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Database Design-Chapter 5
Plan or blueprint for a database design. It's more generalized and abstract than design. It's easier to change than a design.
Set of concepts and graphical symbols that can be used to create conceptual schemas
James Martin, 1990, it uses crow's foot notation, it's easier to understand
National standard developed by the National Institute of Standards and Technology.
UML-Unified Modeling Language
The Object Management Group; it supports object-oriented methodology.
A collection of entities of a given type
The occurrence of a particular entity
Originally shown as ellipses. Now they are shown in rectangular form.
Attributes that name, or identify entity instances. The Consists of one or more of the entity's attributes
Associations among entity classes
Associations among entity instances
The number of entity classes in the relationship
The entity on the one side of the relationship is called the parent entity . The entity on the child side of the relationship is called the child entity.
Zero if participation in the relationship is optional, 1 if the relationships is required or mandatory. (hash mark)
Cannot indicate true minimum cardinalities on N:M relationships. Must use intersection table instead of true N:M model.
An entity whose identifier includes the identifier of another entity.
ID-Dependent Entities Properties
Minimum cardinality to the parent is always one (required.) A solid line is used to identify ID-dependent entities.
An entity whose existence depends upon another entity
Weak entity properties
All ID-Dependent entities are weak, but not all weak entities are ID-dependent. Indicated by non-identifying relationship
A special case of a super-type entity that contains specific attributes
Contains all common attributes.
One supetype relates to at most one subtype. Ex. Employee can be a manager or DB Admin, but not both.
One supertype can relate to one or more subtypes. Ex. Employee can be admin or Manager
Strong entity relationships because each entity instance HAS A relationship with another entity instance.
Supertypes/Subtypes relationships are called IS-A relationships because a subtype IS A supertype.
Data model process 1
Analyze the business documents
Data model process 2
Identify all potential entities, including identifier and attributes for each entity
Data model process 3
Specify relationships (Both max & Min cardinality
Data model process 4
Create the E-R Model
Data model process 5
Validate the model by showing the designed forms and reports to customers.