Which of the following statements is false about weak entity set ?
2015
Which of the following statements is false about weak entity set ?
- A.
Weak entities can be deleted automatically when their strong entity is deleted
- B.
Weak entity set avoids the data duplication and consequent possible inconsistencies caused by duplicating the key of the string entity
- C.
A weak entity set has no primary keys unless attributes of the strong entity set on which it depends are included
- D.
Tuples in a weak entity set are not partitioned according to their relationship with tuples with a strong entity set
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Correct answer: D
Answer: The false statement is Tuples in a weak entity set are not partitioned according to their relationship with tuples with a strong entity set.
Reason:
Definition: A weak entity does not have a complete primary key of its own and depends on a strong (owner) entity through an identifying relationship.
Identifier formation: A weak entity has a partial key that must be combined with the owner's primary key attributes to form a unique identifier for each weak entity instance.
Partitioning: Because each weak entity instance is associated with a particular owner, weak entity tuples are naturally grouped or partitioned by their owner; uniqueness of the weak entity is scoped to each owner.
Behavior on deletion: The identifying relationship typically implies total participation of the weak entity, so deleting the owner usually leads to deletion of the dependent weak entities (a delete cascade in implementation).
Example: Consider apartment units identified by (building_id, unit_number). unit_number alone is not unique across buildings, so weak entity tuples (units) are partitioned by building (the owner).
Therefore, the claim that weak entity tuples are not partitioned by their relationship to a strong entity is incorrect.