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Goals of designing a database
- Eliminate redundancy
- Eliminate inconsistency
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Design phases
- Initial
- Conceptual
- Logical
- Normalization
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Initial design phase
- Gather and summarize functional and data requirements from the user
- Identify entities, attributes and relationships
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Conceptual design phase
- Choose a conceptual model (e.g ERM)
- Represent data requirements using chosen model
- Don't worry about implementation at this step
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Logical design phase
- Map conceptual model to implementation model
- Forming relations, objects etc
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Normalization phase
- Test for good design
- Correct design errors
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Entity-relationship model
- High level visual specification of a database schema
- Represents entities, attributes and relationships
- Supports specification contraints
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Entity
A visible or invisible object in the real world
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Entity set
- A set of entities of the same type
- A.k.a entity type
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Attributes
- Properties that describe all members of an entity set
- Each entity has it's own value for each attribute
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Relationship
Association among two or more entities
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Relationship set
- Set of all relationships of the same type (a.k.a relationship type)
- Entities participate in a relationship
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Visible object
Exist in the real world
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Invisible object
Does not exist in the real world, only conceptually (abstract)
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