Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for document ranking. One of the methods includes receiving a request for one or more documents, obtaining a set of documents responsive to the request, and obtaining, from a user profile associated with a source of the request, representations of one or more topics of interest to a user. The method also includes selecting, from the set of documents, at least one document associated with a particular topic that matches at least one of the one or more topics of interest to the user, for the at least one selected document, obtaining a value corresponding to an inverse document frequency of documents associated with the particular topic in a corpus of documents, and generating a score for the at least one document based at least in part on the value corresponding to the inverse document frequency.

Abstract: Metadata is used to determine rules that can be applied to facts. In one embodiment, correlations are identified among types of objects and the attributes of the facts associated with those objects. In another embodiment, correlations are identified among types of objects, the attributes of the facts associated with the objects, and the format and/or range of the values of the facts having those attributes. When a correlation exists between objects of a given type and the attributes of the facts associated with objects of that type, a rule is created for objects of that type. The rule is applied to objects of the given type.