2006 | OriginalPaper | Chapter
Datalog and Constraint Satisfaction with Infinite Templates
Authors : Manuel Bodirsky, Víctor Dalmau
Published in: STACS 2006
Publisher: Springer Berlin Heidelberg
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We relate the expressive power of Datalog and constraint satisfaction with infinite templates. The relationship is twofold: On the one hand, we prove that every non-empty problem that is closed under disjoint unions and has Datalog width one can be formulated as a constraint satisfaction problem (CSP) with a countable template that is
ω-categorical
. Structures with this property are of central interest in classical model theory. On the other hand, we identify classes of CSPs that can be solved in polynomial time with a Datalog program. For that, we generalise the notion of the
canonical Datalog program
of a CSP, which was previously defined only for CSPs with finite templates by Feder and Vardi. We show that if the template Γ is
ω
-categorical, then CSP(Γ) can be solved by an (
l
,
k
)-Datalog program if and only if the problem is solved by the canonical (
l
,
k
)-Datalog program for Γ. Finally, we prove algebraic characterisations for those
ω
-categorical templates whose CSP has Datalog width (1,
k
), and for those whose CSP has strict Datalog width
l
.
Topic:
Logic in Computer Science, Computational Complexity.