A method is disclosed that can be used to reduce the size of the indexes 130 of structured-documents 150. The method uses the schema 110 of structured documents 180, in particular XML documents, to determine the existence of certain deterministic relationships 140 among the indexing components 170. Using such knowledge when indexing the data and formulating query execution plans can greatly reduce the size of the indices 170 and allow querying of such documents more efficiently.