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<p>A Datalog program <i>solves</i> a constraint satisfaction problem (CSP) if and only if it derives the goal predicate precisely on the unsatisfiable instances of the CSP. There are three Datalog fragments that are particularly important for finite-domain constraint satisfaction: <i>arc monadic Datalog</i>, <i>linear Datalog</i>, and <i>symmetric linear Datalog</i>, each having good computational properties. We consider the fragment of Datalog where we impose all of these restrictions simultaneously, i.e., we study <i>symmetric linear arc monadic (slam) Datalog</i>. We characterise the CSPs that can be solved by a slam Datalog program as those that have a gadget reduction to a particular Boolean constraint satisfaction problem. We also present exact characterisations in terms of a homomorphism duality (which we call <i>unfolded caterpillar duality</i>), and in universal-algebraic terms (using known minor conditions, namely the existence of <i>quasi Maltsev operations</i> and <i>k</i><i>-absorptive operations of arity</i> <i>nk</i>, for all <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(n,k \ge 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>,</mo> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>). Our characterisations also imply that the question whether a given finite-domain CSP can be expressed by a slam Datalog program is decidable.</p>

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Symmetric Linear Arc Monadic Datalog and Gadget Reductions

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  • 发表日期：

    2026年3月30日

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  • Manuel Bodirsky,
  • Florian Starke

摘要

A Datalog program solves a constraint satisfaction problem (CSP) if and only if it derives the goal predicate precisely on the unsatisfiable instances of the CSP. There are three Datalog fragments that are particularly important for finite-domain constraint satisfaction: arc monadic Datalog, linear Datalog, and symmetric linear Datalog, each having good computational properties. We consider the fragment of Datalog where we impose all of these restrictions simultaneously, i.e., we study symmetric linear arc monadic (slam) Datalog. We characterise the CSPs that can be solved by a slam Datalog program as those that have a gadget reduction to a particular Boolean constraint satisfaction problem. We also present exact characterisations in terms of a homomorphism duality (which we call unfolded caterpillar duality), and in universal-algebraic terms (using known minor conditions, namely the existence of quasi Maltsev operations and k-absorptive operations of arity nk, for all \(n,k \ge 1\) n , k ≥ 1 ). Our characterisations also imply that the question whether a given finite-domain CSP can be expressed by a slam Datalog program is decidable.