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ER-Diagram Model and Its Elements / Components in DBMS

DBMS | ER-Diagram Model: In this tutorial, we will learn about the ER-Diagram model, and its basic elements. By Prerana Jain Last updated : May 27, 2023

What is an ER-Diagram Model in DBMS?

ER Diagram stands for "Entity Relationship Diagram" which helps us to understand the relation of different entities (objects or tables) in the database and explains the structure of databases. It is a part of the software that how we are going to design our database.

ER Diagram was introduced by Dr. Peter Chen in 1976. It is a database model based on the perception of the real world that consists of a Collection of basic objects and the relationship between them. It is a non-technical method that is free from ambiguity. It provides a standard and logical way of organizing and visualizing data. This model maps real-world things into a conceptual schema. The conceptual schema is a concise description of data requirements. These concepts do not include implementation details and are easier to understand and commercialize for non-technical users.

Basic Elements of ER Diagram

In an ER-Diagram model, there are three basic elements: Entity/Entity Set, Attributes, and Relationships. Other elements based on the main elements are: Weak entity, Strong entity, Simple attribute, Key attribute, Composite attribute, Derived attribute, and Multivalued attribute. Here, we will discuss the basic elements.

1. Entity/Entity Set

An object is called entity if it can be identified in a group of objects based on the values of the attribute it processes.

Entity can be of two types: Tangible and Intangible.

1.1. Tangible Entity

Tangible are those type of entity which exist Physical existence in the nature.

Example: A Bank locker, person, car etc.

1.2. Intangible Entity

Intangible are those type of entity which exist Logically in the nature.

Example: A Bank account, Job Company etc.

Collection of similar type of entity is called entity set. In ER Diagram entity is a instance and it is represented as a rectangular box while in a relational model it is represented by independent tables. Entity set is associated with the set of attributes.

2. Attributes

Attributes are the properties on which we can define entities. In ER Diagram they are represented by an oval or ellipse while in a relational model they are represented by independent column.

Attributes can be of three types: Composite and single(Atomic), Single-valued and Multi-valued Attributes, and Stored and Derived Attributes.

2.1. Composite and single(Atomic) Attributes

The attributes which can be further divided into smaller attribute then it is called composite attribute.

Example: Address can be divided into city, state,country.

The attributes which cannot be further divided are called simple or atomic attributes.

Example: Age

In an E R Diagram composite attribute represented when an oval is connected to an oval.

2.2. Single-valued and Multi-valued Attributes

Attributes which having a single value at any instant of time is called single valued attribute.

Example: Gender

Attributes is to be multivalued if it can take more than one values at a time.

Example: Phone no, Address no.

2.3. Stored and Derived Attributes

Attribute is said to be stored if its value is permanently stored in the database.

Example: Date of birth.

The Attributes whose value is derived or calculated at run time the it is called derived attribute.

Example: Age can be derived from the date of birth.

3. Relationships

Relation specify that how a entity of a entity set is related to the entity of another set. In a ER Diagram it is represented by a diamond. Every relationship will have a unique name.

Every relationship will have a degree which means no of entity set participating.