Weak Entity Set¶
A weak entity set is one that has to rely on another entity set for its existence
- This entity is known as its identifying entity
- Instead of associating a primary key with a weak entity, we use the identifying entity, (along with extra attributes called the discriminator) to uniquely identify a weak entity
- The identifying entity set is said to own the weak entity set
- This relationship is referred to as an identifying relationship
Representation of Weak Entity Set¶
- A weak entity is represented in an E-R diagram with a double rectangle
- The discriminator is underlined with a dashed line
- The relationship set connecting the weak entity to the identifying relationship is depicted as a double diamond