Synonyms
Definition
Informally, two tuples are snapshot equivalent or weakly equivalent if all pairs of timeslices with the same time instant parameter of the tuples are identical.
Let temporal relation schema R have n time dimensions, D i , i = 1, ..., n, and let τi, i = 1, ..., n be corresponding timeslice operators, e.g., the valid timeslice and transaction timeslice operators. Then, formally, tuples x and y are weakly equivalent if
Similarly, two relations are snapshot equivalent or weakly equivalent if at every instant their snapshots are equal. Snapshot equivalence, or weak equivalence, is a binary relation that can be applied to tuples and to relations.
Key Points
The notion of weak equivalence captures the information content of a temporal relation in a...
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Recommended Reading
Aho A.V., Sagiv Y., and Ullman J.D. Efficient optimization of a class of relational expressions. ACM Trans. Database Syst., 4(4):435–454, 1979.
Aho A.V., Sagiv Y., and Ullman J.D. Equivalences among relational expressions. SIAM J. Comput., 8(2):218–246, 1979.
Gadia S.K. Weak temporal relations. In Proc. 4th ACM SIGACT-SIGMOD Symp. on Principles of Database Systems, 1985, pp. 70–77.
Jensen C.S. and Dyreson C.E. (eds.). A consensus glossary of temporal database concepts – February 1998 version. In Temporal Databases: Research and Practice, O. Etzion, S. Jajodia, S. Sripada (eds.). LNCS 1399, Springer-Verlag, Berlin, 1998, pp. 367–405.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2009 Springer Science+Business Media, LLC
About this entry
Cite this entry
Jensen, C.S., Snodgrass, R.T. (2009). Weak Equivalence. In: LIU, L., ÖZSU, M.T. (eds) Encyclopedia of Database Systems. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-39940-9_1533
Download citation
DOI: https://doi.org/10.1007/978-0-387-39940-9_1533
Publisher Name: Springer, Boston, MA
Print ISBN: 978-0-387-35544-3
Online ISBN: 978-0-387-39940-9
eBook Packages: Computer ScienceReference Module Computer Science and Engineering