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Entity types that do not have key attributes of their own are called weak entity.
Entities belonging to weak entity type are identified by being related to specific strong entities.
These strong entities are called identifying entities and relationship with weak entity is called weak relationship.
Weak Entity is represented as:
Weak relationship is represented as:
A weak entity has a partial key which is the attribute that can uniquely identify weak entities that are related to another strong entity.
For example consider dependent entity, it is a weak entity as it do not have sufficient attributes to from a primary key.
It is connected with a strong entity employee.
Here the Name attribute is a partial key.
Using attributes Name, Age and relation it is not possible to uniquely identify depandant.
Thus dependent is weak entity and emp is corresponding identifying strong entity.