Peter Chen developed entity-relationship (ER) diagrams in 1976 to model databases. ER diagrams use entities (objects), attributes (data about entities), and relationships (connections between entities) to represent the structure and semantics of data. Developing an ER diagram helps database designers and analysts better understand the information to be stored in a database by modeling the entities, attributes, and relationships visually.

1. History of ER (entity
relationship) Diagram:
Peter Chen developed ERDs in 1976. Since then
Charles Bachman and James Martin have added
some slight refinements to the basic ERD
principles.

2. ER (entity relationship)
Diagram:
ER Model is represented by means of an ER
diagram. Any object, for example, entities, attributes
of an entity, relationship sets, and attributes of
relationship sets, can be represented with the help of
an ER diagram.

3. Why we design ER diagrams?

4. Why we design ER
diagrams?
The software developer/analyst or database
designer/analyst gains a better understanding of
the information to be contained in the database
through the process of constructing the ERD.
The ERD serves as a documenting tool.

5. ER (entity relationship)
Diagram:
There are three basic elements in ER-Diagrams:
 Entities are the "things" for which we want to
store information. An entity is a person, place,
thing or event.
 Attributes are the data we want to collect for an
entity.
 Relationships describe the relations between
the entities.

6. Symbols of ERD

7. Entity
Any object having attributes and their values
from real word is entity. Entities are represented
by means of rectangles. Rectangles are named
with the entity set they represent.

8. How to represent Entity

9. Relationship
Relationships are represented by diamond-shaped
box. Name of the relationship is written inside the
diamond-box. All the entities (rectangles)
participating in a relationship, are connected to it by
a line.

10. How to represent Relationship

11. Attribute
Attributes are the properties of entities. Attributes
are represented by means of ellipses. Every
ellipse represents one attribute and is directly
connected to its entity (rectangle).

12. How to represent Attribute

13. Composite attributes
If the attributes are composite, they are further
divided in a tree like structure. Every node is then
connected to its attribute. That is, composite
attributes are represented by ellipses that are
connected with an ellipse.

14. Composite Attributes

15. Derived attributes
Derived attributes are depicted by dashed
ellipse.

16. Derived attributes

17. Multivalued attributes
Multivalued are depicted by double ellipse.

18. Multivalued attributes

19. Notations of ER diagram

20. One to One Relationship
For example, if each customer in a database is
associated with one mailing address.

21. One to One Relationship

22. One to many Relationship
For example, a single customer might place an
order for multiple products. The customer is
associated with multiple entities, but all those
entities have a single connection back to the
same customer.

23. One to many Relationship

24. Many to many Relationship
For example, at a company where all call center
agents work with multiple customers, each agent is
associated with multiple customers, and multiple
customers might also be associated with multiple
agents.

25. Many to many Relationship

26. The phase in which we
need to design an ER
diagram
In Designing phase we need to design ERDs.

27. ER diagram of Internet Sales
Model

28. Any Questions ??

29. Thank you for your attention!