLocation
is not very good practice
NVDL can describe association between document type (namespace) and its schema(s)