Definitions

• Integrity constraint (IC): a rule with an empty head that describes some semantic property of data.
  
  Example:
  :- m(X,Y), m(X,Z), Y!=Z



• Semantic query optimization (SQO): the process of using integrity constraints in order to optimize the evaluation of a query.
  
  Three types of SQO:
  1. Join elimination
  2. Restriction introduction
  3. Restriction elimination