Definition
In database management systems, an entity set is a grouping of related entity types in a database. A set is an arrangement of all identical entities that are members of the same entity type.
In this case, each entity in a collection is referred to in the database as an instance. All employees, for instance, are listed in the employee database. Another illustration would be an entity set called Course, which has all of the course information and each course data point represents an instance of the Course entity set.
Types of Entity Set in DBMS
There are different types of Entity Set in DBM,S and they are classified based on entity characteristics and relationships between more than one entity. Entity sets in DBMS are :
1. Strong Entity Set
A strong entity set is one that has a primary key and lives independently in the database. As a stand-alone set, it is independent of all other entity sets.
Individual courses can be individually recognized using the course_id, course_code_id, or a combination of many entities, making the entity set named "Course" in a college database, for instance, a strong entity set.
2. Weak Entity Set
An entity set that depends on another entity and lacks a primary key but has a foreign key that aids in its unique identification (such as a parent entity) is said to be weak.
For example, the entity set "Student_Enroll" in a college database is weak because it cannot be uniquely identified without the course_id and student_id dependencies.
3. Associative Set
A relationship between multiple entity sets is represented by an associative entity set. This also has a primary key, but it is the main key of linked entities rather than an individual key.
An entity set named "Project_Work," for example, was made to specify the relationship between two other entity sets named "Student" and "Mentor." Using a combination of the main keys from the Student and Mentor entity sets, this entity set "Project_Work" can identify itself and include properties such as project_start and project_end dates.
4. Recursive Set
The relationship with itself is represented by this entity set in a recursive manner. This set is known as a self-referencing entity set because an instance of one entity set may be connected to another instance of the same entity set.
