SYGRAF: implementing logic programs in a database style

It is shown how Horn logic programs can be implemented using database techniques, namely, mostly bottom-up in combination with certain top-down elements (as opposed to the top-down implementations of logic programs prevailing so far). The proposed method is sound and complete. It easily lends itself to a parallel implementation and is free of nonlogical features like backtracking. As an extension to the common approach to deductive databases, function symbols are allowed to appear in programs, and it is shown that much of database query optimization can be applied to optimize logic programs. An important advantage of present approach is its ability to evaluate successfully many programs that terminate under neither pure top-down nor bottom-up evaluation strategies