Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees

Jelle Hellings; Marc Gyssens; Yuqing Wu; Dirk van Gucht; Jan van den Bussche; Stijn Vansummeren; George H.L. Fletcher

doi:10.1016/j.is.2019.101467

Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees

Jelle Hellings, Marc Gyssens (Corresponding author), Yuqing Wu, Dirk van Gucht, Jan van den Bussche, Stijn Vansummeren, George H.L. Fletcher

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Research output: Contribution to journal › Article › Academic › peer-review

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Abstract

Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, projections, coprojections, intersection, and difference; this for Boolean queries and path queries on labeled and unlabeled structures. In all cases, we present the complete Hasse diagram. In particular, we establish, for each query language fragment that we study on trees, whether it is closed under difference and intersection.

Original language	English
Article number	101467
Number of pages	16
Journal	Information Systems
Volume	89
DOIs	https://doi.org/10.1016/j.is.2019.101467
Publication status	Published - Mar 2020

Keywords

Boolean queries
Downward query language fragments
Path queries
Relational calculus with transitive closure
Relative expressive power
Tree data model

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10.1016/j.is.2019.101467

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title = "Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees",

abstract = "Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries are built from the identity relation and edge relations using composition and union. We study the effects on relative expressiveness when we add transitive closure, projections, coprojections, intersection, and difference; this for Boolean queries and path queries on labeled and unlabeled structures. In all cases, we present the complete Hasse diagram. In particular, we establish, for each query language fragment that we study on trees, whether it is closed under difference and intersection.",

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Comparing the expressiveness of downward fragments of the relation algebra with transitive closure on trees. / Hellings, Jelle; Gyssens, Marc (Corresponding author); Wu, Yuqing; van Gucht, Dirk; van den Bussche, Jan; Vansummeren, Stijn; Fletcher, George H.L.

In: Information Systems, Vol. 89, 101467, 03.2020.

Research output: Contribution to journal › Article › Academic › peer-review

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AU - Vansummeren, Stijn

AU - Fletcher, George H.L.

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