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Additional constraint generated during transformation of choice rules #282

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Additional constraint generated during transformation of choice rules #282

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16 changes: 11 additions & 5 deletions src/main/java/at/ac/tuwien/kr/alpha/grounder/transformation/ChoiceHeadToNormal.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/**
* Copyright (c) 2017-2018, the Alpha Team.
/*
* Copyright (c) 2017-2020, the Alpha Team.
* All rights reserved.
*
* Additional changes made by Siemens.
Expand Down Expand Up @@ -79,7 +79,7 @@ public InputProgram apply(InputProgram inputProgram) {
for (ChoiceHead.ChoiceElement choiceElement : choiceHead.getChoiceElements()) {
// Create two guessing rules for each choiceElement.

// Construct common body to both rules.
// Construct body common to both rules and constraint.
Atom head = choiceElement.choiceAtom;
List<Literal> ruleBody = new ArrayList<>(rule.getBody());
ruleBody.addAll(choiceElement.conditionLiterals);
Expand All @@ -99,13 +99,19 @@ public InputProgram apply(InputProgram inputProgram) {

// Construct two guessing rules.
List<Literal> guessingRuleBodyWithNegHead = new ArrayList<>(ruleBody);
guessingRuleBodyWithNegHead.add(new BasicAtom(head.getPredicate(), head.getTerms()).toLiteral(false));
guessingRuleBodyWithNegHead.add(head.toLiteral(false));
additionalRules.add(new BasicRule(new NormalHead(negHead), guessingRuleBodyWithNegHead));

List<Literal> guessingRuleBodyWithHead = new ArrayList<>(ruleBody);
guessingRuleBodyWithHead.add(new BasicAtom(negPredicate, headTerms).toLiteral(false));
guessingRuleBodyWithHead.add(negHead.toLiteral(false));
additionalRules.add(new BasicRule(new NormalHead(head), guessingRuleBodyWithHead));

// Construct a constraint: complementary atoms may not be true simultaneously.
List<Literal> bodyOfConstraint = new ArrayList<>(ruleBody);
bodyOfConstraint.add(head.toLiteral());
bodyOfConstraint.add(negHead.toLiteral());
additionalRules.add(new BasicRule(null, bodyOfConstraint));

// TODO: when cardinality constraints are possible, process the boundaries by adding a constraint with a cardinality check.
}
}
Expand Down
3 changes: 3 additions & 0 deletions src/test/resources/transform-test/choice-to-normal.1.out
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Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
_nred("1", N) :- node(N), not red(N).
red(N) :- node(N), not _nred("1", N).
:- node(N), red(N), _nred("1", N).
_ngreen("1", N) :- node(N), not green(N).
green(N) :- node(N), not _ngreen("1", N).
:- node(N), green(N), _ngreen("1", N).
_nblue("1", N) :- node(N), not blue(N).
blue(N) :- node(N), not _nblue("1", N).
:- node(N), blue(N), _nblue("1", N).