Database-Management-System
August 26, 2024Database-Management-System
August 26, 2024Database-Management-System
| Question 635 |
Which of the following statements is FALSE about weak entity set?
| Weak entities can be deleted automatically when their strong entity is deleted. | |
| Weak entity set avoids the data duplication and consequent possible inconsistencies caused by duplicating the key of the strong entity. | |
| A weak entity set has no primary keys unless attributes of the strong entity set on which it depends are included | |
| Tuples in a weak entity set are not partitioned according to their relationship with tuples in a strong entity set. |
Question 635 Explanation:
A weak entity always have total participation relationship with strong entity. It means that every entry in weak entity set will participate in relationship with strong entity and if a strong entity on which weak entity depends is deleted then total participation condition is exploited. So to avoid this Weak entities are deleted automatically when their strong entity is deleted. So option (A) is correct.
Option (B) is correct. A weak entity is an entity which do not have any primary key to uniquely identify its each entry and this leads to data duplication and data inconsistency in the weak entity. So to avoid this problem the key of a strong entity is duplicated into weak entity to uniquely identify each entry of a weak entity. So option (B) is correct.
Option (C) is also correct. Because until the key attributes of a owner strong entity of a weak entity are not included each entry of weak entity can’t be uniquely identified.
Option (D) is false because tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set.
In above example the key attribute of “Employee” (which is a strong entity) is partitioning the the tuples of “Dependent” (which is a weak entity) based on the tuples belongs to Emp No. “1” and tuples belongs to Emp No. “2”.
So option(D) is false
Option (B) is correct. A weak entity is an entity which do not have any primary key to uniquely identify its each entry and this leads to data duplication and data inconsistency in the weak entity. So to avoid this problem the key of a strong entity is duplicated into weak entity to uniquely identify each entry of a weak entity. So option (B) is correct.
Option (C) is also correct. Because until the key attributes of a owner strong entity of a weak entity are not included each entry of weak entity can’t be uniquely identified.
Option (D) is false because tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set.
In above example the key attribute of “Employee” (which is a strong entity) is partitioning the the tuples of “Dependent” (which is a weak entity) based on the tuples belongs to Emp No. “1” and tuples belongs to Emp No. “2”.
So option(D) is false
Correct Answer: D
Question 635 Explanation:
A weak entity always have total participation relationship with strong entity. It means that every entry in weak entity set will participate in relationship with strong entity and if a strong entity on which weak entity depends is deleted then total participation condition is exploited. So to avoid this Weak entities are deleted automatically when their strong entity is deleted. So option (A) is correct.
Option (B) is correct. A weak entity is an entity which do not have any primary key to uniquely identify its each entry and this leads to data duplication and data inconsistency in the weak entity. So to avoid this problem the key of a strong entity is duplicated into weak entity to uniquely identify each entry of a weak entity. So option (B) is correct.
Option (C) is also correct. Because until the key attributes of a owner strong entity of a weak entity are not included each entry of weak entity can’t be uniquely identified.
Option (D) is false because tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set.
In above example the key attribute of “Employee” (which is a strong entity) is partitioning the the tuples of “Dependent” (which is a weak entity) based on the tuples belongs to Emp No. “1” and tuples belongs to Emp No. “2”.
So option(D) is false
Option (B) is correct. A weak entity is an entity which do not have any primary key to uniquely identify its each entry and this leads to data duplication and data inconsistency in the weak entity. So to avoid this problem the key of a strong entity is duplicated into weak entity to uniquely identify each entry of a weak entity. So option (B) is correct.
Option (C) is also correct. Because until the key attributes of a owner strong entity of a weak entity are not included each entry of weak entity can’t be uniquely identified.
Option (D) is false because tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set.
In above example the key attribute of “Employee” (which is a strong entity) is partitioning the the tuples of “Dependent” (which is a weak entity) based on the tuples belongs to Emp No. “1” and tuples belongs to Emp No. “2”.
So option(D) is false
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