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/* Copyright (C) 2013-2014 TU Dortmund
* This file is part of LearnLib, http://www.learnlib.de/.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package de.learnlib.api;
import java.util.Collection;
import javax.annotation.Nullable;
import javax.annotation.ParametersAreNonnullByDefault;
import net.automatalib.automata.fsa.DFA;
import net.automatalib.automata.transout.MealyMachine;
import net.automatalib.words.Word;
import de.learnlib.oracles.DefaultQuery;
/**
* An equivalence oracle, which checks hypothesis automata against the (possibly unknown)
* system under learning (SUL).
*
* Please note that equivalence oracles are implicitly connected to a SUL, there is no explicit
* references in terms of a {@link MembershipOracle} or such. However, this might be different
* in implementing classes.
*
* CAVEAT: Equivalence oracles serve as an abstraction to tackle the (generally undecidable)
* problem of black-box equivalence testing. The contract imposed by this interface is that
* results returned by the {@link #findCounterExample(Object, Collection)} method are in fact
* counterexamples, BUT a null result signalling no counterexample was found
* does not mean that there can be none.
*
* @author Maik Merten
* @author Malte Isberner
*
* @param automaton type this equivalence oracle works on
* @param input symbol type
* @param output domain type
*/
@ParametersAreNonnullByDefault
public interface EquivalenceOracle {
/**
* A specialization of the {@link EquivalenceOracle} interface for a DFA learning scenario.
*
* @author Malte Isberner
*
* @param input symbol class
*/
public static interface DFAEquivalenceOracle extends EquivalenceOracle,I,Boolean> {}
/**
* A specialization of the {@link EquivalenceOracle} interface for a Mealy learning scenario.
*
* @author Malte Isberner
*
* @param input symbol class
* @param output symbol class
*/
public static interface MealyEquivalenceOracle extends EquivalenceOracle,I,Word> {}
/**
* Searches for a counterexample disproving the subjected hypothesis.
* A counterexample is query which, when performed on the SUL, yields a different output
* than what was predicted by the hypothesis. If no counterexample could be found (this does
* not necessarily mean that none exists), null is returned.
*
* @param hypothesis the conjecture
* @param inputs the set of inputs to consider, this should be a subset of the input alphabet
* of the provided hypothesis
* @return a query exposing different behavior, or null if no counterexample
* could be found. In case a non-null value is returned, the output field
* in the {@link DefaultQuery} contains the SUL output for the respective query.
*/
@Nullable
public DefaultQuery findCounterExample(A hypothesis, Collection inputs);
}