DISCOUNT: A SYstem for Distributed Equational Deduction

The teamwork method ([De93], [AD93]) is a concept for distributing deduction systems on several processors. Its behavior is inspired by the behavior of a project team in a company. The general idea is, for a given problem, to explore the search space simultaneously in different directions and to allow for cross-fertilizations. This is accomplished by running a team of experts independently on several processors during a working phase. Each working phase is followed by a team meeting. Communication among the experts is restricted to these team meetings. During a team meeting each expert is evaluated by a referee. The task of a referee is twofold. Firstly, it evaluates the success of its associated expert regarding the given problem in general. Secondly, it extracts the best results produced by its expert. This information is passed to the supervisor. The supervisor then determines the best expert of the preceding working phase (the winner), incorporates the selected results of the losers into the winner's data base, creates a new team, transmits the updated data base of the winner to the members of the new team and this way starts a new working phase. For the first working phase the initial problem is transmitted. The combination of cooperation (good results are shared) and competition (only the winner can keep all its results) are the distinctive properties of the teamwork method. On the one hand, the "explosion" of the search space is avoided by suppressing most of the results of the inferior experts. On the other hand, in many cases it becomes possible to gain access to important points in the search space that cannot be reached by one expert alone in a reasonable amount of time. In section 2 of the paper we describe the DISCOUNT system ([DP92]), an implementation of the teamwork method for purely equational deduction. We demonstrate the power of the system by reporting experimental results in section 3.