What is a weak entity in DBMS? Why is it called weak?

In the context of Database Management Systems (DBMS) and entity-relationship modeling, a weak entity is defined by several key characteristics that distinguish it from a strong entity.

Lack of Primary Key

A weak entity is an entity that cannot be uniquely identified by its own attributes alone. It does not have a primary key attribute that can distinguish each of its instances uniquely125.

Dependence on Strong Entity

A weak entity relies on another entity, known as the owner entity, parent entity, or strong entity, for its unique identification. The weak entity uses a combination of its own attributes (known as a partial key or discriminator) and the primary key of the strong entity to form a composite key. This composite key is necessary to uniquely identify each instance of the weak entity235.

Total Participation

Weak entities always have total participation in the relationship with their strong entities. This means that every instance of the weak entity must be associated with exactly one instance of the strong entity. This relationship is often represented by a double line in ER diagrams, indicating an identifying relationship125.

No Autonomous Existence

Weak entities cannot exist independently; their existence is subordinate to the existence of their associated strong entities. For example, in a university database, a "Section" entity might be a weak entity because it cannot exist without being associated with a "Course" entity23.

The term weak entity is used because these entities lack the autonomy and unique identification that strong entities possess. They are "weak" in the sense that they depend on another entity for their identity and cannot stand alone.