Session3-a

Session3-a - Session 3 ER to Relational Mapping CSCI-585...

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Session 3: ER to Relational Mapping CSCI-585 , Cyrus Shahabi Strong entity set with attributes a 1 , a 2 , …, a n : represent it as a table with n unique columns (one column per attribute). Example: …. Each row in this table corresponds to one entity of the entity set. We may add/delete/modify rows in the table. Weak entity set with attributes a 1 , a 2 , …, a n and an owner entity set with primary key b 1 , b 2 , …, b m : represent it as a table with n+m columns, one for each of { a 1 , a 2 , …, a n } U { b 1 , b 2 , …, b m }. b 1 , b 2 , …, b m is the foreign key of the resulting relation referring to the corresponding relation of the owner entity set. Example:
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(Idea: keep rows unique.) N-ary relationship set R with attributes a 1 , a 2 , …, a n among entity sets E i ‘s (say m entity sets): represent it as a table with n+m columns, one for each of { a 1 , a 2 , …, a n } U {prim-key(E 1 ), prim-key(E 2 ), …, prim-key(E m )}. Binary relationship set R with attributes a
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This document was uploaded on 05/16/2010.

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Session3-a - Session 3 ER to Relational Mapping CSCI-585...

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