Determinacy and determinacy analysis

One attractive, unique feature of logic programming languages is their ability to succinctly and declaratively express search. The alternatives of a search can be speci ed by a set of clauses de ning the same predicate. By backtracking, considering in turn each of these clauses, the di erent alternatives are explored until a solution (if it exists) is found. However, though backtracking is essential for predicates that deploy search, typically, many predicates of the programs are deterministic, and most queries to the program have no more than one solution. Providing for non-determinism can slow down the execution of a program on a uni-processor and limit the scope for parallel execution on a multi-processor. As a consequence, programmers are often forced to resort to the non-logical features of the language to ensure any determinacy is fully exploited. A number of papers on determinacy and its detection have been published. However, because of the diversity of applications for determinacy analysis, there has been a similar diversity of de nitions of determinacy and its related concepts. This paper reformulates the determinacy de nitions in a uniform framework; identifying and contrasting the di erent approaches. Techniques for detecting and exploiting determinacy are also reviewed together with some directions for future research.