org.deri.iris.rules
Class RuleValidator

java.lang.Object
  org.deri.iris.rules.RuleValidator

public class RuleValidator
extends Object

We use the definition of a safe rule as described by Ullman, page 105. A rule is safe if all variables are limited. A variable is limited if: 1) It appears in a positive ordinary predicate 2) It appears in a positive equality with a constant, e.g. ?X = 'a' 3) It appears in a positive equality with another variable known to be limited, e.g. ?X = ?Y, ?Y = 'a' However, variables that ONLY appear in a negated ordinary predicate (and nowhere else) can still make for a safe rule, as such a rule can be re-written to move the negated sub-goal to a separate rule, see the example in Ullman, page 129-130 Furthermore, variables that appear in arithmetic predicates can also be considered limited if all the remaining variables are limited, e.g. X + Y = Z, X = 3, Z = 4, implies that Y is also limited These two relaxations of the definition of a safe rule are configurable (on/off).

Constructor Summary

RuleValidator(IRule rule, boolean allowNotLimitedVariablesInNegatedSubGoals, boolean allowArithmeticPredicatesToImplyLimited)
Constructor.

Method Summary

List<IVariable>

getAllUnlimitedVariables()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RuleValidator

public RuleValidator(IRule rule,
                     boolean allowNotLimitedVariablesInNegatedSubGoals,
                     boolean allowArithmeticPredicatesToImplyLimited)

Constructor. Each instance of this rule can process exactly one rule, after which it must be discarded.

Parameters:

allowNotLimitedVariablesInNegatedSubGoals - false, if the strict Ullman definition should be enforced for variables in negated sub-goals.

limitedTernaryOperandsImplyLimitedResult - false, if the strict Ullman definition should be enforced for variables in that are in arithmetic predicates.

Method Detail

getAllUnlimitedVariables

public List<IVariable> getAllUnlimitedVariables()