Entity vs Entity Set vs Entity Type

The Entity-Relationship (ER) Model is one of the primary components of Database Management Systems and is important for designing the logical structure of databases. It helps define data and the relationship between the data entities, and it makes the system easier to visualize.

• ER Model is commonly used to design the structure of relational databases.
• Makes it easy to construct and visualize data hierarchies.
• Provides a clear framework for organizing database components.

Entity

An entity is anything real that has a defined and separate existence. It can be anything that can be described, named, or identified in separation from the rest of the items. This is vital in database design since entities are the fundamental components of information that are kept and controlled in a database. Each of these entities has attributes that help in describing the nature of the entity, distinguishing it from the other entities.

• An entity may be concrete, like a student, or a book, or abstract, like a holiday or a particular concept.
• An entity is represented by a set of attributes.
• In a particular relation in RDBMS, a particular record is called an entity.

Types of Entity:

• Tangible Entity: Entities that exist in the real world physically.
• Intangible Entity: Entities that exist only logically and have no physical existence.

Example : 

• A student with a particular roll number is an entity.
• A company with a particular registration number is an entity.

Entity Type

An entity type can be defined as a framework or a class of entities which are the focal point of this research. It is smaller to a schematic diagram, which defines the properties of the objects of this class. Entity types assist in classifying the same kind of entities into one group, which comes in use when dealing with their properties and relations in the database.

• The category of a particular entity in the relation in RDBMS is called the entity type.
• It is represented by the name of the table and its schema.

Example :

• A table named student in a university database.
• Employee table in a company database.

Entity Set

An entity set is a comprehensive representation of all entities of the same type at a specific time. The use of an entity set helps to aggregate and thus manage similar entities within databases. The entities of the entity-set have common attributes for each entity, but the values of those attributes are different. Entity sets are important components in database structure because they illustrate how information is organized and put away in tables.

• Entity sets need not be disjoint.
• The collection of all the entities in the relation of RDBMS is called an entity set.

Example :

• The collection of all the students from the student table.
• The collection of all the employees from the employee table.

Relation With Table :

Table Name : Student

• Entity : Each row (tuple) in a table represents one instance of an entity.
• Entity Type : Each entity belongs to the student type. Hence, the type of entity here is a student.
• Entity Set : The complete data set of all entities is called entity set. For the above table, the records with student id 1, 2, 3, 4 are the entity set.

Entity vs Entity Set vs Entity Type