Database-Management-System
August 29, 2024Functional-Dependency
August 29, 2024Database-Management-System
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Question 672
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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________.
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Dependency preserving but not lossless join
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Dependency preserving and lossless join
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Lossless join but not dependency preserving
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Neither dependency preserving nor lossless join.
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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.