1. A method comprising: receiving a request to create unspecified relational database structures for storing, in a relational database, structured documents described by at least a first schema description that references a second schema description; in response to receiving the request: determining that the first schema description uses a first set of entities of the second schema description, wherein the second schema description includes the first set of entities and a second set of entities that are not used by the first schema description; and creating relational database structures corresponding to the first set of entities of the second schema description without creating relational database structures corresponding to the second set of entities of the second schema description; wherein the method is performed by one or more special-purpose computing devices.