August 2009
Intermediate to advanced
893 pages
26h 48m
English
Content preview from Database Systems: Concepts, Design and Applications
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6.4. Problems with E-R Models
Some problems, called connection traps, may arise when creating an E-R model. The connection traps normally occur due to a misinterpretation of the meaning of certain relationships. There are mainly two types of connection traps:
6.4.1. Fan Traps
In a fan trap, a model represents a relationship between entity types, but the pathway between certain entity occurrences is ambiguous. A fan trap may exist where two or more one-to-many (1:N) relationships fan out from the same entity. Fig. 6.19 (a) shows an example of fan trap problem.
Fig. 6.19. Example of fan trap and its removal
(a) An example of fan trap
(b) Semantic net of E-R model
(c) Restructured E-R model to eliminate fan trap
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