Question: Explain difference between strong entity set and weak entity set.
Strong Entity:
Weak Entity:
Strong Entity:
Strong entity is not dependent of any other entity in schema. Strong entity always has primary key. Strong entity is represented by single rectangle. Two strong entity’s relationship is represented by single diamond.
Various strong entities together makes the strong entity set.
Weak Entity:
Weak entity is depend on strong entity to ensure the existance of weak entity. Like strong entity weak entity does not have any primary key, It has partial discriminator key. Weak entity is represented by double rectangle.
The relation between one strong and one weak entity is represented by double diamond.
Difference between Strong entity set and Weak entity set:
| Basic | The Strong entity has a primary key. | The weak entity has a partial discriminator key. |
| Depends | The Strong entity is independent of any other entity in a schema. | Weak entity depends on the strong entity for its existence. |
| Denoted | Strong entity is denoted by a single rectangle. | Weak entity is denoted with the double rectangle. |
| Relation | The relation between two strong entities is denoted by a single diamond simply called relationship. | The relationship between a weak and a strong entity is denoted by Identifying Relationship denoted with double diamond. |
| Participation | Strong entity may or may not have total participation in the relationship. | Weak entity always has total participation in the identifying relationship shown by double line. |
