14. A computer program product, encoded on a non-transitory computer-readable medium, operable to cause data processing apparatus to perform operations comprising: identifying a plurality of identities stored in a repository of identities, each identity corresponding to an expert of one or more topics; identifying a plurality of topics stored in a repository of information, each topic i) describing information included by a document of a corpus of documents and ii) distinguishing the document from the remaining documents of the corpus of documents, the plurality of topics including the one or more topics; and processing each document in the corpus of documents, the processing including: identifying one or more identities of the plurality of identities that occur within the document, identifying one or more topics of the plurality of topics that occur within the document, for each identity that occurs within the document, determining an identity score for the identity with respect to the document, the identity score indicating a degree of relevance between the associated identity and the document, for each topic that occurs within the document, determining a topic score for the topic with respect to the document, the topic score indicating a degree of relevance between the associated topic and the document, identifying one or more combinations of i) the one or more identities that occur within the document, and ii) the one or more topics that occur within the document, for each identified combination, determining an aggregate score for the document based on the identity score associated with the combination for the document and the topic score associated with the combination for the document; and aggregating, for each identified combination, the aggregate score of each document of the corpus of documents for the identified combination to define a composite score of the identified combination across the corpus of documents.
19. The program product of claim 14 , where determining the topic score for the topic with respect to the document includes determining the topic score based on features of occurrence of the topic in the document.