BSc IT - Database Management System

In a DBMS , a strong entity  is an entity that can be uniquely identified by its own attributes without depending on any other entity. It has a primary key  and can exist independently in the database. For example, a Student entity with a unique StudentID is a strong entity because it doesn’t rely on any other table to exist. 

On the other hand, a weak entity  cannot be uniquely identified by its own attributes alone. It depends on another entity, called the strong entity , for its identity. A weak entity does not have a primary key of its own but uses a combination of its partial key  and the primary key of the strong entity to form a composite key . For example, an OrderItem entity may depend on an Order entity — without an order, an order item cannot exist.