Difference between Strong Entity and Weak Entity

Basically, Entity is a thing, or an object and it has different properties when compared to the other objects. The entities are widely used in the database management systems. There are mainly two different types of entities are present in the database management system. Both strong and weak entities have their own properties based on the uniqueness of the object. The object is categorized into weak entity or the strong entity. So, we are going to know the differences between the two types of entities and also about where these entities are used in Database management.

What is Strong Entity?

Strong Entity can be defined as an entity which does not depend on the other entities present in the database. The properties of the strong entity will also be different from the other entities in the database. The Strong entities are always independent. A strong entity can also be named as the Owner entity. Strong entity always uses the primary key field in a particular table that is present in the database. The Strong entity is always represented using a rectangular box in the E-R diagrams of the databases. All the strong entities collectively called as the strong entity set, the strong entity sets are also represented using the same rectangular boxes in the E-R diagrams of the databases. A relationship called Identifying relationship is used to establish the relationship between a strong entity and a weak entity set in a table. The Strong entity in a table is identified based on the primary key attribute present in the table. The identified primary key attribute will be used or represented as the strong entity in the particular table. The Strong entities do not show total participation in the relationship with the other weak entities present in the table.

What is Weak Entity?

Weak Entity can be defined as an entity which depends on the other entities present in the table. The weak entities are always dependent. The Weak entity can also depend on the Strong entity or the Owner entity that are present in the table. Weak does not use any key constrains like primary key, candidate key and the other key constrains present in the table. But the Weak entity uses partial key, but the partial key is not included in the key constrains. Weak entity is always represented using a double rectangular symbol and this symbol is used in the E-R diagrams of the database. All the Weak entities present in the table collectively called as the Weak entity set. The weak entities with similar properties are only included in the Weak entity sets. The Identifying relationship is also used by the Weak entity to maintain the relation between the Strong entity and the Weak entity. The Weak entities are not unique and have some similarities with the attributes of the Strong entity.

Advantages of Strong Entity

The Strong entity is used to find the primary key attributes which will be unique.
The Strong entity helps in identifying the useful information from the table.

Advantages of Weak Entity

With the help of weak entity we can find out the columns that are depending over the other columns.
The Weak entity always shows the total participation in the relationship.

Disadvantages of Strong Entity

The Strong entities do not show total participation in the relationship with the other weak entities present in the table.
We can only find the primary keys and the other key constrains are identified.

Disadvantages of Weak Entity

The weak entity attributes are always connected to the attributes of the Strong entity.
It always depends on the other attributes if the other attributes are disturbed then it is also disturbed.