1. A method comprising: receiving a query in response to the query, constructing a composite search result that includes search result candidates from a plurality of candidate sources; wherein the step of constructing includes determining an amount of search results of each of said search result candidates based on at least a plurality of estimated attribute values of said composite search result; wherein each of said plurality of attribute values is a value that represents a measure of an attribute of the composite search result; and providing said composite search result as an answer to said query.