F. Odeh, I. Tadjbakhsh
Archive for Rational Mechanics and Analysis
We study here the language Datalog (≠), which is the query language obtained from Datalog by allowing equalities and inequalities in the bodies of the rules. We view Datalog (≠) as a fragment of an infinitary logic Lw and show that Lw can be characterized in terms of certain two-person pebble games. This characterization provides us with tools for investigating the expressive power of Datalog (≠). As a case study, we classify the expressibility of fixed subgraph homeomorphism queries on directed graphs. S. Fortune, J. Hopcroft, and J. Wyllie (Theoret. Comput. Sci. 10 (1980), 111-121) classified the computational complexity of these queries by establishing two dichotomies, which are proper only if P ≠ NP. Without using any complexity-theoretic assumptions, we show here that the two dichotomies are indeed proper in terms of expressibility in Datalog (≠). © 1995 by Academic Press, Inc.
F. Odeh, I. Tadjbakhsh
Archive for Rational Mechanics and Analysis
Nimrod Megiddo
Journal of Symbolic Computation
Chai Wah Wu
Linear Algebra and Its Applications
Shu Tezuka
WSC 1991