DBMS Notes

Inference Rule (IR)

  • Using the inference rule, we can derive additional FD (functional dependency) from the initial attribute set.

Types Of Inference Rule

The FD (Functional dependency) has 6 types of inference rule. Any rule can be used in-between two attributes

1. Reflexive Rule (IR1)

  • In the reflexive rule, if B is a subset of A, then A determines B.
  • Every attribute can determine itself also called Reflexive.
  • If A ⊇ B then A  →   B


A ⊇  A , B  →  B  , AB  →    B

2. Augmentation Rule (IR2)

  • The augmentation rule is also called as a partial dependency.
  • If A    → B then AC   →   BC   

3. Transitive Rule (IR3)

  • In the transitive rule, if A determines B and B determine C, then A must also determine C.
  • If A   →   B and B  →  C, then A  →   C    

4. Union Rule (IR4)

  • Union rule says, if A determines B and B determines C, then A must also determine B and C.
  • If A  →  B and A   →  C then A  →    BC     

5. Decomposition Rule (IR5)

  • Decomposition rule is also called project rule. It is the reverse of union rule.
  • If A → BC then A → B and A →    C   

6. Pseudo transitive Rule (IR6)

  • According to Pseudo transitive Rule
  • If A   → B and BC   →   W then AC   →   W 
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