chapter4 - Outline Characteristics of entity relationship...

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Chapter 4 Entity Relationship (ER) Modeling BUS 173 Winter 2011 Dr. Hamouda Outline Characteristics of entity relationship components Define and Understand relationships Business rule representation Entity Relationship Diagram ER model forms the basis of an ER diagram Entity Relationship Diagram (ERD): represents conceptual database as viewed by end user is a graphical representation that depicts things of interest (entity with attributes) and relationships among them STUDENT LOAN receives < Entities are represented by a rectangle in an ERD Entities Entity types : collection of things of interest in an application Corresponds to table and not to row in relational environment Entity name, a noun, written in capital letters 5 Attributes Characteristics of entities Crow’s Foot notation: attributes written in attribute box below entity rectangle 6 Attributes (cont’d.) Required attribute : must have a value Optional attribute : may be left empty Identifiers : one or more attributes that uniquely identify each entity instance Composite identifier : primary key composed of more than one attribute
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7 Attributes (cont’d.) Composite attribute can be subdivided Exp. Address (street, city, zipcode, state) Simple attribute cannot be subdivided Exp. Age, name Single-value attribute can have only a single value Exp. Phone number 951-827-4551 Multivalued attributes can have many values Exp 1 . a person may have several phone numbers Exp 2 . a car may have may colors 8 Attributes (cont’d.) Multivalued attributes should be implemented follows: 1. Create several new attributes for each of the original multivalued attributes’ components Exp. Split CAR_COLOR into CAR_TOPCOLOR, CAR_BODYCOLOR, CAR_TRIMCOLOR 2. Create new entity composed of original multivalued attributes’ components Exp. New entity called COLOR and its attributes are TOPCOLOR, BODYCOLOR, TRIMCOLOR which will have a 1:M relationship with entity CAR Derived attribute : value may be calculated
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chapter4 - Outline Characteristics of entity relationship...

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