Entity Modeling

1
Entity Modeling

• Pratt Adamski, Ch 6

2
Design Methodology Data Modeling
The Pratt and Adamski approach is not a
standard MIS view.
3
Data Modeling

• CS
• Start with reports and forms
• Identify attributes
• Identify tables
• Normalize

• MIS Approach
• Start with a narrative description
• Identify entities
• Design table structure
• Check for normalization

4
MIS Data Modeling

• Top-down approach
• Begins with a model of the firm
• Focuses on tables and relationships
• Begins by modeling entities and adds attributes
  later
• Normalization used as a confirmation rather than
  design tool

5
Life Cycle

• Enterprise Design major components
• Entities and relationships in context
• Conceptual Design business needs
• Tables and attributes independent of DBMS
• Physical Design technology design
• Entities, attributes, constraints, associative
  tables, etc. as they will be built

6
Enterprise Design

• Determine the entities and relationships that
  interact with the proposed system.
• Dont model attributes, constraints or tables
  necessary to implement relational structures or
  sub-classes

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Enterprise Model
SalesRep
Customer
Order
Product
Supplier
8
Conceptual Design

• Determine the model of the system independent of
  the DBMS that will be used for physical
  implementation.
• System entities, primary keys, attributes,
  relationships, constraints. No associative
  entities, foreign keys or sub-classes.

9
Conceptual Model
SalesRep SalesRepID (PK) Name Address
Customer CustomerID (PK) Name Address
Product ProductNum (PK) Description Price Category
Order OrderNumber (PK) Date
10
Relational and Physical Design

• Produce a detailed model of the ultimate system.
• Model a complete normalized system. Then
  denormalize selectively to improve the
  operational characteristics of the final database.

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Relational Model
Customer CustomerID (PK) SalesRepID
(FK) Name Address
SalesRep SalesRepID (PK) Name Address
Product ProductNum (PK) Description Price Category
Order OrderNumber (PK) CustomerID (FK) Date
Order-Product ProdNum (PK/FK) OrderNum (PK/FK)
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Entity Modeling

• Represent each entity as a table
• Determine the attributes for each entity
• Determine the relationships among the entities

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Definition Schema Notation

• TableName( attributes )
• Primary keys are underlined or denoted PK
• Alternate keys are denoted AK
• Secondary keys are denoted SK
• Foreign keys are denoted FK
• Faculty(FacID, Name, Office, Dept (FK))

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E-R Diagrams (PA notation)

• Entities

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E-R Diagrams (PA notation)

• Relationships 1 to many

1
m
Department
Employee
Department
Employee
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E-R Diagrams (PA notation)

• Relationships many to many

m
n
Student
Class
Class
Student
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Data Modeling