29. The system of claim 21 , wherein selecting, from the set S, a set V of quantity p representative documents, for a cluster Ci of the set C, that maximizes a diversity function comprises: initializing an arbitrary set of quantity p documents from the set S as the set V; and iteratively, until no further swap of a document from the set V results in an increase in a sum of pairwise distances of documents in the set V: determining whether swapping a document d from the set V with a document d′ that is paired with the document d increases a sum of pairwise distances of documents in the set V, and swapping the document d from the set V with a document d′ that is paired with the document d when determining that swapping increases the sum of pairwise distances of documents in the set V.
21. A system comprising: one or more computer processors; and one or more non-transitory computer readable devices that include instructions that, when executed by the one or more computer processors, causes the processors to perform operations, the operations comprising: identifying, with one or more processors, a set T of query terms; selecting, with the one or more processors, candidate documents D that each satisfy one or more of the terms of the set T; selecting, from the candidate documents D, a set S of quantity k of the candidate documents D based on a weighted-coverage function ƒ for the set T of terms; pairing each document in the set S with another document in the set S based on a distance between the paired documents; generating, with the one or more processors, a set C of clusters from the paired documents, each cluster in the set C being associated with one or more topics of the query terms; selecting, with the one or more processors, from the set S, a set V of quantity p documents, for one or more clusters of the set C, based on a diversity function, wherein the diversity function is expressed as (Σ 1≦i≦k, 1≦j≦p Σ 1≦i′≦k′, 1≦j′≦p GJD(D i j , D i′ j′ )); and providing for presentation the set V of documents as representative documents that cover one or more topics associated with the one or more clusters.