The language PLOP is a minimal language for studying polymorphism in a logical database programming language by means of parametrization of predicate names. The main idea is to introduce generic predicates which have two lists of parameters. While the second list contains the usual arguments, the first list contains parameters which are used as predicates in the rules defining the generic predicate. Through restriction in the use of predicate parameters it is possible to give a model theoretic semantics in a two step first order deduction. With the extensions we overcome the lack of predicate polymorphism in deductive database languages and increase their expressive power.

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