Patent ID: 7401073

Claim:
A method for searching a document collection that includes a plurality of documents that are respectively associated with one or more categories and contain terms, the method comprising: providing an index of the terms indicating the documents in which the terms appear; estimating a first statistical distribution of each of at least some of the terms in the index over the documents in the collection; estimating a second statistical distribution of each of at least some of the categories over the documents in the collection; accepting a query comprising one or more of the terms and a specified category restriction referring to at least one of the categories; computing a local term distribution, which is indicative of occurrence frequencies of at least one of the terms in the query within the specified category restriction, using the first and second estimated statistical distributions; determining a category-specific score for the at least one of the terms responsively to the local term distribution within the specified category restriction; and applying the query to the index using the category-specific score so as to return a response, wherein estimating the first statistical distribution comprises constructing term histograms of the at least some of the terms in the index, wherein estimating the second statistical distribution comprises constructing category histograms of the at least some of the categories, and wherein constructing the term and category histograms comprises mapping the documents in the collection to bins of the histograms, and wherein computing the local term distribution comprises determining a category restriction histogram based on the category histogram of the at least one of the categories responsively to the category restriction, and multiplying the category restriction histogram by the term histogram of the at least one of the terms in the query so as to produce a localized term histogram.