8. A system comprising: one or more processors; and a computer-readable medium coupled to the one or more processors having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: defining query extraction criteria, the query extraction criteria configured to identify queries related to a subject relevance; identifying a candidate query from the queries stored in a query log according to the extraction criteria; generating relevancy scores for a first set of web documents, each relevancy score associated with a corresponding web document in the first set of web documents and being a measure of the relevance of the candidate query to the web document, the generating comprising defining proper subset criteria, the proper subset criteria configured to identify a proper subset of web documents from a collection of web documents as the first set of web documents, the proper subset of web documents related to the subject relevance; selecting web documents having an associated relevancy score that exceeds a relevancy threshold; generating a query-page candidate tuple from the selected web documents and the candidate query, the query-page candidate tuple including data specifying the candidate query and the selected web documents; generating a first intent measure related to the first set of web documents, the first intent measure being based on a vector of terms identified in the first set of web documents; searching a second set of web documents with the candidate query, the second set of web documents including the first set of web documents and additional web documents; generating a second intent measure from web documents identified by the search of the second set of web documents, the second intent measure being based on a vector of terms identified in the second set of web documents; filtering the web documents in the query-page candidate tuple based on the first intent measure and the second intent measure; storing the query-page candidate tuple as a query-page tuple; comparing the query-page tuple to an advertisement group, the advertisement group being an association of keywords and an advertisement; determining, based on the comparison, that the query-page tuple is relevant to the advertisement group, and in response to the determination associating the candidate query and at least one web document of the query-page tuple with the advertisement group; and providing the advertisement in response to a query that includes the candidate query based on the association of the candidate query with the advertisement group.
8. A system comprising: one or more processors; and a computer-readable medium coupled to the one or more processors having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations comprising: defining query extraction criteria, the query extraction criteria configured to identify queries related to a subject relevance; identifying a candidate query from the queries stored in a query log according to the extraction criteria; generating relevancy scores for a first set of web documents, each relevancy score associated with a corresponding web document in the first set of web documents and being a measure of the relevance of the candidate query to the web document, the generating comprising defining proper subset criteria, the proper subset criteria configured to identify a proper subset of web documents from a collection of web documents as the first set of web documents, the proper subset of web documents related to the subject relevance; selecting web documents having an associated relevancy score that exceeds a relevancy threshold; generating a query-page candidate tuple from the selected web documents and the candidate query, the query-page candidate tuple including data specifying the candidate query and the selected web documents; generating a first intent measure related to the first set of web documents, the first intent measure being based on a vector of terms identified in the first set of web documents; searching a second set of web documents with the candidate query, the second set of web documents including the first set of web documents and additional web documents; generating a second intent measure from web documents identified by the search of the second set of web documents, the second intent measure being based on a vector of terms identified in the second set of web documents; filtering the web documents in the query-page candidate tuple based on the first intent measure and the second intent measure; storing the query-page candidate tuple as a query-page tuple; comparing the query-page tuple to an advertisement group, the advertisement group being an association of keywords and an advertisement; determining, based on the comparison, that the query-page tuple is relevant to the advertisement group, and in response to the determination associating the candidate query and at least one web document of the query-page tuple with the advertisement group; and providing the advertisement in response to a query that includes the candidate query based on the association of the candidate query with the advertisement group. 14. The system of claim 8 , wherein: comparing the query-page candidate tuple to an advertisement group comprises comparing the data specifying the at least one web document to data specifying a landing page of the advertisement group's associated advertisement; and determining that the query-page candidate tuple is relevant to the advertisement group comprises determining that the at least one web document matches the landing page of the advertisement group's associated advertisement, and in response determining that the query-page candidate tuple is relevant to the advertisement group.