UPDATES IN A TEMPORAL LOGIC PROGRAMMING LANGUAGE

Abstract

Starlog, a pure logic programming language including negation is introduced. It is shown that this language is capable of directly expressing the mutation and change of clauses within a database. This is the problem traditionally solved in Prolog with the semantically-unsatisfactory "assert" and "retract". The standard, minimal-model semantics for normal logic programs is preserved in Starlog, and no extensions are used beyond standard clausal logic. It is noted that by extending stratification to a "temporal stratification" the completion of such programs is guaranteed to be consistent. Some short, example programs are described and used to illustrate an effective and efficient bottom-up technique for executing the language based on connection graphs. The execution technique solves the problems of matching generated results against goals and of efficiently and correctly dealing with negations.