Entity in DBMS
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Database Management Systems (DBMS) are vital for effective data management, storing, and retrieval. Entities, fundamental to any DBMS, represent real-world objects or concepts within the database. This article delves into the significance of entities in DBMS, elucidating their crucial role in data representation and management. Understanding entities provides a foundational comprehension of the intricate structure and functionality of Database Management Systems.
Entity Set
An entity set in DBMS is a set that collectively represents a group of entities of a similar type.
For Example:
An entity set of cars, an entity set of bank accounts, etc. In DBMS, the whole table in the tabular representation of data is an entity set, while each row inside this table is an entity. Below is the tabular representation, i.e., entity set of bank accounts.
In entity-relationship diagrams, entity sets are represented by a rectangle, and the attributes of an entity set are represented by an ellipse.
Below is the representation of the bank entity accounts set in an entity-relationship diagram.
Weak Entity Set
Weak entity set in DBMS is an entity set that does not have a primary key, i.e., there exists no attribute that can uniquely represent each entity in the entity set.
For Example: An entity set of cars having attributes such as a car's color, a car's name is a weak entity since two cars can have the same color as well as the same name. So, none of the attributes can be considered as the primary key and hence the entity set is a weak entity set.
In entity-relationship diagrams, weak entity sets are represented by a double rectangle.
Strong Entity Set
**Strong entity set in DBMS is the entity set in which there exists a primary key, i.e., there exists an attribute that can uniquely represent each element in the entity.
** For Example:**, An entity set of cars having attributes such as a car's registration number, car's color, car's name is a strong entity since no two cars can have the same registration number. So, the attributes registration number can be considered as the primary key, and hence the entity set is a strong entity set.
In entity-relationship diagrams, strong entities are represented by a rectangle.
Difference between an Entity and an Entity Set
- An entity in DBMS is used to represent any real-world object, while an entity set in DBMS is a set or collection of entities of similar types.
- In relational models, i.e., the tabular representation to represent data, each row in a table is a separate entity while the whole table is an entity set.
- We cannot represent an entity in an entity-relationship diagram in DBMS (ER diagram) while entity sets are represented using a rectangle in an entity-relationship diagram (ER diagram).
- An entity contains the actual data, while an entity set contains the blueprint of an entity.
Conclusion
- In this article, all the important concepts required to understand the concept of entity in Database Management System are discussed along with the relevant examples.
- The difference between an entity and an entity set is discussed in this article.
- Different types of entity sets, such as weak entity sets and strong entity sets are also discussed in this article.