ER Diagram In DBMS: Understanding The Entity Relationship Model

The ER diagram came onto the scene in the year 1971 when Peter Chen introduced it as a visual aid for database representation with ER model concepts. In this article, we will clear out important concepts related to the ER Model diagrams, such as their types, components, uses, and many more. Let us go ahead and read the article to learn more about the Entity Relationship diagram.

The Entity-Relationship Diagram (ER model) is a data model used in the database management system (DBMS) to represent the system data’s logical structure. It is similar to the blueprint of a database design that will eventually be implemented as a full database.

It provides a conceptual view of the data that aids developers in quickly figuring out the data system. It is important to create an ER diagram before the implementation of the database. It uses the entities, attributes, and relationships between them to visualize the structure of the database.

Let us understand the concept with the help of an example. We need to design a database for the school that consists of entities like students, whose attributes include their addresses, ID, name, age, grades, and more. Now, the address entity also comprises attributes such as City, street name, pin code, etc.

Also read: What Is a Database? Definition, Types, Uses, Advantages

Table of Contents

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Important Geometric Shapes With Their Meaning In ER Diagram

Let us understand the important components of the Entity Relationship Diagram.

Rectangle (Entity)

The rectangle represents the entity sets, the real-world objects used in the database. They are usually represented as rectangles in the relational database.

Ellipses (Attributes)

An ellipse is used to represent the attributes in an Entity Relationship Diagram. Attributes are the characteristics or properties of entities.

Diamonds (Relationship Sets)

Relationship sets represent associations between two or more entity sets. They represent the connections between the various entities as diamonds.

Lines (Connecting Attributes and Entity Sets)

Lines are used to connect the attributes and entities. They are used to represent the connections between attributes and the entity they relate to.

Double Ellipses (Multivalued Attributes)

Attributes that support multiple values are referred to as multivalued attributes. They are shown as two double ellipses joined by an entity set.

Dashed Ellipses (Derived Attributes)

Attributes that can be calculated from other attributes are referred to as derived attributes. They are shown using dashed ellipses.

Double Rectangles (Weak Entity Sets)

Entity sets without their own primary key are referred to as weak entity sets. It is based on the identifying connection to another powerful entity set. Weak entity sets are represented by double rectangles.

Double Lines

The double lines are the components of ER diagram which represents the total participation of the entity which means that each and every member of the entity sets participate in the connection.

Components of ER Diagram

Now let us discuss more about the Entity relationship diagram components and their role in the visualization of the database structure.

Entity Component

Entities are the fundamental concepts in the ER Diagram as it represent real-world objects, events, individuals, notions, etc. It is a component or object of data. This is represented in the ER Diagram by a rectangle.

For example: Let us take a real life example of a product and its categories. They will have a one to many relationship, as many products can belong to a single category.

Weak Entity

The entities that are dependent on the relationships of other entities and cannot be uniquely identified by their own attributes are called weak entities. They are represented by a double rectangle.

Let us take an example to understand a weak entity. Suppose there is a bank, and there are many accounts opened in the bank. You cannot identify a bank account uniquely without knowing the bank to which it belongs. Hence, the bank account is a weak entity.

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Attributes In ER Diagram

Attributes are used to describe the properties and characteristics of an entity in an ER Diagram. It is represented by an oval. There are mainly four major types of attributes.

Key Attribute

Key attributes are used to uniquely identify an entity in an entity set. It is represented by ovals as other attributes, but the text in it is underlined inside. It cannot be further decomposed into sub-attributes as it is already in its atomic form.

For example, let us suppose the above example ID is a key attribute.

Composite Attribute

Composite attributes are the combination formed with the help of many attributes.

In the diagram given below, address is composed of many attributes like state, city, pin code, country, etc.

Multivalued Attributes

These are the attributes that hold multiple values. Hence, they are known as multivalued attributes. They are represented by a double oval in the ER Diagram.

For example, there can be more than one phone number associated with a single person. Therefore, it is a multi-valued attribute.

Derived Attribute

The attributes that can be derived from the other entities of the ER Diagram is called Derived attributes. These types of attributes are represented by dotted lines.

For example, let us take an attribute like age that tells the age of a person. However, age can only be determined with the help of a DOB (Date of Birth) Attribute. Hence, it is what derived attributes are.

Relationships In ER Diagram

Relationships are the components of the ER Diagram that describe the connections or relationships between different entities in the diagram. It is represented by a Diamond shaped rhombus symbol.

For Example, let us take a student and teacher from a class. The relationship between the teacher and the student is that the teacher teaches the student.

Let us now have a look at the types of relationships in ER Diagram. There are mainly four types of relationships in an ER Diagram.

One-to-One Relationship

If there is only a single association between one instance of the entity and another instance of another entity, it is called a one-to-One Relationship in the ER Diagram.

Let us understand it with the help of a simple example, the relationship of marriage between a man and a woman. There can only be a one-to-one relationship between both of them, as they can only marry single women or men.

One-to-Many Relationship

Now, if only one instance of an entity on the left side is related to many other instances of the other entity on the right side, then it is called a one-to-many relationship.

For example, let us take two different entities scientists and inventions. Now they are related to each other as inventions. Now there is a one-to-many relationship between them, as one scientist can carry out many inventions.

Many-to-One Relationship

The relationship in which many entities on the left side of the ER Diagram are related to only one entity on the right side is called a many-to-one relationship.

For example, let us suppose there are many students who enroll in a course. Now here it is, Many-to-one relationships between the entities.

Many-to-Many Relationship

The relationship in which many entities on the left side of ER Diagram are related to many entities on the right side is called a Many-to-many relationship.

For example, let us take the relationship between students and the projects assigned. Now, many students can be assigned more than one project, and more than one can be assigned to more than one student.

Evolution Of Entity Relationship Diagram

ER Diagram is responsible for deciding how data will be organized and structured in a database. It serves as a framework that is used to create efficient database systems.

The Entity Relationship diagram was put forward by Peter Chen in the year 1971. It emerged as the major step in visualizing the database framework. The ER Diagram provides a visual representation or blueprint for the database to be implemented. It contains some rules and guidelines that are followed while making the ER Diagram.

ER Diagrams have evolved over time, and now they are a major part of Database Management systems (DBMS). It serves as the foundation for developing the logical structure, understanding rules, and ensuring data integrity. It represents the relationship between different entities along with their attributes.

How To Draw An Entity Relationship Diagram

Let us now look at the steps that must be followed while creating an ER Diagram.

You first need to identify the entities for the database you are creating. Entities are the objects in ER diagram, which is represented by an ellipse.
Now, you need to determine or find the relationship between the entities. The relationship is represented by a diamond shape in the center.
Now, you need to add or mention the properties of the given entity. Try to give simple names for easy understanding.
Now arrange them logically together, keep in mind that they should be arranged according to the type of relationship they follow.
After completing your ER diagram, review it properly and check for any errors that may have arisen in it. Check for duplicate or redundant connections and remove them.

Best Practices For Effective ER Diagram

Now we will get to know some of the best practices that we must consider while making an ER Diagram. Following these practices while making ER Diagrams will make your diagram more effective and easy to understand.

You must mention exactly the name that is suitable for that particular entity.
Remember that you need to avoid redundant and duplicate relationships and eliminate ambiguous ones.
Also, try not to mix one relationship with another in the same ER Diagram.
You can use colors at different places in the ER Diagram for better visualization.
Also, consider adding references and comments in the diagram for more information.

Also check: Fundamentals of Database Systems: DBMS Tutorial

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FAQs

How many types of relationships are there in an ER Diagram?

There are mainly four types of relationships in the Entity Relationship diagram.
- One-to-one Relationship
- One-to-Many Relationship
- Many-to-one Relationship
- Many-to-Many Relationship

What is the use of an ER Diagram in a Database Management System?

An entity Relationship Diagram is used to visualise the database in an effective way. It is like a blueprint for the database you are planning to implement. It uses different concepts, guidelines, and representations to make the database more effective.

What are some of the popular tools for creating ER Diagrams?

Some of the popular tools that can be used to make ER diagrams are Microsoft Visio, draw.io, Ludic hart, etc.

What are some of the attributes used in the ER diagram?

Some of the attributes used in the entity relationship diagrams
- Key attributes
- Composite attributes
- Multi-valued attributes
- Derived attributes

What is the use of a relationship in an ER diagram?

Relationships in the ER Diagram are used to represent the connections between entities. It is very important to show how two or more entities are connected to each other. A diamond shape symbol represents them.