An entity in DBMS represents a real-world object or concept that can be uniquely identified and stored in a database. It forms the foundation of data modeling in an Entity-Relationship (ER) model.
Example: A student, An employee, or bank a/c, etc. all are entities.
Entity Set
An entity set is a collection of similar types of entities that share the same attributes in a database. Each entity in the set represents a real-world object or concept. It can be classified into two types:
1. Strong Entity Set
A strong entity set is an independent entity with a unique primary key that distinguishes each of its instances.
Example of Strong Entity includes:
- Car Registration Number
- Model
- Name etc.
2. Weak Entity Set
A weak entity set depends on a strong entity for identification. It lacks a unique primary key and uses a partial key combined with the strong entity's key.
Example of Weak Entity Set includes:
- Laptop Color
- RAM, etc.
Kinds of Entities
There are two types of Entities:
1. Tangible Entity
A tangible entity is a physical object or a physical thing that can be physically touched, seen or measured. It has a physical existence or can be seen directly.
Now lets understand this with the help of example:
Examples of Tangible entities are real, physical things like products (e.g., inventory items) or people (e.g., customers and employees).
2. Intangible Entity
Intangible entities are abstract or conceptual objects that are not physically present but have meaning in the database. They are typically defined by attributes or properties that are not directly visible.
Now lets understand this with the help of example:
Examples of Intangible entities are non-physical things like concepts (e.g., product categories, service types) or events (e.g., appointments, transactions).
Entity Types in DBMS
There are two types of Entity:
- Strong Entity Types: These are entities that exist independently and have a completely unique identifier.
- Weak Entity Types: These entities depend on another entity for his or her lifestyles and do now not have a completely unique identifier on their own.
Example of Strong and Weak Entity Types in DMBS is:
- Associative Entity Types: These represent relationships between two or more entities and may have their own attributes.
- Derived Entity Types: These entities are derived from different entities through a system or calculation.
- Multi-Valued Entity Types: These entities will have more than one value for an characteristic.
Difference Between Entity and Entity Set
Here is a comparison of Entity and Entity Set based on various features:
| Entity | Entity Set |
|---|---|
| A single real-world object or instance. | A collection of similar entities. |
| Represents one specific car. | Represents all cars in the system. |
| One row in a table. | All rows in the "Car" table. |
| Specific values like Registration_No: KA01AB1234, Name: Toyota. | Common attributes like Name, Model, Color, No_of_Seats. |
| A single car. | A "Car" set containing all car records. |
| Identified by a unique Registration_No. | Identified by the primary key across all cars. |
| Stores one car's data. | Manages data for all cars. |
| Represents one physical car. | Organizes and manages all cars as a group. |
Let's understand this difference with help of Diagram:
