csce520-lect2 - ENTITYRELATIONSHIP(E/R) MODEL...

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ENTITY-RELATIONSHIP (E/R)  MODEL
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12/13/11 CSCE 520 - Fall 2005 2 Reading and Exercises 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
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12/13/11 CSCE 520 - Fall 2005 3 Purpose Informal Database Design Entity-relationship diagram Easy to convert to implementations (e.g.,  relational databases)
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12/13/11 CSCE 520 - Fall 2005 4 Entity Sets 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
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12/13/11 CSCE 520 - Fall 2005 5 Attributes  Domain: set of permitted values for each  attributes Attribute types:  Simple vs. composite  Single-valued v.s. multi-valued Derived 
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12/13/11 CSCE 520 - Fall 2005 6 E/R Diagram Entity sets: diagrams Attributes: oval Relationship  sets between entity sets:  diamond
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12/13/11 CSCE 520 - Fall 2005 7 Example E/R Diagram Dog Name Breed Age License # Phone Weight Name Name Phone Address Owns Owner Kennel Pays Boards
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12/13/11 CSCE 520 - Fall 2005 8 Relationship Set 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)
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12/13/11 CSCE 520 - Fall 2005 9 Example Example of the Owns relation Owner Dog Mary Bruno Mary Panka Joe Warrior Viki Pepper John Buddy
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12/13/11 CSCE 520 - Fall 2005 10 Degree of Relationship Sets 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
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This note was uploaded on 12/13/2011 for the course CSCE 522 taught by Professor Farkas during the Fall '11 term at South Carolina.

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csce520-lect2 - ENTITYRELATIONSHIP(E/R) MODEL...

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