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Author Smith, Diane C. P. ♦ Smith, John Miles
Source ACM Digital Library
Content type Text
Publisher Association for Computing Machinery (ACM)
File Format PDF
Language English
Subject Keyword Aggregation ♦ Data definition language ♦ Data type ♦ Database design ♦ Knowledge representation ♦ Relational database ♦ Data abstraction ♦ Data structure
Abstract Aggregation is introduced as an abstraction which is important in conceptualizing the real world. Aggregation transforms a relationship between objects into a higher-level object. A new data type, called aggregate, is developed which, under certain criteria of “well-definedness,” specifies aggregation abstractions. Relational databases defined as collections of aggregates are structured as a hierarchy of n-ary relations. To maintain well-definedness, update operations on such databases must preserve two invariants. Well-defined relations are distinct from relations in third normal form. It is shown that these notions are complementary and both are important in database design. A top-down methodology for database design is described which separates decisions concerning aggregate structure from decisions concerning key identification. It is suggested that aggregate types, and other types which support real-world abstractions without introducing implementation detail, should be incorporated into programming languages.
Description Affiliation: Univ. of Utah, Salt Lake City (Smith, John Miles; Smith, Diane C. P.)
Age Range 18 to 22 years ♦ above 22 year
Educational Use Research
Education Level UG and PG
Learning Resource Type Article
Publisher Date 2005-08-01
Publisher Place New York
Journal Communications of the ACM (CACM)
Volume Number 20
Issue Number 6
Page Count 9
Starting Page 405
Ending Page 413


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Source: ACM Digital Library