Transcript Chapter 5

Chapter 5 – Part 1
Data Modelling with the
Entity-Relationship Model
Slide 1
Contents
A. Computer Company Problem
B. Solution
Slide 2
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. Solutions
1. Logical Analysis
2. Physical Analysis
Slide 5
1. Logical Analysis
1.1. Indentify Entity
1.2. Indentify Attributes
1.3. Identify Primary Identifier
1.4. Identify Alternative Identifier
1.5. Identify Mandatory Attributes
1.6. Identify Relationship
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1.1. Identify Entity
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1.2. Identify Attributes
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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 Attributes
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1.6. Identify Relationship
1.6.1. Identify Maximum Cardinalities
1.6.2. Identify Minimum Cardinalities
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1.6.1. Identify Maximum Cardinalities
1.6.1.1. Maximum Cardinalities Definition
1.6.1.2. Maximum Cardinalities on Diagram
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1.6.1.1. Maximum Cardinalities Definition
 Maximum Cardinalities 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 Cardinalities on Diagram
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1.6.2. Identify Minimum Cardinalities
1.6.2.1. Minimum Identifier Definition
1.6.2.2. Minimum Cardinalities on Diagram
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1.6.2.1. Minimum Identifier Definition
 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 Cardinalities on Diagram
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2. Physical Diagram
Slide 19
References
 Database Processing – Chapter 5
Data Modelling with the Entity-Relationship Model
David M. Kroenke
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