Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

However, given sufficient computing resources, it is possible to perform the
unification of A(X) with A(1), A(2) and A(3) in parallel (vide fig. 22.9 ). Such
concurrent unification of A(X) with OR- clauses A(1), A(2) and A(3) is called
OR-parallelism. The prime difficulty with OR- parallelism, with respect to the
last example, is the propagation of the correct bindings of variables to P(X).
This, however, calls for some knowledge about the existence of P(3) as a head
of some clauses. Perhaps, by maintaining concurrency of AND as well as ORparallelism
with the help of synchronization signals, this could be made
possible in future PROLOG machines.
Fig. 22.9: Demonstrating the concurrent resolution of a clause with
three OR clauses.
c) Stream Parallelism
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main ←b, c, d , P(1).
main ← A (X), P(X).
Stream parallelism occurs in PROLOG, when the literals pass a stream of
variable bindings to other literals, each of which is operated on concurrently.
Literals producing the variable bindings are called producers, while the
literals that use these bound values of variables are called consumers. As an
example, consider the following logic program :
1. main ← Int (N), Test (N), Print(N).
2. Int (0) ←
3. Int (N) ← Int ( M ), N is M + 1.
main ←e, f, g, P (2).
main← h, i, P (3).
In the above program, Int (N) produces the value of N, which is passed
on to Test (N) and Print (N) in succession. However, the procedure for Test
(N) and Print(N) may be executed with old bindings of N, while new
bindings of N may be generated concurrently for alternative solutions. Such
parallelism is referred to as Stream Parallelism. Stream parallelism has
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