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Data Model

Plan or blueprint for a database design. It's more generalized and abstract than design. It's easier to change than a design.

E-R Model

Set of concepts and graphical symbols that can be used to create conceptual schemas

Original ER

Peter Chen-1976

Information Engineering

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.

Entity Class

A collection of entities of a given type

Entity Instance

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

Relationship classes

Associations among entity classes

Relationship instances

Associations among entity instances


The number of entity classes in the relationship


Means count

One-to-One 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.

Minimum Cardinality

Zero if participation in the relationship is optional, 1 if the relationships is required or mandatory. (hash mark)

ER properities

Cannot indicate true minimum cardinalities on N:M relationships. Must use intersection table instead of true N:M model.

ID-Dependent Entities

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.

Weak entity

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

Subtype Entity

A special case of a super-type entity that contains specific attributes

Supertype entity

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

HAS-A Relationship

Strong entity relationships because each entity instance HAS A relationship with another entity instance.

IS-A Relationship

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.

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