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Deciding definability in FO2(<h,<v) on trees

Thomas Place ; Luc Segoufin.

We provide a decidable characterization of regular forest languages definable in FO2(<h,<v). By FO2(<h,<v) we refer to the two variable fragment of first order logic built from the descendant relation and the following sibling relation. In terms of expressive power it corresponds to a fragment of&nbsp;[&hellip;]

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Datalog Rewritings of Regular Path Queries using Views

Nadime Francis ; Luc Segoufin ; Cristina Sirangelo.

We consider query answering using views on graph databases, i.e. databases structured as edge-labeled graphs. We mainly consider views and queries specified by Regular Path Queries (RPQ). These are queries selecting pairs of nodes in a graph database that are connected via a path whose sequence of&nbsp;[&hellip;]

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Unary negation

Luc Segoufin ; Balder ten Cate.

We study fragments of first-order logic and of least fixed point logic that allow only unary negation: negation of formulas with at most one free variable. These logics generalize many interesting known formalisms, including modal logic and the $\mu$-calculus, as well as conjunctive queries and&nbsp;[&hellip;]

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