Exploiting type analysis for unification in a distributed environment

Unification, in distributed implementations of logic programming, involves sending and receiving messages to access data structures spread among diffe rent nodes. In traditional implementations, processes access remote data st ructures by exchanging messages which carry either the overall data structu res or only remote references to them. Intermediate but fixed solutions are also possible. These fixed policies can be far from optimal on various cla sses of programs and may induce substantial overhead. This paper presents a n implementation scheme for distributed logic programming which consists of tailoring the copying level for each procedure argument. The scheme is bas ed on a consumption specification which describes the way each procedure "c onsumes" its arguments locally. Consumption specification avoids unnecessar y copying and allows to request data structures globally. The consumption s pecification (or its approximation) can be obtained through a static analys is inspired by traditional type analyses. The paper presents two implementa tions which exploit the consumption specification. The low-level implementa tion extends the Warren abstract Machine with instructions and data structu res for exploiting the consumption specification during code compilation. T he high-level implementation is based on attributed variables in order to c apture and implement, at a higher-level, distributed unification. Experimen tal results of the high-level implementation on a network of workstations s how the potential of the approach.