Definition
The comprehension comes from ideas of mathematical set theory. It originated as a way of defining sets of values so as to avoid the famous paradoxes of early set theory, by starting from other well-defined sets and using some carefully chosen constructors and filters. The values in the sets could be tuples of basic values, which suits the relational model, or they could be object identifiers, which fits with ODMG object data models [2], or they could be tagged variant records which fit well with semi-structured data. They could even be sets, lists or bags defined by other comprehensions.
The abstract structure of a comprehension precisely describes almost all the computations done in functional query languages, despite their very different surface syntax. Better still, it allows many optimizations to be expressed as well defined mathematical transformations.
Key Points
Consider an example, using...
This is a preview of subscription content, log in via an institution.
Recommended Reading
Buneman P, Libkin L, Suciu D, Tannen V, Wong L. Comprehension syntax. ACM SIGMOD Rec. 1994;23(1):87–96.
Fegaras L, Maier D. Towards an effective calculus for Object Query Languages. In: Proceedings of ACM SIGMOD International Conference on Management of Data; 1995. p. 47–58.
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Section Editor information
Rights and permissions
Copyright information
© 2017 Springer Science+Business Media LLC
About this entry
Cite this entry
Gray, P.M.D. (2017). Comprehensions. In: Liu, L., Özsu, M. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4899-7993-3_5020-2
Download citation
DOI: https://doi.org/10.1007/978-1-4899-7993-3_5020-2
Received:
Accepted:
Published:
Publisher Name: Springer, New York, NY
Print ISBN: 978-1-4899-7993-3
Online ISBN: 978-1-4899-7993-3
eBook Packages: Springer Reference Computer SciencesReference Module Computer Science and Engineering