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Towards Effective Parallel Logic Programming

Profile image of Fernando SilvaFernando Silva

Abstract

Abstract One of the advantages of logic programming (LP) and constraint logic programming (CLP) is the fact that one can exploit implicit parallelism in logic programs. Logic programs have two major forms of implicit parallelism: orparallelism (ORP) and and-parallelism (ANDP). In this work we survey some of work that has been taking place within the C LoPn project towards fast execution of logic programs.

Figures (5)
interesting alternative for the applications where copying does not work so well. As an example we are using the SBA to implement IAP. Parallel Tabling Ideally, one would want Prolog programs to be written as logical statements first, and for control to be tackled as a separate issue. In practice, the operational semantics of Prolog is given by SLD-resolution with depth-first search, a refutation strategy particu- larly simple and that matches current stack-based machines particularly well. Unfortu- nately, the limitations of SLD-resolution mean that Prolog programmers must be very aware of the Prolog computation rule throughout program development. For instance, logically correct programs will may have infinite loops.
interesting alternative for the applications where copying does not work so well. As an example we are using the SBA to implement IAP. Parallel Tabling Ideally, one would want Prolog programs to be written as logical statements first, and for control to be tackled as a separate issue. In practice, the operational semantics of Prolog is given by SLD-resolution with depth-first search, a refutation strategy particu- larly simple and that matches current stack-based machines particularly well. Unfortu- nately, the limitations of SLD-resolution mean that Prolog programmers must be very aware of the Prolog computation rule throughout program development. For instance, logically correct programs will may have infinite loops.
We use the example in Figure 1 in order to illustrate how parallelism can be exploited in the OPT model. The example assumes two workers, YW, and W,, and it represents a possible evaluation for a tabled program with ?- a(X). as the query goal.
We use the example in Figure 1 in order to illustrate how parallelism can be exploited in the OPT model. The example assumes two workers, YW, and W,, and it represents a possible evaluation for a tabled program with ?- a(X). as the query goal.
each processor labels its own subset of variables, communicating only when pruning a variable which connects different blocks allocated to different processors.
each processor labels its own subset of variables, communicating only when pruning a variable which connects different blocks allocated to different processors.
Table 4: PBCSP_1 and PBCSP_2: Execution Times for 1, 2, 4 and 8 Processors
Table 4: PBCSP_1 and PBCSP_2: Execution Times for 1, 2, 4 and 8 Processors

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