1. A method of automatically generating a description of a document, the method comprising: retrieving a document in response to a query, the query comprising a query phrase, the document including a plurality of sentences; calculating, by operation of a processor adapted to manipulate data within a computer system, for sentences of the document, a first count that includes a measure of a number of instances in which the query phrase occurs in the sentences; calculating, by operation of a processor adapted to manipulate data within a computer system, for sentences of the document, a second count that includes a measure of a number of instances in which any of one or more related phrases of the query phrase occurs in the sentences; calculating, by operation of a processor adapted to manipulate data within a computer system, for sentences of the document, a third count that includes a measure of a number of instances in which any of one or more phrase extensions of the query phrase occurs in the sentences, wherein a phrase extension is a super-sequence that begins with the query phrase; selecting one or more of the sentences of the document based on their respective first, second and third counts; and forming a description of the document from the selected sentences, wherein a phrase g j is a related phrase of another phrase g k where an information gain of g j with respect to g k exceeds a predetermined threshold, the information gain being a function of both actual and expected co-occurrence rates of g j and g k .