Example 1 with DisjunctiveHead
use of at.ac.tuwien.kr.alpha.api.rules.heads.DisjunctiveHead in project Alpha by alpha-asp.
the class VariableEqualityRemoval method findAndReplaceVariableEquality.
private Rule<Head> findAndReplaceVariableEquality(Rule<Head> rule) {
// Collect all equal variables.
HashMap<VariableTerm, HashSet<VariableTerm>> variableToEqualVariables = new LinkedHashMap<>();
HashSet<Literal> equalitiesToRemove = new HashSet<>();
for (Literal bodyElement : rule.getBody()) {
if (!(bodyElement instanceof ComparisonLiteral)) {
continue;
}
ComparisonLiteral comparisonLiteral = (ComparisonLiteral) bodyElement;
if (!comparisonLiteral.isNormalizedEquality()) {
continue;
}
if (comparisonLiteral.getTerms().get(0) instanceof VariableTerm && comparisonLiteral.getTerms().get(1) instanceof VariableTerm) {
VariableTerm leftVariable = (VariableTerm) comparisonLiteral.getTerms().get(0);
VariableTerm rightVariable = (VariableTerm) comparisonLiteral.getTerms().get(1);
HashSet<VariableTerm> leftEqualVariables = variableToEqualVariables.get(leftVariable);
HashSet<VariableTerm> rightEqualVariables = variableToEqualVariables.get(rightVariable);
if (leftEqualVariables == null && rightEqualVariables == null) {
HashSet<VariableTerm> equalVariables = new LinkedHashSet<>(Arrays.asList(leftVariable, rightVariable));
variableToEqualVariables.put(leftVariable, equalVariables);
variableToEqualVariables.put(rightVariable, equalVariables);
}
if (leftEqualVariables == null && rightEqualVariables != null) {
rightEqualVariables.add(leftVariable);
variableToEqualVariables.put(leftVariable, rightEqualVariables);
}
if (leftEqualVariables != null && rightEqualVariables == null) {
leftEqualVariables.add(rightVariable);
variableToEqualVariables.put(rightVariable, leftEqualVariables);
}
if (leftEqualVariables != null && rightEqualVariables != null) {
leftEqualVariables.addAll(rightEqualVariables);
for (VariableTerm rightEqualVariable : rightEqualVariables) {
variableToEqualVariables.put(rightEqualVariable, leftEqualVariables);
}
}
equalitiesToRemove.add(comparisonLiteral);
}
}
if (variableToEqualVariables.isEmpty()) {
// Skip rule if there is no equality between variables.
return rule;
}
List<Literal> rewrittenBody = new ArrayList<>(rule.getBody());
if (!rule.isConstraint() && rule.getHead() instanceof DisjunctiveHead) {
throw new UnsupportedOperationException("VariableEqualityRemoval cannot be applied to rule with DisjunctiveHead, yet.");
}
NormalHead rewrittenHead = rule.isConstraint() ? null : Heads.newNormalHead(((NormalHead) rule.getHead()).getAtom());
// Use substitution for actual replacement.
Unifier replacementSubstitution = new Unifier();
// For each set of equal variables, take the first variable and replace all others by it.
for (Map.Entry<VariableTerm, HashSet<VariableTerm>> variableEqualityEntry : variableToEqualVariables.entrySet()) {
VariableTerm variableToReplace = variableEqualityEntry.getKey();
VariableTerm replacementVariable = variableEqualityEntry.getValue().iterator().next();
if (variableToReplace == replacementVariable) {
continue;
}
replacementSubstitution.put(variableToReplace, replacementVariable);
}
// Replace/Substitute in each literal every term where one of the common variables occurs.
Iterator<Literal> bodyIterator = rewrittenBody.iterator();
while (bodyIterator.hasNext()) {
Literal literal = bodyIterator.next();
if (equalitiesToRemove.contains(literal)) {
bodyIterator.remove();
}
for (int i = 0; i < literal.getTerms().size(); i++) {
Term replaced = literal.getTerms().get(i).substitute(replacementSubstitution);
literal.getTerms().set(i, replaced);
}
}
// Replace variables in head.
if (rewrittenHead != null) {
Atom headAtom = rewrittenHead.getAtom();
for (int i = 0; i < headAtom.getTerms().size(); i++) {
Term replaced = headAtom.getTerms().get(i).substitute(replacementSubstitution);
headAtom.getTerms().set(i, replaced);
}
}
return new BasicRule(rewrittenHead, rewrittenBody);
}
Also used :
LinkedHashSet(java.util.LinkedHashSet)
BasicRule(at.ac.tuwien.kr.alpha.core.rules.BasicRule)
ArrayList(java.util.ArrayList)
DisjunctiveHead(at.ac.tuwien.kr.alpha.api.rules.heads.DisjunctiveHead)
Term(at.ac.tuwien.kr.alpha.api.terms.Term)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
Atom(at.ac.tuwien.kr.alpha.api.programs.atoms.Atom)
LinkedHashMap(java.util.LinkedHashMap)
NormalHead(at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)
Literal(at.ac.tuwien.kr.alpha.api.programs.literals.Literal)
ComparisonLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)
VariableTerm(at.ac.tuwien.kr.alpha.api.terms.VariableTerm)
ComparisonLiteral(at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)
HashMap(java.util.HashMap)
LinkedHashMap(java.util.LinkedHashMap)
Map(java.util.Map)
Unifier(at.ac.tuwien.kr.alpha.commons.substitutions.Unifier)
HashSet(java.util.HashSet)
LinkedHashSet(java.util.LinkedHashSet)
Aggregations
Atom (at.ac.tuwien.kr.alpha.api.programs.atoms.Atom)1
ComparisonLiteral (at.ac.tuwien.kr.alpha.api.programs.literals.ComparisonLiteral)1
Literal (at.ac.tuwien.kr.alpha.api.programs.literals.Literal)1
DisjunctiveHead (at.ac.tuwien.kr.alpha.api.rules.heads.DisjunctiveHead)1
NormalHead (at.ac.tuwien.kr.alpha.api.rules.heads.NormalHead)1
Term (at.ac.tuwien.kr.alpha.api.terms.Term)1
VariableTerm (at.ac.tuwien.kr.alpha.api.terms.VariableTerm)1
Unifier (at.ac.tuwien.kr.alpha.commons.substitutions.Unifier)1
BasicRule (at.ac.tuwien.kr.alpha.core.rules.BasicRule)1
ArrayList (java.util.ArrayList)1
HashMap (java.util.HashMap)1
HashSet (java.util.HashSet)1
LinkedHashMap (java.util.LinkedHashMap)1
LinkedHashSet (java.util.LinkedHashSet)1
Map (java.util.Map)1
