Strong Entity vs. Weak Entity

Main Difference

The main difference between a strong entity and the weak entity is that a strong entity is the one that does not need any other entity to depend on, whereas a weak entity is an entity that needs a strong entity to depend on.

Difference Between Strong Entity and Weak Entity

Comparison Chart

Strong Entity vs. Weak Entity

The strong entity is the one that does not need any other entity for its dependence. A weak entity is an entity that needs a strong entity to depend on. The strong entity uniquely identifies its attributes because it is independent; on the other hand, a weak entity does not uniquely identify its attributes because it is dependent. The strong entity contains a primary key, while the weak entity contains a partial key discriminator. The strong entity is independent, whereas the weak entity depends on the strong entity. In a strong entity, the primary key is represented by underline, whereas in the weak entity, partial key or a discriminator is represented by a dashed underline. The strong entity members are called as the dominant entity set, while the weak entity members are called subordinate entity set.

The identification of a strong entity is a single rectangle conversely; the identification of a weak entity is the double rectangle. In a strong entity, a diamond symbol represents the relationship between two strong entity set, whereas the double diamond symbol represents the identifying relationship between one strong entity and a weak entity set. The connection between a strong entity set to the relationship is by a single line, while the double lines connect a weak entity set to the relationship. The participation level of a strong entity in a relationship may or may not exist, whereas the participation level of the weak entity in the identifying relationship always exists.

What is strong entity?

The strong entity is independent that is why it does not need support from any other entities. The identification of a strong entity is represented through a single rectangle. The strong entity owns a key attribute that uniquely identifies its attributes because it is independent and has a primary key. In a strong entity, the primary key is defined by an underline. The strong entity is independent, whereas the weak entity depends on the strong entity. The strong entity members are called as the dominant entity set.

The set or a group of same strong entities combine to form a strong entity set. In a strong entity, a diamond symbol represents the relationship between two strong entity set, whereas the double diamond symbol represents the identifying relationship between one strong entity and a weak entity set. The bond of a strong entity set to the relationship is shown through a single line. The participation level of a strong entity in a relationship may or may not exists.

What is weak entity?

A weak entity is an entity that always requires a strong entity to depend on; that is why the strong entity is the owner of the weak entity. A weak entity does not uniquely identify its attributes because it is dependent on the strong entity. The weak entity always requires a strong entity to identify its worth. The weak entity does not own the primary key. Instead of a primary key, the weak entity has a partial key discriminator that uniquely identifies the weak entities. In the ER diagram, the weak entity consists of a partial key or a discriminator, which is represented through a dashed underline.

The identification of a weak entity is the double rectangle. The set or a group of same weak entities combine to form a weak entity set. The weak entity members are called subordinate entity set. The bond between weak and strong entity set is known as the “identifying relationship.” The representation of double diamonds indicates the relationship between one strong entity and a weak entity set. The participation level of the weak entity in the identifying relationship always exists. The bond of a weak entity set to the relationship is shown through double lines.

Conclusion

An entity represents the data, which is a real-world object. The entities have two types that are strong and weak entity: the strong entity is independent and does not require any other entity to identify it, whereas the weak entity depends on the strong entity.