Chapter 6: Query Decomposition and Data Localization
Chapter 6: Query Decomposition and Data Localization
Chapter 6: Query Decomposition and Data Localization
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<strong>Query</strong> <strong>Decomposition</strong> – Rewriting . . .<br />
• Commuting selection with binary operations<br />
– σ p(A) (R × S) ⇐⇒ σ p(A) (R) × S<br />
– σ p(A1 )(R ⋊⋉ p(A2 ,B 2 ) S) ⇐⇒ σ p(A1 )(R) ⋊⋉ p(A2 ,B 2 ) S<br />
– σ p(A) (R ∪ T) ⇐⇒ σ p(A) (R) ∪ σ p(A) (T)<br />
∗ (A belongs to R <strong>and</strong> T )<br />
• Commuting projection with binary operations (assume C = A ′ ∪ B ′ ,<br />
A ′ ⊆ A, B ′ ⊆ B)<br />
– Π C (R × S) ⇐⇒ Π A ′(R) × Π B ′(S)<br />
– Π C (R ⋊⋉ p(A ′ ,B ′ ) S) ⇐⇒ Π A ′(R) ⋊⋉ p(A ′ ,B ′ ) Π B ′(S)<br />
– Π C (R ∪ S) ⇐⇒ Π C (R) ∪ Π C (S)<br />
DDB 2008/09 J. Gamper Page 12
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