Concurrency and communication in Delta Prolog

We describe and exemplify the logic programming language Delta Prolog, an extension to Prolog to include AND-concurrency and interprocess communication. Besides its declarative semantics, its operational semantics, comprising distributed backtracking, is especially emphasized. The extension is obtained, at the language level, by introducing three additional goal types: splits, events, and choices. At the implementation level, the extension is provided by code in Prolog and C. A small number of core primitives facilitates portability. Currently Delta-Prolog supports distributed programs through the asynchronous execution of multiple instances of an extended C-Prolog.