Entity in DBMS

Question

Can anyone explain the concepts of entity and entity sets in detail?

Answer 1

@vishnu777

Entity An entity is a real-world thing which can be distinctly identified like a person, place or a concept. It is an object which is distinguishable from others.

If we cannot distinguish it from others then it is an object but not an entity.

An entity can be of two types:

Tangible Entity: Tangible Entities are those entities which exist in the real world physically.

Example: Person, car, etc.

Intangible Entity:

Intangible Entities are those entities which exist only logically and have no physical existence.

Example: Bank Account, etc...

 

Entity Type The entity type is a collection of the entity having similar attributes.

In the above Student table example, we have each row as an entity and they are having common attributes i.e each row has its own value for attributes Roll_no, Age, Student_name and Mobile_no.

So, we can define the above STUDENT table as an entity type because it is a collection of entities having the same attributes.

So, an entity type in an ER diagram is defined by a name(here, STUDENT) and a set of attributes(here, Roll_no, Student_name, Age, Mobile_no).

The table below shows how the data of different entities( different students) are stored...

 

1. https://www2.cs.sfu.ca/CourseCentral/354/zaiane/material/notes/Chapter2/node2.html