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Data Analysis for Database Design, 3rd Edition
book

Data Analysis for Database Design, 3rd Edition

by David Howe
May 2001
Intermediate to advanced content levelIntermediate to advanced
336 pages
14h 36m
English
Butterworth-Heinemann
Content preview from Data Analysis for Database Design, 3rd Edition
involves only those employees who are salespersons; the Designs relationship involves
only those employees who are designers. It is usual to insist that the subtypes of a given
supertype are disjoint, in which case Fig. 13.3 could not model a situation in which an
employee could be both a salesperson and a designer.
Question
1. Which of the following restrictions do you think should apply to the use of the terms
entity subtype and entity supertype?
(a) an entity subtype must have the same identifier as its supertype;
(b) an entity subtype must have obligatory participation in its relationship with its
supertype;
(c) an entity subtype must have non-obligatory ...
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Publisher Resources

ISBN: 9780750650861