ER Diagram in DBMS – Entity Relationship Model in DBMS

Entity Relationship Diagrams, better known as ER Diagrams, provide a clear and concise representation of entities, attributes, and relationships, assisting in the effective design and development of databases. Sound knowledge of statistics, exploratory data analysis, data preparation, machine learning techniques, and deep learning is a prerequisite for building ER models.

ER Diagram in DBMS  

Entity Relationship diagrams show the connections between entities in a database. It is the database’s structural architecture and serves as a framework for describing the relationships between the various pieces. The design and modeling of databases in software engineering and database management systems (DBMS) use the ER diagram heavily. 

What Does an ER Model in DBMS Mean?

An ER Model in DBMS is an Entity-connection Model, a high-level data model depicting the connection among the entity sets. It defines the entities and their associations, allowing developers to build the system’s conceptual design or logical architecture from a data viewpoint. ER model depicts a database structure using an ER diagram. 

ER diagrams can be translated into relational tables aiding in the rapid construction of databases. Database designers can use ER diagrams as a template to implement data, particularly in software applications. The Entity Connection Diagram illustrates the connection among entities in a database. ER diagrams assist one in describing words related to entity relationship modeling.

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Evolution of ER Models in DBMS

The Entity-Relationship (ER) model is a notional high-level data model diagram used to measure data needs and create effective databases. With the first presentation of ER diagrams as a general way for conceptual modeling in 1971, Peter Chen gave it its name. The idea is a best practice when building a database based on Charles Bachman’s data structure models. Relational databases’ reasoning and business rules are designed and constructed using ER diagrams and visual tools that duplicate the ER model.

Why Should One Use ER Diagrams in DBMS?

ER diagrams represent the data stored in a database and serve as the core design upon which a database is developed. Here are some reasons why ER diagrams are essential:

  • Conceptualization: ER diagrams assist you in understanding the database and let you know which fields need to be embedded for a given object. They offer a better grasp of the information to be kept in a database.
  • Reduced complexity: ER diagrams minimize complexity and allow database designers to develop databases quickly. They assist in methodically evaluating data and characterizing aspects using Entity-Relationship models.
  • Glimpse: ER diagrams show how all your tables should link and what fields will be on each table. They offer users a peek at the logical structure of the database.
  • Blueprint: Database designers can use ER diagrams as a blueprint for incorporating data in specific software applications. They are translatable into relational tables, allowing you to construct databases rapidly.
  • Documentation: ER diagrams can act as documentation to let people understand the essence of the database. They help examine existing databases to detect and fix flaws in logic or deployment.

Few ER Diagrams in DBMS Examples

Here are some examples of ER diagrams in DBMS:

  • For instance, in a school database, the Student will be an entity, having characteristics such as address, name, id, age, and so on. The address will be linked to additional data such as city, street name, pin code, etc.
  • A hospital’s ER diagram can include entities like Patients, Tests, and Doctors, each with its properties. This ER model’s connections are labeled “Works for” and “Treats.”

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ER Diagram Facts

Here are some critical facts about ER diagram:

  • Conceptual design: ER diagrams aid in defining a conceptual design for a database. They visually represent the database structure, including entities, properties, and relationships.
  • Entities, attributes, and relationships: ER diagrams are built on three essential concepts— entities, attributes, and relationships. Entities represent items, classes, individuals, or locations and are depicted as rectangles in the diagram. Attributes describe the characteristics of things and are characterized as ovals. Relationships define the relationships between entities and are displayed as diamond shapes.
  • Database modelling: Database design and modelling use ER diagrams extensively. They aid in constructing relational databases by describing the logic, business rules, and relationships between things. ER diagrams are a foundation for developing a database structure applicable to a relational database management system.
  • Visual representation: ER diagrams employ specialised symbols to represent entities, characteristics, and relationships. These symbols make the model distinctive and separate it from other diagrams. The diagram gives a graphical depiction of how entities and their connections are connected throughout the system. 
  • Database integration: Integrating an ER model with an existing database might be problematic owing to various architectures. However, ER diagrams can represent and interact with databases, helping to establish needs and build the database structure.

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ER Diagram Symbols

The ER diagrams use specific symbols to represent these elements. Here are the symbols commonly used:

  • Rectangles: Represent entity types.
  • Ellipses: Represent attributes.
  • Diamonds: Represent relationship types.
  • Lines: Link attributes to entity types and these with other relationship types.
  • Primary key: Underlines the attributes.
  • Double Ellipses: Stand for multi-valued attributes.

ER Diagram Components

ER diagrams are composed of entities, attributes, and relationships:


Entities are often displayed in a rectangle and can be represented by things, humans, concepts, or events that include data. An entity can be any item, class, person, or location. The entity relationship model in DBMS allows users to quickly identify and understand the connections between various entities, helping develop accurate and reliable database systems.

There are two categories of entity type in DBMS— strong entities and weak entities. Strong entities are symbolically represented by a rectangle encompassing their name, whereas a double rectangle characterises weak entities. 


Attributes are qualities or properties of an entity and are represented as ellipses in an ER diagram. Attributes might be basic, composite, or multi-valued.


Relationships demonstrate how two or more things interact and are displayed as labels on the lines linking the items. Relationships can be one-to-one, one-to-many, or many-to-many.

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Drawing an ER Diagram

Follow these general steps to draw an ER diagram:

  1. Identify the entities: Determine the entities you represent in the system or database. Entities are often nouns, such as automobile, bank, student, or product.
  2. Determine the relationships: Identify the connections between the entities. Connect the items using lines and put a diamond in the centre to describe the relationship. For example, if you have entities like “Student,” “Course,” and “Professor,” you can connect them to show the relationship between a student registering for a course taught by a professor.
  3. Add attributes: Add attributes to the entities. Attributes are the specific features or properties of an entity. Give meaningful names to the qualities for easy identification. For example, for the “Student” object, you can have characteristics like “student ID,” “name,” and “major”.
  4. Organise the diagram: Logically arrange the entities, connections, and qualities in an ordered manner to facilitate recognition.
  5. Review and refine: Review your ER diagram to verify correctness and clarity. Remove any ambiguous, duplicated, or redundant connections between entities.

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Developing Effective ER Diagrams: Best Practices

Here are some best practices for developing practical ER diagrams:

  • Provide exact and suitable names: Give each item, attribute, and relationship in the diagram a precise and acceptable term.
  • Eliminate ambiguous, redundant, or superfluous relationships: Eliminate duplicate entities or relationships, and eliminate vague or needless links between entities.
  • Avoid tying a connection to another relationship: Never tie a relationship to another.
  • Make efficient use of colours: Use colours to categorize comparable things or to highlight significant sections in your diagrams.
  • Follow a name convention: Follow a consistent naming convention for entities, characteristics, and relationships.
  • Avoid overlapping references: Avoid overlapping references between things.
  • Add comments: Add notes to your diagrams to offer further context and information.

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Wrapping Up

The ER diagrams capture user demands by offering a visual view of the database structure. They are crucial in the database design process and help stakeholders interact successfully. 

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Frequently Asked Questions 

What are relationships in an ER diagram, and how are they represented?

The relationships in an Entity-Relationship (ER) diagram show how different entities are linked. Diamond-shaped symbols represent links, and lines connect them to the linked elements. The lines linking the entities to the diamond symbol represent their cardinality and the nature of their connections.

What is cardinality, and how is it represented in an ER diagram in DBMS?

Cardinality measures how many occurrences of one object can be linked to another. The minimum and maximum number of occurrences of an entity that can be connected to another entity, respectively, are represented by the symbols 1 and N in an ER diagram. If two entities have a 1:N cardinality, for example, only one instance of the first can be connected to each instance of the second. Numerous instances of the second item can be connected to a single example of the first thing.

Can an ER diagram be converted into a physical database schema?

Yes, an ER diagram can be turned into a real-world database setup. The relational model is the logical level of database design, whereas the ER diagram represents the conceptual level. Converting an ER diagram to a relational schema diagram in DBMS requires determining the primary key, translating each entity type into a table, and turning each attribute into a column in the database.

What are some popular software tools for creating and visualising ER diagrams?

Some typical software applications for constructing and visualising ER diagrams include Lucidchart, Microsoft Visio, and

What are the common attributes associated with an entity type?

Common attributes are simple, composite, single-valued, multi-valued, derived, and complex. Simple attributes can be broken down into smaller components, whereas composite attributes comprise several smaller attributes. Non-key attributes are not unique, main, secondary, or foreign keys, whereas key attributes uniquely identify an object.

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