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Why is weak entity important?
i.e., it cannot exist without the entity with which it has a relationship. It inherits at least part of it’s primary key from the entity to which it is related. i.e. -> A weak entity’s primary key must be a composite key that includes the primary key of the entity on which it is existence-dependent.
When should an entity be weak?
An entity is weak when two conditions are met: The entity is existence-dependent on another entity. The entity gets at least part of its primary key from that other entity.
What is the necessity of keeping weak entity sets in an ER model representation?
Weak entity is depend on strong entity to ensure the existence 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.
How can you convert a weak entity to a strong entity?
We can convert any weak entity set to a strong entity set by simply adding appropriate attributes.
Can a weak entity have a relationship with another weak entity?
‘Can a weak entity be related to another weak entity’ I would say No. A weak entity has no primary key of its own but does have a foreign key which is linked to the PK of another entity. Thus if you have two weak entities with the same FK id they are infact related to the same strong entity rather than each other.
What do you call a weak entity set?
An entity type should have a key attribute which uniquely identifies each entity in the entity set, but there exists some entity type for which key attribute can’t be defined. These are called Weak Entity type.
Why do we need weak entity in database design?
In physical design we may choose to implement “weak” tables to reduce the number of joins in some queries. Continuing the example, if we make Customer Number part of the key to Order and also to Order Line then a query to count how many widgets the Jones Trading Company has ordered need only touch one table.
How is a weak entity represented in ER?
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.
How are partial keys used to identify weak entities?
Partial Keys are set of attributes with the help of which the tuples of the weak entities can be distinguished and identified. Note – Weak entity always has total participation but Strong entity may not have total participation.