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IT420: Database Management and Organization

ER Model: part 2 13 January 2006

Adina Crăiniceanuwww.cs.usna.edu/~adina

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ER Model

Entities, attributes, identifiersHAS-A Relationships

Degree: binary, ternaryMaximum cardinalityMinimum cardinality

Weak entities ID-dependent entities; identifying relationships

IS-A RelationshipsInclusive, Exclusive

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Goals of This Lecture

Create ER model from user requirements

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ERwin Symbol Summary

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ERwin Symbol Summary (Continued)

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Forms, Reports and ER Model

User input: FormsReportsDiscussions

DB modeler: Entity-Relationship modelSame entities, relationships under the surface

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1:1 Strong Entity Relationships

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1:1 Strong Entity Relationships

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1:N Strong Entity Relationships

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1:N Strong Entity Relationships

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N:M Strong Entity Relationships

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N:M Strong Entity Relationships

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N:M Strong Entity Relationships

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The Association Pattern

Price column

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Association Class

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Entity vs. Attribute

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Multi-valued Attribute Entity

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Recursive Relationships

Recursive relationship: an entity has a relationship to itself

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1:N Recursive Relationship

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1:1 Recursive Relationship

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N:M Recursive Relationship

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Class Exercise

Draw ER diagram for a database used to manage IT420 class (at least 3 entities)

Specify entities, attributes, identifiersSpecify relationshipsSpecify cardinalities for relationships

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Highline University

The Highline University [HU] database will track such entities as:

CollegesDepartmentsFacultyStudents

We have gathered a set of HU reports that will be the source documents for a data model

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The College Report

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Data Model from the College Report

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The Department Report

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The DEPARTMENT / PROFESSOR Relatioship:Alternate Model 1: Using a 1:N Relationship

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The DEPARTMENT / PROFESSOR Relatioship:Alternate Model 1: Using a 1:N Relationship

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The DEPARTMENT / PROFESSOR Relatioship:Alternate Model 2: Using an N:M Relationship

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The DEPARTMENT / PROFESSOR Relatioship:Alternate Model 3: Using an Association Pattern

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The DEPARTMENT / PROFESSOR Relatioship:Alternate Model 4: Using a Association Patternand a 1:N Relationship

Chaired By /Chairs

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The Department Major Report

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Data Model with STUDENT Entity

Chaired By /Chairs

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The Student Acceptance Letter

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Data Model with Advises Relationship

Chaired By /Chairs

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Final Data Model

Chaired By /Chairs

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ER Modeling: Case StudyDrugwarehouse.com has offered you a free life-time supply of prescription drugs (no questions asked) if you design its database schema. Given the rising cost of health care, you agree. Here is the information that you gathered:Patients are identified by their SSN, and we also store their names and ageDoctors are identified by their SSN, and we also store their names and specialtyEach patient has one primary care physicianEach doctor has at least one patientDoctors prescribe drugs for patients