Hamish Burke | 2025-05-26

Related to: #databases

Armstrong Inference Rules

Related to Functional Dependency

• Reflexivity: If $Y$ in $X$, then $X\to Y$

• Augmentation: From $X\to Y$ infer $XZ\to YZ$

• Transitivity: From $X\to Y$ and $Y\to Z$ infer $X\to Z$

• NOT armstrong

  • Union: From $X\to Y$ and $X\to Z$ infer $X\to YZ$
  • Decomposition: From $X\to YZ$ infer $X\to Y$ and $X\to Z$
  • Pseudo-transitivity: From $X\to Y$ and $YZ\to W$, infer $XZ\to W$

AB -> C
A -> E

AB -> EB
AB -> C
AB -> CEB union

CE -> D 
AB -> CE transititisititity
AB -> D