The Multipath Parallel Execution Model for Prolog

In this paper, a novel execution model for Prolog is presented. This execution model, called Multipath, follows a partial breadth-rst traversing of the SLD-tree combined with the traditional depth-rst search strategy. The paper also presents an Abstract Machine that implements the Multipath execution model. An interpreter for this Abstract Machine has been developed for both sequential and parallel machines. Performance results show that Multipath outperforms the conventional depth-rst execution model in a sequential environment, especially for combinatorial search problems. In addition, Multipath exhibits a new type of parallelism called path parallelism. This type of parallelism is ne-grained but it can be exploited very eeciently in terms of additional software/hardware cost since the amount of synchronization and data sharing that it requires is very low. Performance gures show that having a small number of units working in parallel can be very cost-eeective.