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)