A Logic Coordination Language Based on the Chemical Metaphor

We describe Gammalog, a logic language whose semantics is based on the chemical metaphor typical of concurrent multiset rewriting. In fact, the language combines the ability of describing coordination by multiset transformation rules, as in GAMMA, with the execution model of logic programming in a strongly typed framework, as in Godel. We present the design choices, the language syntax, and its formal semantics. Gammalog has a standard model theoretic semantics expressed in terms of multiset rewritings; soundness and completeness results are proved with respect to extended SLD resolution. We present a prototype implementation of a compiler based on the original Godel implementation, which has been extended to support first class multisets. As an example of the expressive power of the language we provide a specification of a simple operating system.