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Chapter 05 – Part 1

Data Modeling with the Entity-Relationship

Model

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Content

A. Computer Company ProblemB. Solution

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A. Computer Company Problem

ProgLtd is a company that places computer programmers at temporary jobs. They keep track on each programmer: the programmer's identification number, the programmer's last name, the programmer's first name, the programmer's rank (Junior, Senior ...), gender, his/her hourly rate and what languages the programmer knows.

Beside, each programmer has been issued a badge which is used for enter their office. On each badge has following information: badge’s code, the programmer's identification number, issued date.

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ProgLtd deals with clients who may require programmers who know a particular programming language. Once a programmer is assigned a temporary job, ProgLtd would like to keep track of when he/she started the job, the total number of hours he/she is expected to spend at job and the date he/she finished the job. That is in addition to the client name and phone number where the temp has been assigned.

Let’s design DB diagram for above requirements

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B. Solution

1. Logical Analysis2. Physical Analysis

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1. Logical Analysis

1.1. Identify Entity1.2. Identify Attribute1.3. Identify Primary Identifier1.4. Identify Alternative Identifier1.5. Identify Mandatory Attribute1.6. Identify Relationship

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1.1. Identify Entity

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1.2. Identify Attribute

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1.3. Identify Primary Identifier

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1.4. Identify Alternative Identifier

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1.5. Identify Mandatory Attribute

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1.6. Identify Relationship

1.6.1. Identify Maximum Cardinality1.6.2. Identify Minimum Cardinality

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1.6.1. Identify Maximum Cardinality

1.6.1.1. Maximum Cardinality Definition1.6.1.2. Maximum Cardinality on Diagram

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1.6.1.1. Maximum Cardinality Definition

Maximum Cardinality is the maximum number of entity instances that can participate in a relationship.

There are three types of maximum cardinality:•One-to-One [1:1]•One-to-Many [1:N]•Many-to-Many [N:M]

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1.6.1.2. Maximum Cardinality on Diagram

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1.6.2. Identify Minimum Cardinality

1.6.2.1. Minimum Identifier Definition1.6.2.2. Minimum Cardinality on Diagram

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1.6.2.1. Minimum Identifier Definition

Minimum Cardinality is the minimum number of entity instances that must participate in a relationship.

Minimums are generally stated as either zero or one:• IF zero [0] THEN participation in the

relationship by the entity is optional, and no entity instance must participate in the relationship.

• IF one [1] THEN participation in the relationship by the entity is mandatory, and at least one entity instance must participate in the relationship.

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1.6.2.2. Minimum Cardinality on Diagram

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2. Physical Diagram

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References

Database Processing – Chapter 5Data Modelling with the Entity-Relationship Model

David M. Kroenke

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