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ER Model 1

Entity Types

Relationship Types

Attributes

Strong & weak entity types

Attributes on relationship

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Entity Types

Definition

An entity type is a real-world item orconcept that exists on its own.

Example

Book and customer are some of the entity.

Class Student

Entities tendto be nouns

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Relationship Types

Definition A relationship type is a set of

associations among entity types

Example Class and student are two entity types

which has a relationship that can be

associate with. Class consists of students.

Student

Class ConsistOf

Relationships tendto be verbs

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Degree of relationship

The degree of a relationship type is the

number of entity types that can beassociate with.

Two is called binaryrelationship type

Three is called ternaryrelationship type Example

Student buy books from bookshop

BookShopStudent Buy

Book Ternary relationship type

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Attributes

Definition An attribute of an entity is a particular

property that describes the entity.

Attribute Domain Refer to the value of the attribute

Example

Book

Author

Attribute

Attribute Domain

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Simple Attribute

A simple attribute is one component that is atomic.

Key An attribute or set of attributes that uniquely identifies a

particular entity is a key

Example

Composite Attribute

A composite attribute has multiple components, each of

which is atomic or composite.

Example

BookISBN

BookAuthor

Last

Name

FirstName

Key

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Single-Valued Attribute & Multi-Valued Attribute

For a particular entity, single-valued attribute only can

holds one value but multi-valued attribute can hold morethan one value.

Example

Hobbies Student

RegisterNo

Student

Single-Value Attribute

Multi-Value Attribute

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Strong & weak entity types

An entity type is strong if its existencedoes not depend on some other entitytype. Otherwise, the entity type is

weak. Example

Class is a strong entity type while student

is a weak entity type.

StudentClass ConsistOf

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Attributes on relationship

The attributes on the relationship type,which connect the entities, unable toassociate with them.

Example

BookSupplier deliver

DeliveryDate

DeliveryCondition

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References

http://en.wikipedia.org/wiki/Entity-relationship_model

http://wofford-

ecs.org/dataandvisualization/ermodel/material.htm

http://www.inf.unibz.it/~franconi/teachi

ng/2000/ct481/er-modelling/

http://en.wikipedia.org/wiki/Entity-relationship_modelhttp://en.wikipedia.org/wiki/Entity-relationship_modelhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://www.inf.unibz.it/~franconi/teaching/2000/ct481/er-modelling/http://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://wofford-ecs.org/dataandvisualization/ermodel/material.htmhttp://en.wikipedia.org/wiki/Entity-relationship_modelhttp://en.wikipedia.org/wiki/Entity-relationship_modelhttp://en.wikipedia.org/wiki/Entity-relationship_model