1. A non-transitory computer-readable medium having stored thereon computer-executable instructions that if executed by a computer cause the computer to perform a method, the method comprising: locating a document identifier in an index entry, where an index entry stores a value to match to a term in a query; determining whether the index entry includes an expansion identifier; upon determining that the index entry includes an expansion identifier, producing an expanded document by expanding a document associated with the document identifier with a document associated with the expansion identifier; determining a relevance value corresponding to the relevance of the expanded document to the query; and providing a signal corresponding to the relevance value.
7. The non-transitory computer-readable medium of claim 1 , where the method includes providing a signal that identifies a set of documents whose relevance to the query exceeds a threshold.