An entity relationship diagram (ERD) shows the relationships of entity sets stored in a database. An entity in this context is a component of data. In other words,

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Dr. Mohammed Kassim Page 37
Entity Relationship Diagram
Entity Relationship Diagram
An entity relationship diagram (ERD) shows the relationships of entity sets
stored in a database. An entity in this context is a component of data. In other
words, ER diagrams illustrate the logical structure of system and databases.
ER diagrams is modeling tool used to depict graphically a system and database
design before it is actually implemented.
It has three basic components:
 Entity

Is a real-world object unique from other objects. An entity can be a
physical object like employee, student, faculty, customer etc. Or it could
also be conceptual or abstract like transaction, order, course, subjects
etc. It is normally represented by a rectangle shape.







 Relationship

Is a way of relating one entity to another. Entities can therefore participate
in a relationship. it is commonly thought as a verb connecting the entities
or nouns. It is normally represented by a diamond shape.

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Entity Relationship Diagram
Types of Relationship:
Example – Relationships:
A departments in university consists of a number of courses. A number of
modules make up each course. Students enroll in a particular course and take
modules towards the completion of that course. Each module is taught by a
lecturer from the appropriate department, and each lecturer has a group of
students.
Entities: Department, Course, Module, Lecturer, Student

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Entity Relationship Diagram
 Attributes
The characteristic or basic fact or field of an Entity or Relationship.
for example a Student entity could have the following attributes
(ID Number, Last Name, First Name, Address, Birth Date). A relationship
could also have an attribute for example an Entity name Student enrolls
(relationship) to a Course/Program.

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Entity Relationship Diagram
Example of Attributes:
Entities: Program, Student , Faculty
Attributes: Program (Program ID, Name, Chairperson, Enrollment Date) –
Student (IDNo, Lastname, Firstname, Gender, Address, Birth Date, Email) –
Faculty (IDNo, Name, Chairperson, specialization)