What are ER diagrams in DBMS? A complete Guide for you to Follow

This guide is a comprehensive tour of the ER diagrams and their components. You will learn to create these diagrams using entities, attributes, and relationships.

what are the main components of an ER diagram

ER diagrams are used when you need some sort of a database. These diagrams make reading all the components that make the database run ideally easier. They show all the labeling of attributes taking part in the database, and developers get a quick idea about the storage capacity needed for each point or entity.

An ER diagram clears all the doubts and ambiguities if you want anyone new to learn about your model. It is only possible to understand a model with a diagram.

In this article, you will find out how important ER diagrams are in DBMS and how they are helpful for developers to understand the needs of business owners.

In this article
  1. What is an ER Diagram?
  2. Components of an ER Diagram
  3. Why Use ER Diagrams in DBMS?
  4. ER Diagrams Symbols & Notations
  5. How to Draw an ER Diagram?
  6. Examples of ER Diagrams
  7. Conclusion

Part 1. What is an ER Diagram?

An ER (Entity-Relationship) diagram is a flowchart that illustrates the entities and the relationship among them in any model. Software engineers use ER diagrams to design or debug relational databases. These models are best suited for research, data collection, and educational purposes.

An ER diagram in a DBMS (Database Management system) is vital in designing a database for multiple businesses. It is a structural design of a system that engineers use to demonstrate the entities and their relationships in a database. Developers use these structures to form a database. So, it is crucial to create these diagrams before designing a database.

History of ER Models

ER Models were first introduced by Peter Chen back in 1971. The purpose of these diagrams was to understand and create a uniform convention that could help design a database. This was one of the finest finds, as many other models were introduced to design databases, but none worked well.

Charles Bachman's structural diagram model helped Peter find something new, and he was able to introduce ER diagrams. Charles worked on database models in the 1960's. Peter used Charles's work and derived new forms of his diagrams known as ER diagrams.

There were few advancements in Peter Chen's work in the early 80s, but his work was considered the best even after those inventions.

Part 2. Components of an ER Diagram

There are three essential components of an ER Diagram.

  1. Entities
  2. Attributes
  3. Relationships

The image below best describes the components of an ER Diagram.

what are the main components of an ER diagram


An entity could be a living or non-living component in these diagrams. Entities are the main components in any ER diagram. The sub-category of an entity is called a weak entity. A doubled rectangular shape denotes a fragile entity.


Attributes are the properties of an entity. For example, a worker working in an organization has his employee number, name, age, etc. There are further four attributes: key attribute, composite attribute, multivalued attribute, and derived attribute.

  • Key attribute: It is identified by the entity set, and an underline is placed while labeling it.
  • Composite attribute: It has other attributes as well that describe its properties.
  • Multivalued attribute: This attribute could have more than one specific attribute. For example, a person could have more than one phone number, so this type of attribute would be a multivalued attribute.
  • Derived attribute: The type of attribute whose value could easily be determined by the other attributes. For example, a person's age is a derived attribute as age could be determined by the other attribute named date of birth.


The connection between the two entities is called a relationship in the ER diagram. Relationships are of four types: one-to-one, one-to-many, many-to-one, and many-to-many.

The picture below shows the best representation of the components of the ER diagram.

Part 3. Why Use ER Diagrams in DBMS?

ER diagrams are used to build database programs for the storage of information for all the entities in a system. ER diagrams are used to reduce the complexity of the system. They better understand the system and allow software developers to connect the fields to a particular entity.

It allows the developers to understand the database size and space needed to run it better, as a lot of information is stored in those entities. From a user's point of view, an ER diagram allows them to conceptualize the logical structure of the system. Business owners use the ER diagram to let engineers know about their needs.

These diagrams offer liberty to engineers when they need any change in the system. If they want an entity to be added to the system, an ER diagram helps them see if they can adjust the model.

Part 4. ER Diagrams Symbols & Notations

Rectangle Shape

Rectangular shapes are used to denote entities in the system. For example, an employee works in a company. Both workers and the company are entities, and their relationship is a job.

representation of entities in ER diagram

Double Regular Shape

Double rectangular shapes are used to denote weak entities in the system. Weak entities are not defined by their own properties or attributes.

how to represent a weak entity


The oval shape is used to denote the attribute in the system.

how to represent attributes in the ER diagram

Double Eclipse Shapes

These shapes are used to denote weak attributes in the system.

how to represent a weak attribute in an ER diagram

Dotted Ellipse

An attribute that can easily be derived from other attributes is called a derived attribute. A dotted eclipse is used to denote this attribute.

how to represent derived attribute

Diamond Shape

A diamond shape denotes a relationship between the entities.

how to represent a relationship in an ER diagram

Part 5. How to Draw an ER Diagram?

Making an ER diagram is not so complicated. Let's take a look at them.

  1. Choose a suitable tool. Some popular options are Draw.io, Visio, and SmartDraw. If you are a beginner, consider trying EdrawMax, which is known for its simplicity and user-friendly interface.

  1. Draw all the entities in the diagram. Use a rectangle shape to denote them in the diagram. Fill in the names of the entities properly.
  2. The next step is to identify the relationships between entities. Use a diamond shape to form that relationship. Remember, two relationships are never connected in an ER diagram.
  3. Now, start connecting the attributes to each entity through eclipse shapes. Name them according to the information.
  4. Make sure all the components are correctly placed in the diagram with proper labeling.
  5. Use different colors for entities if you want to. It can help anyone understand the main component in the diagram.
  6. Make sure one entity is used only once in the diagram. Any entity in the diagram can not be used twice.

Part 6. Examples of ER Diagrams

Hospital Management ER diagram in DBMS

Here is a hospital management ER diagram in DBMS. This diagram fully elaborates the model where patients come to the hospital for checkups. Full details of the doctor, including his name, qualifications, and specialization, are added as attributes. Doctor and patient are the two main entities.

Treatment is the relationship between these two entities, i.e., doctor and patient. The third entity usually includes the tests advised by the doctor.

How to draw an ER diagram for a hospital management system

Student Management ER Diagram in DBMS

The image below shows how to draw an ER diagram for the student management system. A teacher teaches the students studying in the college having attributes: name, salary, and address. Meanwhile, the students have attributes like GPA and the department in which they are studying.

The third entity used in this ER diagram is the courses that students choose. The teacher, the first entity, teaches those courses. Student-management-system and finally rating their grades based on marks.

how to draw an ER diagram for a student management system


The conceptual design of any database is drawn through an ER Diagram. They are of great importance due to their simple methodology. This methodology makes it easier for users and designers to understand the system. However, things get a little easier when you find some readymade templates. You don't need to draw your shapes in the first place.

The template provides you the liberty to choose the components. You only need to connect those components to create a diagram. Edrawmind offers plenty of templates, making life easier for the users.

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Edraw Team
Edraw Team Apr 03, 24
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