Treffer: PARLOG86 AND THE DINING LOGICIANS.

This article provides insights on the Parlog86, a logic programming language. The emphasis in systems programming is somewhat different from artificial intelligence or database applications. This design decision brings indeterminism to logic programming. In the theory of automata, a determinate automaton traverses one specific path for each possible input. An indeterminate automaton has points in the computation where it chooses one out of several alternative branches to follow. This choice is not dependent on the original input. When a non-determinate automation reaches a branch point, it traverses all possible branches either in turn or together. In this sense Prolog is non-deterministic: all the alternative clauses are tried. Parlog86 is indeterminate: only one clause is pursued. Allowing the candidate clauses to be those for which the call unifies with the head is too liberal a regime for indeterminism. For example, in the partition relation if one of the two parallel clauses is a candidate the other must necessarily be so. An arbitrary choice at this stage has up to a 50 percent chance of failing. An operating system that had a 50 percent chance of failing should be unthinkable.