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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 javax.annotation.Nonnull;

import net.automatalib.automata.fsa.DFA;
import net.automatalib.automata.transout.MealyMachine;
import net.automatalib.words.Word;
import de.learnlib.oracles.DefaultQuery;



/**
 * Basic interface for a model inference algorithm.
 * 
 * Actively inferring models (such as DFAs or Mealy machines) consists of the construction
 * of an initial hypothesis, which is subsequently refined using counterexamples
 * (see {@link EquivalenceOracle}). 
 * 
 * @author Maik Merten
 * @author Malte Isberner
 *
 * @param  model type
 * @param  input symbol type
 * @param  output domain type
 */
public interface LearningAlgorithm {
	
	static interface DFALearner extends LearningAlgorithm,I,Boolean> {}
	static interface MealyLearner extends LearningAlgorithm,I,Word> {}
	
	/**
	 * Starts the model inference process, creating an initial hypothesis in the provided
	 * model object. Please note that it should be illegal to invoke this method twice.
	 */
	void startLearning();
	
	/**
	 * Triggers a refinement of the model by providing a counterexample.
	 * A counterexample is a query which exposes different behavior of the real SUL compared
	 * to the hypothesis. Please note that invoking this method before an initial
	 * invocation of {@link #startLearning()} should be illegal.
	 * 
	 * @param ceQuery the query which exposes diverging behavior, as posed to the real SUL
	 * (i.e. with the SULs output).
	 * @return true if the counterexample triggered a refinement of the hypothesis,
	 * false otherwise (i.e., it was no counterexample).
	 */
	public boolean refineHypothesis(@Nonnull DefaultQuery ceQuery);

	
	/**
	 * Returns the current hypothesis model.
	 * 

	 * N.B.: By the contract of this interface, the model returned by this method may not be
	 * modified (i.e., M generally should refer to an immutable interface), and its validity
	 * is retained only until the next invocation of {@link #refineHypothesis(DefaultQuery)}. If
	 * older hypotheses have to be maintained, a copy of the returned model must be made.
	 * 
	 * Please note that it should be illegal to invoke this method before an initial invocation
	 * of {@link #startLearning()}.
	 * @return the current hypothesis model.
	 */
	@Nonnull
	public M getHypothesisModel();
}