Strong Entity vs. Weak Entity — What's the Difference?

Another distinguishing factor is the representation in an Entity-Relationship (ER) diagram. Strong Entities are represented using rectangles, while Weak Entities are depicted using double rectangles. Additionally, the relationship between a Strong Entity and a Weak Entity is illustrated with a double diamond, denoting the dependency of the Weak Entity.

Conversely, a Weak Entity is one that cannot stand on its own. This means a Weak Entity's existence is reliant on another entity, typically a Strong Entity. Unlike Strong Entities, Weak Entities don't have a primary key that is unique to every instance. Instead, they possess a partial key. To uniquely identify a Weak Entity, you'd often require a combination of its partial key and the primary key of the Strong Entity it depends on.

The relationship dynamics between Strong and Weak Entities are crucial for relational database designs. For a Strong Entity, its relationships with other entities are based on its unique primary key. However, for a Weak Entity, relationships are more complex as they hinge on both the partial key of the Weak Entity and the primary key of its associated Strong Entity.

In the realm of database management and design, the term Strong Entity refers to an entity that can exist on its own without being dependent on any other entity. In essence, a Strong Entity is self-sufficient. Every instance of a Strong Entity has a unique identifier or primary key which distinguishes it from other entities. This primary key ensures that no two instances of a Strong Entity are identical, maintaining data integrity.