1. A method, comprising: computing a click relevance ranking of a first pair and a second pair based upon user log data, the first pair comprising a query and a first URL, the second pair comprising the query and a second URL, the computing comprising: reducing click bias associated with at least one of the first pair or the second pair by determining a normalized click rate; creating a directed acyclic graph of a relevance relationship between the first pair and the second pair; mapping the directed acyclic graph into a linear ordering; and using at least one of the reducing, the creating or the mapping to determine the click relevance ranking.