12. The method of claim 9 , wherein the plurality of pairs of entities comprises a first pair of entities, a first entity of the first pair being a document connected to a second entity of the first pair being a query, and wherein the strength value of the directed relationship from the document to the query is based on a quality of result statistic for the document as a search result for the query and quality of results statistics for the document as a search result for queries in search history data.
12. The method of claim 9 , wherein the plurality of pairs of entities comprises a first pair of entities, a first entity of the first pair being a document connected to a second entity of the first pair being a query, and wherein the strength value of the directed relationship from the document to the query is based on a quality of result statistic for the document as a search result for the query and quality of results statistics for the document as a search result for queries in search history data. 13. The method of claim 12 , wherein the strength value is calculated by dividing the quality of result statistic for the document as a search result for the query by a sum of quality results statistics for the document and all of the queries in the search history data for which the document is a search result.