Blackboards are a powerful form of communication based on the availability of a global data structure that can be accessed by any process in a controlled way. The use of blackboards results in a parallel language that exploits coarse-grained parallelism. This paper describes how to embed blackboard communication primitives in Prolog. The approach exploits implicit parallelism while preserving the sequential semantics of Prolog. The authors describe the blackboard behavior in Multi-BinProlog, an extension to BinProlog.

The authors make three primary extensions to BinProlog: a blackboard, that is, a central repository of terms, together with maintenance routines that permit multiple blackboards to be created; a set of blackboard manipulation routines--one write operation (tellt), two destructive get operations (gett and gett_nb), and two nondestructive get operations (readt and readt_nb); and a predicate to spawn a process.

Each extension is described in detail. Examples are given of their use in such problems as the dining philosophers problem, simulating an elevator system, creating bounded buffers, and lazy evaluation. The authors detail an algorithm to tell, get, or read a term from a blackboard. They give the performance of implementation using six benchmark problems. Local blackboard communication in BinProlog is five times faster than a comparable assert and retract in Sictus Prolog. Their authors’ implementation is on top of a thread library, and it permits blackboard communication that is safe and a high-level interface for multithreaded parallel machines.

The paper is well written, describes related work, and contrasts its approach with other efforts. The authors provide a useful extension to Prolog.