DATABASE MANAGEMENT SYSTEM

WEAK ENTITY AND STRONG ENTITY

Strong Entity Set:

A strong entity set is an entity set that has a primary key attribute, which uniquely identifies each entity within the set.

The primary key is a minimal set of attributes that can uniquely identify an entity.

Strong entity sets do not depend on the existence of another entity set for their identification.

Example: In a university database, the "Student" entity set may be considered a strong entity set because each student can be uniquely identified by a student ID.

Weak Entity Set:

A weak entity set is an entity set that does not have a primary key attribute on its own.

The existence of entities in a weak entity set is dependent on the existence of another entity set, known as the owner or parent entity set.

Weak entities are typically identified by a partial key, which is a set of attributes that only uniquely identifies entities when used in conjunction with the owner entity's primary key.

Example: Consider a "Dependent" entity set that depends on a "Employee" entity set. The "Dependent" entity set might have attributes like pname, but to uniquely identify a Dependents, you need both the pname  and the Employee.