Data%20Models

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Lecture 2

• Data Models

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Learning Objectives

• Why data models are important
• About the basic data-modeling building blocks
• What business rules are and how they affect
  database design
• How the major data models evolved, and their
  advantages and disadvantages
• How data models can be classified by level of
  abstraction

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• Data model
• Models abstraction of real-world Events
• DB Model
• Represents data structure and relationship
• Conceptual
• "What" is represented
• Implementation
• "How" represented

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CONCEPTUAL

• 3 types of associations
• ..one to many
• ..many to many
• ..one-to-one

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Implementation

• How data is represented in database ?

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Types of Data Models

• Hierarchical (see page 33)
• Network (see page 34)
• ..Simple
• ..Complex
• Relational (page 36)
• Object-Oriented (page 41)

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Hierarchical DB Model

• ex IMS by IBM
• basic unit is SEGMENT
• (similar to a record)
• root
• ..a child can have at the most one parent
• ..a parent can have many children
• navigation path
• .pre order traversing
• .post order traversing

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Advantages/Disadvantages

• Advtg
• allows data sharing
• data independence
• data integrity
• efficient for
• DISADVTG
• need to know some PHYSICAL level details
• data that do not conform to 1m
• complex and less flexible
• need to provide navigational path
• ad-hoc capabilities limited

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Network DB model

• SET
• OWNER and MEMBERS

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Advantages/Disadvantages

• Advantages
• .mn easy to implement
• .data integrity is maintained
• .data independence
• Disadvantages
• .Complex
• .no structural independence
• .navigation path

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Relational Model (p 36)

• Linking relational tables (page 37)
• Typically done through primary and foreign key
• Read the examples carefully

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Object-Oriented Model (page 41)

• Objects are defined (similar to entities)
• Objects contain data and procedures
• Objects can FIT with other objects
• Objects are reusable
• Objects have INHERITANCE property

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ER Data Model (page 38)

• Define
• Entities
• Attributes
• Relationships

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Degree of DATA abstraction

• Conceptual IT (hardware/software independent)
• Internal (DBMS dependent)
• External (end user orientation)
• Physical Model (actual implementation)

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• Supplemental reading
• www.itpapers.com