Database abstractions

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.

REFERENCES

Note: OCR errors may be found in this Reference List extracted from the full text article. ACM has opted to expose the complete List rather than only correct and linked references.

	1	E. F. Codd, A relational model of data for large shared data banks, Communications of the ACM, v.13 n.6, p.377-387, June 1970 [doi>10.1145/362384.362685]
	2	Codd, E.F. Further normalization of the data base relational model. In Courant Computer Science Symposia 6: Data Base Systems, Prentice-Hall, Englewood Cliffs, N.J., May 1971, pp. 33-64.
	3	Codd, E.F. Relational completeness of data base sublanguages. In Courant Computer Science Symposia 6: Data Base Systems, Prentice-Hall, Englewood Cliffs, N.J., May 1971, pp. 65-98.
	4	Codd, E.F. Recent investigations in relational data base systems. Information Processing 74, North-Holland Pub. Co., Amsterdam, 1974, pp. 1017-1021.
	5	James P. Fry , Edgar H. Sibley, Evolution of Data-Base Management Systems, ACM Computing Surveys (CSUR), v.8 n.1, p.7-42, March 1976 [doi>10.1145/356662.356664]
	6	Hoare, C.A.R. Notes on data structuring. In AP1C Studies in Data Processing No. 8: Structured Programming, Academic Press, New York, 1972, pp. 83-174.
	7	Barbara Liskov , Stephen Zilles, Programming with abstract data types, Proceedings of the ACM SIGPLAN symposium on Very high level languages, p.50-59, March 28-29, 1974, Santa Monica, California, United States
	8	Hans Albrecht Schmid , J. Richard Swenson, On the semantics of the relational data model, Proceedings of the 1975 ACM SIGMOD international conference on Management of data, May 14-16, 1975, San Jose, California [doi>10.1145/500080.500110]
	9	Senko, M.E., Altman E.B., Astrahan, M.M., and Fehder, P.L. Data structures and accessing in data-base systems. IBM Syst. J. 12, 1 (1973), 30-93.
	10	John Miles Smith , Diane C. P. Smith, Database abstractions: aggregation and generalization, ACM Transactions on Database Systems (TODS), v.2 n.2, p.105-133, June 1977 [doi>10.1145/320544.320546]
	11	Robert W. Taylor , Randall L. Frank, CODASYL Data-Base Management Systems, ACM Computing Surveys (CSUR), v.8 n.1, p.67-103, March 1976 [doi>10.1145/356662.356666]
	12	Wirth, N. The programming language PASCAL. Acta Inforrnatica 1, 1 (1971), 35-63.
	13	Woods, W.A. What's in a link: foundations for semantic networks. In Representation and Understanding, Academic Press, New York, 1975, pp. 35-82.