A relational language for parallel programming

A parallel program often defines a relation not a function. The program constrains the output to lie in some relation R to the input, but the particular output produced during a computation can depend on the time behaviour of component processes. This suggests the use of a relational language as an applicative language for parallel programming. The Horn clause subset of predicate logic is a relational language with an established procedural interpretation for non-deterministic sequential computations [Kowalski 1974]. In this paper we modify and extend that interpretation to define a special purpose parallel evaluator.