csce520-lect-er

csce520-lect-er - ENTITY-RELATIONSHIP (E/R) MODEL Database...

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Unformatted text preview: ENTITY-RELATIONSHIP (E/R) MODEL Database Systems- The Complete Book: Chapter 2 Self testing exercises: ◦ 2.1.3 and 2.1.4 ◦ 2.2.4 ◦ 2.3.1.b ◦ Any of the remaining exercises in the textbook Following lecture slides are modified from Jeff Ullman’s slides for Fall 2002 -- Stanford 12/13/11 CSCE 520 2 Reading and Exercises Informal Database Design Entity-relationship diagram Easy to convert to implementations (e.g., relational databases) 12/13/11 CSCE 520 3 Purpose Database: collection of entities and relationship among entities Entity: object that exists and distinguishable from other objects Entity set: collection of similar objects Attribute: property of an entity set ◦ Each entity in the set has the same properties 12/13/11 CSCE 520 4 Entity Sets Domain: set of permitted values for each attributes Attribute types: ◦ Simple vs. composite ◦ Single-valued v.s. multi-valued ◦ Derived 12/13/11 CSCE 520 5 Attributes Entity sets: diagrams Attributes: oval Relationship sets between entity sets: diamond 12/13/11 CSCE 520 6 E/R Diagram 12/13/11 CSCE 520 7 Example E/R Diagram Dog Name Breed Age License # Phone Weight Name Name Phone Address Owns Owner Kennel Pays Boards Current value of an entity set is the set of entities that belong to it Value of a relationship is a set of lists of currently related entities (one from each entity sets) 12/13/11 CSCE 520 8 Relationship Set Example Example of the Owns relation 12/13/11 CSCE 520 9 Owner Dog Mary Bruno Mary Panka Joe Warrior Viki Pepper John Buddy Number of entity sets participating in a relationship set Binary relationship set: two entity sets (most common) Multiway relationship set: connects more than two entity sets E.g., An owner frequents certain kennels for certain dogs ◦ Binary relationship can’t represent these requirements ◦ Need 3-way relationship 12/13/11 CSCE 520 10 Degree of Relationship Sets 12/13/11...
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This note was uploaded on 12/13/2011 for the course CSCE 520 taught by Professor Farkas during the Spring '11 term at South Carolina.

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csce520-lect-er - ENTITY-RELATIONSHIP (E/R) MODEL Database...

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