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To understand Database management systems foundationally, you should know what is an entity in DBMS. Entity is a fundamental and key concept to understanding database design. An entity in DBMS is any object that can be distinguished from other objects in the real world. It is a unique object that can be identified within database systems. In this blog, we will understand the meaning of an entity in DBMS, its different types, examples, and much more.
An entity is a significant “thing” or “object”, idea, or tangible or intangible element, that can be identified uniquely and stored in a database. Entities in databases are easily identified like a student, employee, car, bank, bike, etc. Entities play the role of data storage and are used for organising and managing the data in a database. Attributes or characteristics are the one that describes and defines an entity uniquely.
For example, A car is an entity that has attributes like a model, colour, year, etc., and A bank is an entity that has attributes like branch name, IFSC code, etc. A Student is an entity that has attributes like a name, roll no, major, etc., An employee is an entity that has attributes like an emp_name, emp_id, emp_dept, etc. So, these are some common and real-life entities examples through which you can easily understand the concept of entities in DBMS.
Relationships are an important part of the entities as significant for the structuring and the easy retrieval of data. Relationships are often related to each other and use different kinds of keys to create a relation between them In DBMS, typically there are 3 types of relationships. They include:
Attributes are the important characteristics of entities that help those instances provide the important details of themselves. There are various types of attributes of an entity that include:
Till now, we have understood the basics of Entities in DBMS including the types of relationships and attributes. Let’s now understand the types of Entities in DBMS.
Entities in DBMS are of different types which are distinguished based on their characteristics and the context in which they are used. We will see the common and most used types of entities in DBMS. The types of entities in DBMS include:
A Strong Entity is a type of entity in DBMS that has a key attribute and a unique identifier. A strong entity is also known as an independent entity in DBMS. This entity is capable of existing in a database relation without any other entity. A strong entity is also a primary key or a key attribute that helps this entity to identify each instance of the entity uniquely. These entities exist in real words and are represented as objects.
Let’s see some real-world examples to understand the strong entity:
Examples:
A weak entity is a type of entity in DBMS that cannot exist in the database without a strong entity. As a strong entity consists of a primary key (a unique identifier), the weak entity has no primary key. A weak entity is also known as a dependent entity in DBMS. To ensure its uniqueness, it takes the help of the strong entity and relies on a concept called foreign key relationship. This entity also represents a part or a component of the strong entity in the database.
Let’s see some real-world examples to understand the weak entity:
Examples:
A composite entity in DBMS is a type of associative entity or junction table that represents the many-to-many relationships between the two different strong entities in a database. As the name’s meaning implies, it is composed of two or more strong entities that include the foreign keys from different related entities of the database.
Let’s see some real-world examples to understand the composite entity:
Examples:
Entity types are classified further as two different types according to their nature and physical existence. It includes:
1. Tangible Entity
A tangible entity is an entity that exists in the physical world and can be touched. Examples of tangible entities include cars, bikes, employees, etc., as they exist physically and can be touched too.
2. Intangible Entity
An intangible entity is an entity that does not exist in the physical world and can’t be touched. It is the opposite of tangible entities. Examples of intangible entities include bank transactions, orders, etc., as they do not exist physically and can’t be touched too but are essential for various purposes.
Entity type is a combination of related entities that have common characteristics and features. They are used commonly in entity-relationship (ER) diagrams with the symbol of the rectangle. For example, in a movie database, there may be entity types including movie_genre, movie_platform_released, etc. These similar entity types share common attributes and characteristics. Entity types are of different types and include:
An entity set in DBMS is a collection of similar types of entities in a database. Set means a group of all the same entities that belong to the same entity type. Here, each entity within a set is called an instance in the database.
For example, all employees belong to the employee database. Another example could be an entity set Course that consists of all the course details where each course data represents the instance of the Course entity set.
There are different types of entity sets in DBMS and they are classified based on the entity’s characteristics and relationships between more than one entity. Entity sets in DBMS include:
For example, in a college database, the entity set called “Course” is a strong entity set as individual courses can be identified uniquely using the course_id, or course_code_id, or with a combination of different entities.
For example, in a college database, the entity set called “Student_Enroll” is a weak entity set as it can’t be identified uniquely without the dependence of the course_id and student_id.
For example, an entity set called “Project_Work” was created to define the relation between two other entity sets called “Student” and “Mentor”. This entity set “Project_Work” may consist of attributes like project_start and project_end dates and identify itself using a combination of primary keys of both Student and Mentor entity sets.
Parameters | Entity | Entity Set |
Define | An entity is an object or an idea in a database. | An entity set is a collection of the same kind of entities. |
Existence | An entity represents one instance in a database. | An entity set represents the multiple or a group of instances in a database. |
Row representation | It is any specific record within a table of a database. | They are all records within a table of a database. |
Attributes | Attributes of an entity may include name, address, phone, etc. | Attributes of an entity set called a Product may include attributes like P_name, P_id, etc. |
Example | A customer is an entity. | A “customer” set which consists of all consumer details. |
Identification | An entity can be identified using its primary key which is available in the relation. | An entity set can be identified using its primary key which is available in the entity set of a relation. |
Usage | An entity is mostly used to store a single instance of information in the relation. | An entity set is mostly used to store and manage a collection of instances of information in the relation. |
Purpose | To represent the single instance of a real-world object. | To represent, organise, and manage the collection of instances of an entity set in a relation. |
In this blog, we delved deep into what is an entity in DBMS. Entities in DBMS represent the real-world object that consists of different attributes to identify them with others. We learned what is an entity, what are its types, its attributes, and many other elements. Having an understanding of the different types of entities, database engineers can create well-structured and optimised databases. Applying the discussed relationships and considering the types of entities while creating a database, can lead to data integrity, efficient data retrieval, etc.
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