Date post: | 05-Dec-2014 |
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Education |
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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.