Presentation about Entity Relationship Diagram (ERD)

1. ENTITY RELATIONSHIP
DIAGRAM (ERD)

2. GROUP MEMBERS
 MD. Shahariar Alam (162-15-8113)
 Avijit Roy (162-15-7898)
 MD. Monir Hossain (162-15-8033)
 MD. Muin Mahmud (162-15-7983)
 MD. Hasanuzzaman (162-15-8025)
 Amiya Adhikary (162-15-7980)

3. WHAT IS AN ERD & WHY IT IS USED?
Database systems are often modeled using an Entity Relationship Diagram
(ERD) as the "blueprint" from which the actual data is stored.
The ERD is used to communicate
the logical structure of the
database to users.

4. Entity: An entity can be a real-world object, either animate or inanimate, that can
be easily identifiable.
Example:
Person Place Object
Entity Set: An entity set is a collection of similar types of entities. An entity set
may contain entities with attribute sharing similar values.

5. ATTRIBUTES
Entities are represented by means of their properties, called attributes. All
attributes have values. Example : Student :- Name, Class, Age
Types ofAttributes:
Simple attribute: Simple attributes are atomic values, which cannot be divided
further.
Example:The entities like age, marital status cannot be subdivided and are simple
attributes.
 Composite attribute: A composite attribute is one that is composed of smaller
parts.
Example: Name, Date of Birth.

6. Derived attribute: A derived attribute is an attribute whose value is calculated
(derived) from other attributes.
Example: Age, it can be calculated from date of birth.
Single-value attribute: Single-value attributes contain single value.
Example: Gender, Date of Birth.
Multi-value attribute: Multi-value attributes may contain more than one values.
Example: Phone number, Email.

7. RELATIONSHIP
Associations between instances of one or more entity types that is of
Interest.

8. Degree of Relationship
Binary Relationship: between the instances of two entity types.
Teacher SubjectTeaches

9. Ternary Relationship:Among the instances of three entity types.
Teacher StudentTeaches
Subject

10. CARDINALITY
Cardinality defines the number of entities in one entity set, which can be
associated with the number of entities of other set via relationship set.
 One to one
 One to many
 Many to one
 Many to many

11. KEY CONSTRAINTS
 Super Key
 Candidate Key
 Primary Key
 Foreign Key
Attribute
Primary Key
Candidate KeySuper Key

12. GENERAL STEPS TO CREATE AN ERD
 Identify the entities
 Identify the relation between entities
 Identify the Cardinality constraint
 Identify the entity's attributes
 Draw the ERD

13. A SIMPLE EXAMPLE
A company has several departments. Each department has a
supervisor and at least one employee. Every supervisor has
only one department under him. Employees must be
assigned to at least one, but possibly more departments.At
least one employee is assigned to a project, but an employee
may be on vacation and not assigned to any projects.The
important data fields are the names of the departments,
projects, supervisors and employees. Supervisors and
Employees also have ID, Email, Phone and a unique project
number.

14. Supervisor
S_ID
Name
Email
Phone
Department_name
Project
Project_Number
Project_Name
Employee
E_ID
Name
Email
Phone
Project_Number
Department
Department_Name
Run
by
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gned
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11
1…*1…*
0…* 1
ER Diagram

15. RELATIONAL SCHEMA
Department(Department_Name)
Supervisor(S_ID, Name, Email, Phone, Department_Name)
Employee(E_ID, Name, Email, Phone, Project_Number)
Project(Project_Number, Project_Name)