Transcription of Entity Relationship Model - WBUTHELP.COM
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Entity Relationship Model - WBUTHELP.COM
CHAPTER 2 Entity Relationship ModelThis chapter introduces the Entity - Relationship Model in detail. The chapter coversnumerous features of the Model , several of which can be omitted depending on theplanned coverage of the course. Weak Entity sets (Section ), design constraints(Section ) and aggregation (Section ), and the corresponding subsections ofSection (Reduction of an E-R Schema to Tables) can be omitted if time is short. Werecommend covering specialization (Section ) at least in some detail, since it isan important concept for object-oriented databases (Chapter 8).TheE-Rmodel itself andE-Rdiagrams are used often in the text. It is importantthat students become comfortable with them. TheE-Rmodel is an excellent contextfor the introduction of students to the complexity of database design. For a givenenterprise there are often a wide variety ofE-Rdesigns. Although some choices arearbitrary, it is often the case that one design is inherently superior to another.
specialization doctors test_name date time result ss# name name patients Dr−Patient insurance date−admitted date−checked−out dss# test−log test_id test performed_by
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