NDLI: Logical definability and query languages over unranked trees

Content Provider	IEEE Xplore Digital Library
Author	Libkin, L. Neven, F.
Copyright Year	2003
Description	Author affiliation: Toronto Univ., Ont., Canada (Libkin, L.)
Abstract	Unranked trees, that is, trees with no restriction on the number of children of nodes, have recently attracted much attention, primarily as an abstraction of XML (Extensible Markup Language) documents. In this paper, we study logical definability over unranked trees, as well as collections of unranked trees, that can be viewed as databases of XML documents. The traditional approach to definability is to view each tree as a structure of a fixed vocabulary, and study the expressive power of various logics on trees. A different approach, based on model theory, considers a structure whose universe is the set of all trees, and studies definable sets and relations; this approach extends smoothly to the setting of definability over collections of trees. We study the latter, model-theoretic approach. We find sets of operations on unranked trees that define regular tree languages, and show that some natural restrictions correspond to logics studied in the context of XML pattern languages. We then look at relational calculi over collections of unranked trees, and obtain quantifier-restriction results that give us bounds on the expressive power and complexity. As unrestricted relational calculi can express problems complete for each level of the polynomial hierarchy, we look at their restrictions, corresponding and find several calculi with low (NC/sup 1/) data complexity that can express important XML properties like DTD validation and XPath evaluation.
Sponsorship	IEEE Comput. Soc. Tech. Committee on Math. Found. Comput. Assoc. Symbolic Logic Eur. Assoc. Theoretical Comput. Sci
Starting Page	178
Ending Page	187
File Size	393367
Page Count	10
File Format	PDF
ISBN	0769518842
ISSN	10436871
DOI	10.1109/LICS.2003.1210057
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2003-06-22
Publisher Place	Canada
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Database languages XML Automata Logic Relational databases Vocabulary Polynomials Spatial databases Web sites Navigation
Content Type	Text
Resource Type	Article
Subject	Mathematics Software

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