In - House BDA Introduction ER Model.pdf

ER MODEL

1. Entity Relationship Model (ER-Model)
An Entity–relationship model (ER model) describes the
structure of a database with the help of a diagram,
which is known as Entity Relationship Diagram (ER
Diagram). It consists of a collection of basic objects,
called entities(which is distinguishable from other
objects) and of relationships among these objects.

2. Entity Relationship Model (ER-Model)
Components of ER Model
•Entity
•Attribute
•Relationship

3. Entity Relationship Model (ER-Model)

4. Entity Relationship Model (ER-Model)

5. Entity Relationship Model (ER-Model)
1. Entity
An entity is an object or component of data. An entity is
represented as rectangle in an ER diagram.

6. Entity Relationship Model (ER-Model)
Weak Entity:
An entity that cannot be uniquely identified by its own
attributes and relies on the relationship with other entity is
called weak entity. The weak entity is represented by a
double rectangle.

7. Entity Relationship Model (ER-Model)
2. Attribute
An attribute describes the property of an entity. An attribute
is represented as Oval in an ER diagram. There are four types
of attributes

8. Entity Relationship Model (ER-Model)
a. Key attribute:
A key attribute can uniquely identify an entity from an entity
set. Key attribute is represented by oval same as other
attributes however the text of key attribute is underlined.

9. Entity Relationship Model (ER-Model)
b. Composite attribute: An attribute that is a combination of
other attributes is known as composite attribute.

10. Entity Relationship Model (ER-Model)
c. Multivalued attribute:
An attribute that can hold multiple values is known as
multivalued attribute. It is represented with double ovals in
an ER Diagram.

11. Entity Relationship Model (ER-Model)
d. Derived attribute:
A derived attribute is one whose value is dynamic and
derived from another attribute. It is represented by dashed
oval in an ER Diagram.

12. Entity Relationship Model (ER-Model)
3. Relationship
Cardinality: Defines the numerical attributes of the relationship
between two entities or entity sets.
A relationship is represented by diamond shape in ER diagram, it
shows the relationship among entities.

13. Entity Relationship Model (ER-Model)
a. One to One Relationship
When a single instance of an entity is associated with a single
instance of another entity then it is called one to one relationship.

14. Entity Relationship Model (ER-Model)
b. One to Many Relationship
When a single instance of an entity is associated with more than
one instances of another entity then it is called one to many
relationship.

15. Entity Relationship Model (ER-Model)
c. Many to One Relationship
When more than one instances of an entity is associated with a
single instance of another entity then it is called many to one
relationship.

16. Entity Relationship Model (ER-Model)
d. Many to Many Relationship
When more than one instances of an entity is associated with more
than one instances of another entity then it is called many to many
relationship.

17. Entity Relationship Model (ER-Model)
Participation Constraints in Relationship
Total Participation
Partial Participation

18. Entity Relationship Model (ER-Model)
Steps to Create an ERD (E-R Diagram)
1.Entity Identification
2.Relationship Identification
3.Cardinality Identification
4.Identify Attributes
5.Create ERD

19. Entity Relationship Model (ER-Model)
Entity Identification
•Student
•Course
•Professor

20. Entity Relationship Model (ER-Model)
Relationship Identification
•The student is assigned a course
•Professor delivers a course

21. Entity Relationship Model (ER-Model)
Cardinality Identification
•A student can be assigned multiple courses
•A Professor can deliver only one course

22. Entity Relationship Model (ER-Model)
Participation of Entities
•Total Participation
•Partial Participation

23. Entity Relationship Model (ER-Model)
Identify Attributes
•You need to study the files, forms, reports, data currently
maintained by the organization to identify attributes.