1. A method for searching a database comprising: inputting a search string that comprises a plurality of search string arguments connected by one or more operators wherein each search string argument specifies a search criteria; computing a distance measure between a quantitative characterizations corresponding to each of one or more of the search criteria, and quantitative characterizations of each of a plurality of records; selecting records for inclusion in answer sets for each mth search criteria among the one or more search criteria based, at least in part, on a plurality of distance measures each involving a quantitative characterization corresponding to the mth search criteria, and a quantitative characterization corresponding to one of the plurality of records; for each kth operator of the search string performing an operation specified by the kth operator on answer sets that are arguments of the kth operator to form a kth answer set for the kth operator; for each nth record in the kth answer set for each kth operator, assigning a retrieval relevance value to the nth record in the kth answer set, wherein the retrieval relevance value is a mathematical function of one or more quantitative characterizations associated with the nth record in answer sets that are arguments of the kth operator.