11. The method according to claim 10 , wherein the named entities are stored in the document index as document metadata.
10. A method comprising: extracting named entities from documents having corresponding document identifiers; creating and storing: a document index that indexes the named entities by the document identifiers to indicate whether the named entities occur in the documents; and an inverted index that indexes the document identifiers by word identifiers of words that occur in the documents, wherein the document index and the inverted index are at least partly created in advance of receiving a keyword query from a user; receiving the keyword query from the user, the keyword query comprising keywords; providing the keywords to the inverted index to identify individual document identifiers corresponding to individual matching documents that match one or more of the keywords of the keyword query; retrieving direct matching document entities that directly match at least one of the keywords of the keyword query; providing the individual document identifiers to the document index and retrieving co-occurring related named entities from the document index, wherein the co-occurring related named entities do not directly match the keywords of the keyword query but occur in the individual matching documents with the direct matching document entities; computing aggregate relevance scores for the co-occurring related named entities that occur in the individual matching documents; and returning one or more of the co-occurring related named entities in response to the keyword query based on the aggregate relevance scores, wherein at least the computing the aggregate relevance scores is performed using a processing unit.