Encyclopedia of Database Systems

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

Temporal Coalescing

  • Michael H. Böhlen
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_388

Definition

Temporal coalescing is a unary operator applicable to temporal databases that is similar to duplicate elimination in conventional databases. Temporal coalescing merges value-equivalent tuples, i.e., tuples with overlapping or adjacent timestamps and matching explicit attribute values. Tuples in a temporal relation that agree on the explicit attribute values and that have adjacent or overlapping timestamps are candidates for temporal coalescing. The result of operators may change if a relation is coalesced before applying the operator. For instance, an operator that counts the number of tuples in a relation or an operator that selects all tuples with a timestamp spanning at least 3 months are sensitive to temporal coalescing.

Historical Background

Early temporal relational models implicitly assumed that the relations were coalesced. Ben Zvi’s Time Relational Model [13, Chap. 8], Clifford and Croker’s Historical Relational Data Model (HRDM) [13, Chap. 1], Navathe’s Temporal...

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Copyright information

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

Authors and Affiliations

  1. 1.Free University of Bozen-BolzanoBozen-BolzanoItaly
  2. 2.University of ZurichZürichSwitzerland

Section editors and affiliations

  • Richard T. Snodgrass
    • 1
  • Christian S. Jensen
    • 2
  1. 1.University of ArizonaTucsonUSA
  2. 2.Aalborg UniversityAalborg ØstDenmark