A method of validating a document structured in accordance with a first schema and with respect to a second schema saves processing time by using information about relationships between the first schema and second schema and the document's conformance to the first schema to determine the document's validity in the second schema. The element type definitions of the XML or other document cast in the first schema are examined to determine if any element conforming to element types in the first schema is always invalid in the second schema. If any content conforming to always invalid element types is present in the document, the document can be immediately invalidated with respect to the second schema without further processing. Any content conforming to element types in the first schema that are subsumed by element types in the second schema can be immediately validated with respect to the second schema.