Database-Management-System
August 29, 2024Functional-Dependency
August 29, 2024Database-Management-System
| Question 672 |
Consider a schema R(MNPQ) and functional dependencies M → N, P → Q. Then the decomposition of R into R 1 (MN) and R 2 (PQ) is________.
| Dependency preserving but not lossless join | |
| Dependency preserving and lossless join | |
| Lossless join but not dependency preserving | |
| Neither dependency preserving nor lossless join. |
Question 672 Explanation:
Definition of lossless decomposition: Let R be the relational schema decomposed into R 1
and R 2 . Given decomposition is lossless only if
1. R 1 U R 2 =R
2. R 1 U R 2 =φ
3. R 1 ∩ R 2 → R 1 (or) R 1 ∩ R 2 → R 2
→ In this schema, there is no common key attribute between R 1 and R 2 . So, this relation is lossy relation.
Definition of Functional dependency preserving:
→ Let R be the relational schema with functional dependency set F is decomposed into R 1 , R 2 ,..,R n with functional dependency sets F 1 ,F 2 ,…,F n respectively. In general F 1 ,F 2 ,…,F n can be ⊆ F.
So, dependencies are preserved in the given decomposition.
and R 2 . Given decomposition is lossless only if
1. R 1 U R 2 =R
2. R 1 U R 2 =φ
3. R 1 ∩ R 2 → R 1 (or) R 1 ∩ R 2 → R 2
→ In this schema, there is no common key attribute between R 1 and R 2 . So, this relation is lossy relation.
Definition of Functional dependency preserving:
→ Let R be the relational schema with functional dependency set F is decomposed into R 1 , R 2 ,..,R n with functional dependency sets F 1 ,F 2 ,…,F n respectively. In general F 1 ,F 2 ,…,F n can be ⊆ F.
So, dependencies are preserved in the given decomposition.
Correct Answer: A
Question 672 Explanation:
Definition of lossless decomposition: Let R be the relational schema decomposed into R 1
and R 2 . Given decomposition is lossless only if
1. R 1 U R 2 =R
2. R 1 U R 2 =φ
3. R 1 ∩ R 2 → R 1 (or) R 1 ∩ R 2 → R 2
→ In this schema, there is no common key attribute between R 1 and R 2 . So, this relation is lossy relation.
Definition of Functional dependency preserving:
→ Let R be the relational schema with functional dependency set F is decomposed into R 1 , R 2 ,..,R n with functional dependency sets F 1 ,F 2 ,…,F n respectively. In general F 1 ,F 2 ,…,F n can be ⊆ F.
So, dependencies are preserved in the given decomposition.
and R 2 . Given decomposition is lossless only if
1. R 1 U R 2 =R
2. R 1 U R 2 =φ
3. R 1 ∩ R 2 → R 1 (or) R 1 ∩ R 2 → R 2
→ In this schema, there is no common key attribute between R 1 and R 2 . So, this relation is lossy relation.
Definition of Functional dependency preserving:
→ Let R be the relational schema with functional dependency set F is decomposed into R 1 , R 2 ,..,R n with functional dependency sets F 1 ,F 2 ,…,F n respectively. In general F 1 ,F 2 ,…,F n can be ⊆ F.
So, dependencies are preserved in the given decomposition.
Subscribe
Login
0 Comments