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http://hdl.handle.net/1942/21032
Title: | Relative expressive power of downward fragments of navigational query languages on trees and chains | Authors: | HELLINGS, Jelle GYSSENS, Marc Wu, Yuqing Van Gucht, Dirk VAN DEN BUSSCHE, Jan VANSUMMEREN, Stijn Fletcher, George H. L. |
Issue Date: | 2015 | Publisher: | ACM | Source: | Cheney, James; Neumann, Thomas (Ed.). Proceedings of the 15th Symposium on Database Programming Languages, p. 59-68 | Abstract: | Motivated by the continuing interest in the tree data model, we study the expressive power of downward fragments of navigational query languages on trees. The basic navigational query language we consider expresses queries by building binary relations from the edge relations and the identity relation, using composition and union. We study the effects on the expressive power when we add transitive closure, projections, coprojections, intersection, and difference. We study expressiveness at the level of boolean queries and path queries, on labeled and unlabeled trees, and on labeled and unlabeled chains. In all these cases, we are able to present the complete Hasse diagram of relative expressiveness. In particular, we were able to decide, for each fragment of the navigational query languages that we study, whether it is closed under difference and intersection when applied on trees. | Keywords: | tree queries; expressive power; automata | Document URI: | http://hdl.handle.net/1942/21032 | Link to publication/dataset: | http://jhellings.nl/files/dbpl2015_paper.pdf | ISBN: | 978-1-4503-3902-5 | DOI: | 10.1145/2815072.2815081 | Rights: | Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Permissions@acm.org. Copyright is held by the owner/author(s). Publication rights licensed to ACM. | Category: | C1 | Type: | Proceedings Paper |
Appears in Collections: | Research publications |
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