A Linear Algebraic Approach to Datalog Evaluation

In this paper, we propose a fundamentally new approach to Datalog evaluation. Given a linear Datalog program DB written using N constants and binary predicates, we first translate if-and-only-if completions of clauses in DB into a set Eq(DB) of matrix equations with a non-linear operation where relations in MDB, the least Herbrand model of DB, are encoded as adjacency matrices. We then translate Eq(DB) into another, but purely linear matrix equations tildeEq(DB). It is proved that the least solution of tildeEq(DB) in the sense of matrix ordering is converted to the least solution of Eq(DB) and the latter gives MDB as a set of adjacency matrices. Hence computing the least solution of tildeEq(DB) is equivalent to computing MDB specified by DB. For a class of tail recursive programs and for some other types of programs, our approach achieves O(N³⁾ time complexity irrespective of the number of variables in a clause since only matrix operations costing O(N³⁾ or less are used. We conducted two experiments that compute the least Herbrand models of linear Datalog programs. The first experiment computes transitive closure of artificial data and real network data taken from the Koblenz Network Collection. The second one compared the proposed approach with the state-of-the-art symbolic systems including two Prolog systems and two ASP systems, in terms of computation time for a transitive closure program and the same generation program. In the experiment, it is observed that our linear algebraic approach runs 10¹ ~ 10⁴ times faster than the symbolic systems when data is not sparse. To appear in Theory and Practice of Logic Programming (TPLP).