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StudentClass Table

This article explains the BCNF Decomposition Algorithm, covering closure of attributes, missing information, and inference rules for functional dependencies and multivalued dependencies.

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StudentClass Table

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  1. StudentClass Table

  2. Missing Info?

  3. Closure of Attributes X Start with X+ = X Repeat until no change in X+ If there is Y -> Z with Y  X+, then Add Z to X+

  4. BCNF Decomposition Algorithm For any R in the schema If (X -> Y holds on R AND X -> Y is non-trivial AND X does not contain a key), then 1) Compute X+ (X+: closure of X) 2) Decompose R into R1(X+) and R2(X, Z) // X becomes common attributes // Z: all attributes in R except X+ Repeat until no more decomposition

  5. Class(cnum, ta, sid) Class 143 TA: Tony, James Students: 100, 101, 103 Class 248 TA: Tony, Susan Students: 100, 102

  6. Inference rules for FDs and MVDs • Reflexivity: If Y  X, then X -> Y • Augmentation: If X -> Y, then ZX -> ZY • Transitivity: If X -> Y and Y -> X, then X -> Z • Complementation: If X ->> Y, then X ->> R – (YX) • MVD augmentation: If X ->> Y and W  Z, then ZX ->> WY • MVD transitivity: If X ->> Y and Y ->> Z, then X ->> Z – Y • Replication: If X -> Y, then X ->> Y • Coalescence: If X ->> Y, W -> Y (Z  Y, WY=), then X -> Z The set of above rules are sound and complete

  7. 4NF Decomposition Algorithm For any R in the schema If (non-trivial X ->> Y holds on R AND X does not contain a key), then Decompose R into R1(X,Y) and R2(X,Z) // X becomes common attributes // Z: all attributes in R except (X, Y) Repeat until no more decomposition

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