E-R Diagram

Presented by:

Fatiha Rashid

Javeria Rafeeq

Logical representation of data in an organization.

Views the entire system as a collection of entities related to one another.

Introduced by peter chen in 1976.

Introduction:

Advantages of E-R Model:

CONCEPTUAL SIMPLICITY:

VISUAL REPRESENTATION:

EFFECTIVE COMMUNICATION TOOL:

Elements of E-R Model:

1: Entities

2: Attributes

3: Relationships

Entities:An Entity is a Person,Place,Thing or Event for which data is collected and maintained.

•Represented by a rectangle

Entity name symbol

Entity type / Entity class:A set of entities with same attributes

Exmaple: Student entity class is a set of All students.

Book entity type is for all Books etc.

Entity instance

A member of an entity class is known as entity instance .

Also known as entity occurrence.

Entity Class

Entity instance

Entity class

Entity instance

ATTRIBUTES:

** The characteristics of an entity are called attributes or properties.

Example: Name, address,Class and Email of a students are his attributes.

Attribute name

Symbol

Attribute Domain:

*A set of possible values for an attribute

*All atributes have domain

Example : The domain for Grade point average (GPA) can be from 0 to 4.

Similarly, domain for Gender attribute can be Either male or female.

Relationships:*A logical connection between different enities.* Established on the basis of interaction between these entities.

Participents: entities participating In a relationship are called participents.

Relationship nameSymbol

Doctor treats Patient

Teacher teaches students

Total Relationship:

Partial relationship:

If all entities of that entity set may be participant in the relationship.Example: In supplier_part relationship,the relationship is total if every part is supplied by a supplier.

If some of the entities of that entity set may be participant in the relationship.Example: If certain parts are available without a supplier.

Types of Attributes

1: Simple 2: composite 3: single valued4: multi-valued 5: stored6: derived7: identifiers

SIMPLE ATTRIBUTE/ ATOMIC ATTRIBUTE:

*Cannot be subdivided into smaller components.

PERSON

GENDER

Composite attribute:*Can be divided into smaller components.

EMPLOYEE

ADDRESS

streetcity

country

Single-valued Attributes:Contain single valued value.

Employee

Gender

Multi-valued Attributes:

Contain two or more values.

person

namecity hobies

Stored Attributes:*Stored in a database.

Derived attributes:*Not stored in database but derived from another value.

IDENTIFIERS:Identifies an entity instance among other instances In entity class.

ENTITIES:

**WEEK & STRONG ENTITIE

***ASSOCIATIVE ENTITIES

Weak entity& strong entity week entity Can exist only if any other entity exist, also called child ,dependent .Strong entity Can exist without depending

upon the existance of another entity .

PERSON HAS CHILDCHILD

Owner/ identifying owner: entity on which the weak entity depends.Example

ASSOCATIVE ENTITIES:

Type of entity that associates the instances of one or many entity type with one another.

Degree of relationships:

•The number of entities in a relationship .

•Types:•1: unary relationship•2: binary relationship•3: ternary relationship

Unary relationship:

Binary relationships:Exist between the instances of two entity types.Types:1: one-to-one

2:one-to-many

3:many –to-many

One to one:

One to many:

Many to many:

Ternary relationships:

Cardinality constraints:The maximum number of relationships.

*Circle means zero

*Line means………..one

*Crow’s foot symbol means….many

Past paper 2010

employee

department

jobs

equipment

suppliers project

name DOB

Phone no

Project no Project name

Project cost duration

name AddressDate of last meeting

number

To conclude E-R diagram is a graphical representation

Of data in an organization.It includes entities,attributes

and relationships.

Conclusion:

We hope you liked it.