csce520-lect-er - ENTITYRELATIONSHIP(E/R MODEL...

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ENTITY-RELATIONSHIP (E/R)  MODEL
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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
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Informal Database Design Entity-relationship diagram Easy to convert to implementations (e.g.,  relational databases) 12/13/11 CSCE 520  3 Purpose
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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
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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 
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Entity sets: diagrams Attributes: oval Relationship  sets between entity sets: diamond 12/13/11 CSCE 520  6 E/R Diagram
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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
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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
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Example Example of the Owns relation 12/13/11 CSCE 520  9 Owner Dog Mary Bruno Mary Panka Joe Warrior Viki Pepper John Buddy
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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
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