25. A document identification system for identifying a predetermined number of documents matching a query, comprising: a read-only memory containing a database containing identifications of documents in a document collection and defining a plurality of representations representing the contents of documents in the document collection, the collection comprising a plurality of documents; query means for defining the query containing a plurality of concepts; computer means responsive to the query containing a plurality of concepts, the computer means including matching means for matching the concepts to representations; sample selection means for iteratively selecting successive samples of a plurality of documents from the collection for examination, each sample containing fewer documents than the entire collection, and each successive sample containing documents different from each previous sample; processing means responsive to the sample selection means for calculating, during each iteration probabilities that documents contained in the sample contain representations that match the query and for identifying up to a preselected number of documents having the highest probabilities, the documents being identified during each iteration from a group consisting of the respective sample of documents and the documents identified during the next previous iteration, the preselected number being different for each iteration and no greater than the predetermined number; and output means outputting identifications of the predetermined number of documents identified by the processing means.
25. A document identification system for identifying a predetermined number of documents matching a query, comprising: a read-only memory containing a database containing identifications of documents in a document collection and defining a plurality of representations representing the contents of documents in the document collection, the collection comprising a plurality of documents; query means for defining the query containing a plurality of concepts; computer means responsive to the query containing a plurality of concepts, the computer means including matching means for matching the concepts to representations; sample selection means for iteratively selecting successive samples of a plurality of documents from the collection for examination, each sample containing fewer documents than the entire collection, and each successive sample containing documents different from each previous sample; processing means responsive to the sample selection means for calculating, during each iteration probabilities that documents contained in the sample contain representations that match the query and for identifying up to a preselected number of documents having the highest probabilities, the documents being identified during each iteration from a group consisting of the respective sample of documents and the documents identified during the next previous iteration, the preselected number being different for each iteration and no greater than the predetermined number; and output means outputting identifications of the predetermined number of documents identified by the processing means. 26. The system according to claim 25 further including threshold setting means responsive to the processing means for setting a probability threshold equal to the probability of a first identified document.