slide 1 chapter 05 – part 1 data modeling with the entity-relationship model
TRANSCRIPT
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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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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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1.6. 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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1.6.2. 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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References
Database Processing – Chapter 5Data Modelling with the Entity-Relationship Model
David M. Kroenke