ch6 - Database System Concepts, 5th Ed . ©Silberschatz,...

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Unformatted text preview: Database System Concepts, 5th Ed . ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 6: Entity-Relationship Model Chapter 6: Entity-Relationship Model ©Silberschatz, Korth and Sudarshan 6.2 Database System Concepts - 5 th Edition, Oct 5, 2006 Chapter 6: Entity-Relationship Model Chapter 6: Entity-Relationship Model ■ Design Process ■ Modeling ■ Constraints ■ E-R Diagram ■ Design Issues ■ Weak Entity Sets ■ Extended E-R Features ■ Design of the Bank Database ■ Reduction to Relation Schemas ■ Database Design ■ UML ©Silberschatz, Korth and Sudarshan 6.3 Database System Concepts - 5 th Edition, Oct 5, 2006 Modeling Modeling ■ A database can be modeled as: ● a collection of entities, ● relationship among entities. ■ An entity is an object that exists and is distinguishable from other objects. ● Example: specific person, company, event, plant ■ Entities have attributes ● Example: people have names and addresses ■ An entity set is a set of entities of the same type that share the same properties. ● Example: set of all persons, companies, trees, holidays ©Silberschatz, Korth and Sudarshan 6.4 Database System Concepts - 5 th Edition, Oct 5, 2006 Entity Sets Entity Sets customer customer and and loan loan customer_id customer_ customer_ customer_ loan_ amount name street city number ©Silberschatz, Korth and Sudarshan 6.5 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Sets Relationship Sets ■ A relationship is an association among several entities Example: Hayes depositor A-102 customer entity relationship set account entity ■ A relationship set is a mathematical relation among n ≥ 2 entities, each taken from entity sets {( e 1 , e 2 , … e n ) | e 1 ∈ E 1 , e 2 ∈ E 2 , …, e n ∈ E n } where ( e 1 , e 2 , …, e n ) is a relationship ● Example: (Hayes, A-102) ∈ depositor ©Silberschatz, Korth and Sudarshan 6.6 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Set Relationship Set borrower borrower ©Silberschatz, Korth and Sudarshan 6.7 Database System Concepts - 5 th Edition, Oct 5, 2006 Relationship Sets (Cont.) Relationship Sets (Cont.) ■ An attribute can also be property of a relationship set. ■ For instance, the depositor relationship set between entity sets customer and account may have the attribute access-date ©Silberschatz, Korth and Sudarshan 6.8 Database System Concepts - 5 th Edition, Oct 5, 2006 Degree of a Relationship Set Degree of a Relationship Set ■ Refers to number of entity sets that participate in a relationship set. ■ Relationship sets that involve two entity sets are binary (or degree two). Generally, most relationship sets in a database system are binary....
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This note was uploaded on 02/17/2010 for the course CAS 6M03 taught by Professor Franek during the Spring '10 term at McMaster University.

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ch6 - Database System Concepts, 5th Ed . ©Silberschatz,...

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