Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Region Algebra

  • Matthew Young-Lai
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_304

Definition

A region algebra is a collection of operators, each of which returns a set of regions as a result and takes as arguments one or more sets of regions. A region of a string is a pair of natural number positions (s, e) that correspond to the substring starting at s and ending at e. A position is a count of bytes, characters, or words from the beginning of the string.

Choosing a set of operators defines a particular region algebra. Operators are chosen for efficiency as well as utility. For example, if regions correspond to structure elements such as chapters and sections in a document, then many operators for querying structure conditions are useful and can be implemented efficiently. One example of such an operator is containedIn(X,Y) which takes two sets of regions X and Y and returns the subset of regions in X that are contained in some region of Y, i.e., {(sx, ex)∈X∣∃(sy, ey)∈Y(sxsy) ∧ (exey)}. A similar operator is contains(X,Y) which returns the subset of regions...

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Recommended Reading

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Sybase iAnywhereWaterlooCanada
  2. 2.Google, Inc.Mountain ViewUSA

Section editors and affiliations

  • Frank Tompa
    • 1
  1. 1.David R. Cheriton School of Computer ScienceUniv. of WaterlooWaterlooCanada