Please use this identifier to cite or link to this item: http://hdl.handle.net/1942/10658
Title: Repetitions and permutations of columns in the semijoin algebra
Authors: LEINDERS, Dirk 
VAN DEN BUSSCHE, Jan 
Issue Date: 2009
Publisher: EDP Sciences
Source: RAIRO-THEORETICAL INFORMATICS AND APPLICATIONS, 43(2). p. 179-187
Abstract: Codd defined the relational algebra [E.F. Codd, Communications of the ACM 13 (1970) 377–387; E.F. Codd, Relational completeness of data base sublanguages, in Data Base Systems, R. Rustin, Ed., Prentice-Hall (1972) 65–98] as the algebra with operations projection, join, restriction, union and difference. His projection operator can drop, permute and repeat columns of a relation. This permuting and repeating of columns does not really add expressive power to the relational algebra. Indeed, using the join operation, one can rewrite any relational algebra expression into an equivalent expression where no projection operator permutes or repeats columns. The fragment of the relational algebra known as the semijoin algebra, however, lacks a full join operation. Nevertheless, we show that any semijoin algebra expression can still be simulated in a natural way by a set of expressions where no projection operator permutes or repeats columns.
Notes: Hasselt University and Transnational University of Limburg Agoralaan, gebouw D, 3590 Diepenbeek Belgium; dirk.leinders@uhasselt.be
Keywords: Database, relational algebra, semijoin algebra, projection
Document URI: http://hdl.handle.net/1942/10658
ISSN: 0988-3754
e-ISSN: 1290-385X
DOI: 10.1051/ita:2008023
ISI #: 000264879300001
Category: A1
Type: Journal Contribution
Validations: ecoom 2010
Appears in Collections:Research publications

Show full item record

Google ScholarTM

Check

Altmetric


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.