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Enhanced ER-diagram
Prof. Sin-Min Lee Depart ment of Computer Science

 Example: A library database contains a listing of indites that possess written books on various(a) subjects (one author per book). It also contains nurture about libraries that behave books on various subjects.

RELATIONSHIPS (Cont…)
Example: A library database contains a listing of authors that have written books on various subjects (one author per book). It also contains information about libraries that carry books on various subjects.
Entity frozens: authors, subjects, books, libraries

RELATIONSHIPS (Cont…)
Example: A library database contains a listing of authors that have written books on various subjects (one author per book). It also contains information about libraries that carry books on various subjects.




Entity objurgates: authors, subjects, books, libraries Relationship sets: wrote, carry, indexed

RELATIONSHIPS (Cont…)
undefendable matter index subject

title SS# authors call in carry salute libraries wrote books

isbn

RELATIONSHIPS (Cont…)
Subject matter index subject

title SS# authors name total address carry libraries wrote books

isbn

BINARY RELATIONSHIP B dexterity be: A binary relationship between entity set A and
1:1 Women marrying Men (function)
A women men N:1 Children marry mothers (function) having B

1:N Mothers having 1children (inverseAfunction) having mothers children M:N Students enrolled in a class 1 n
mothers having children A

n

B

B

students

enrolled

classes

A

B

 Entities and relationships ar distinguishable using various keys A key is a conclave of one or more attributes, e.g., social-security number, combination of name and social-security number. A superkey is a key defined either for an entity set or relationship set that uniquely identifies an entity, e.g., social-security number, phone number, combination of name and social-security number. A candidate key is a minimum superkey that...If you want to get a full essay, order it on our website: Ordercustompaper.com



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