July 2008
Intermediate to advanced
230 pages
4h 33m
English
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Chapter 6. E
E/R Entity/relationship.
E/R diagram See entity/relationship diagram.
E/R model See entity/relationship model.
E/R modeling See entity/relationship modeling.
E-relation See RM/T.
element See bag; set.
embedded dependency A dependency satisfied by some projection of some relvar.
Example: Consider relvar CTXD, with attributes C (course), T (teacher), X (text), and D (days) and predicate "Teacher T spends D days with textbook X on course C." Let the sole key for that relvar be {C,T,X}. Assume also that for a given course, the set of teachers and the set of texts are quite independent of each other. Then CTXD is in 6NFit can't be nonloss decomposed at all, other than trivially. Yet its projection on {C,T,X} satisfies the embedded multivalued ...
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