Entity relationship (ER) models are based on the real-world entities and their relationships. It is easy for the developers to understand the system by simply looking at the ER diagram. ER models are normally represented by ER-diagrams.
ER diagram basically having three components:
Entities − It is a real-world thing which can be a person, place, or even a concept. For Example: Department, Admin, Courses, Teachers, Students, Building, etc are some of the entities of a School Management System.
Attributes − An entity which contains a real-world property called an attribute. For Example: The entity employee has the property like employee id, salary, age, etc.
Relationship − Relationship tells how two attributes are related. For Example: Employee works for a department.
An entity has a real-world property called attribute and these attributes are defined by a set of values called domain.
In a university,
A student is an entity,
University is the database,
Name and age and sex are the attributes.
The relationships among entities define the logical association between entities.
Given below is another example of ER:
In the above example,
Entities − Employee and Department.
Employee − Name, id, Age, Salary
Department − Dept_id, Dept_name
The two entities are connected using the relationship. Here, each employee works for a department.
The features of ER Model are as follows −
Graphical Representation is Better Understanding − It is easy and simple to understand so it can be used by the developers to communicate with the stakeholders.
ER Diagram − ER diagrams are used as a visual tool for representing the model.
Database Design − This model helps the database designers to build the database.
The advantages of ER are as follows −
The ER model is easy to build.
This model is widely used by database designers for communicating their ideas.
This model can easily convert to any other model like network model, hierarchical model etc.
It is integrated with the dominant relational model.
The disadvantages of ER are as follows −
There is no industry standard for developing an ER model.
Information might be lost or hidden in the ER model.
There is no Data Manipulation Language (DML).
There is limited relationship representation.