Any kind of programming language that SpecifieS output in termS of Some property and Some argumentS. For example, if Tom haS two brotherS, Dick and Harry, a relational language will reSpond to the query "Who iS Tom' S brother?" with either Dick or Harry. Notice that unlike {functional languageS}, relational languageS do not require a unique output for each predicate/argument pair. Prolog iS the beSt known relational language. (2004-05-17)