Abstract: The relevance of a document to a given word or phrase is determined by calculating a function of whether the word or phrase occurs in the document and whether each member of a set of words or phrases related to the given word or phrase occurs in the document. A phrases may be included in this set if, out of all the documents in a collection that contain all the words of the phrase, the proportion of documents containing the phrase is greater than a predetermined value. Document relevance can be used to search for a document.