1. A system for identifying semantically relevant documents, comprising: an index comprising semantic index key terms from one or more documents; a query module to obtain a query and to identify semantic key terms of the query, wherein each of the query key terms is associated with information comprising use of the word and a grammatical role of the word; and a search module to look up the each of the query key terms and variants of the query key terms in the index based on the information; an identification module to identify one or more of the documents in the index as possible relevant candidates based on the look up; a candidate set generator to generate a potential match candidate set by filtering the possible relevant candidates; and a document matching module to identify at least one of the documents that match the query by comparing a semantic representation for each non-filtered potential match candidate in the set with a semantic representation for the query.