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diff --git a/Solvers/VIATRA-Solver/org.eclipse.viatra.dse/src/org/eclipse/viatra/dse/objectives/IObjective.java b/Solvers/VIATRA-Solver/org.eclipse.viatra.dse/src/org/eclipse/viatra/dse/objectives/IObjective.java
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+++ b/Solvers/VIATRA-Solver/org.eclipse.viatra.dse/src/org/eclipse/viatra/dse/objectives/IObjective.java
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+/*******************************************************************************
+ * Copyright (c) 2010-2014, Miklos Foldenyi, Andras Szabolcs Nagy, Abel Hegedus, Akos Horvath, Zoltan Ujhelyi and Daniel Varro
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package org.eclipse.viatra.dse.objectives;
+
+import java.util.Comparator;
+
+import org.eclipse.viatra.dse.base.ThreadContext;
+
+/**
+ * 
+ * Implementation of this interface represents a single objective of the DSE problem, which can assess a solution
+ * (trajectory) in a single number. It has a name and a comparator which orders two solution based on the calculated
+ * value.
+ * <p>
+ * Objectives can be either hard or soft objectives. Hard objectives can be satisfied or unsatisfied. If all of the hard
+ * objectives are satisfied on a single solution, then it is considered to be a valid (or goal) solution.
+ * <p>
+ * Certain objectives can have inner state for calculating the fitness value. In this case a new instance is necessary
+ * for every new thread, and the {@code createNew} method should not return the same instance more than once.
+ * 
+ * @author Andras Szabolcs Nagy
+ *
+ */
+public interface IObjective {
+
+    /**
+     * Returns the name of the objective.
+     * 
+     * @return The name of the objective.
+     */
+    String getName();
+
+    /**
+     * Sets the {@link Comparator} which is used to compare fitness (doubles). It determines whether the objective is to
+     * minimize or maximize (or minimize or maximize a delta from a given number).
+     * 
+     * @param comparator The comparator.
+     */
+    void setComparator(Comparator<Double> comparator);
+
+    /**
+     * Returns a {@link Comparator} which is used to compare fitness (doubles). It determines whether the objective is
+     * to minimize or maximize (or minimize or maximize a delta from a given number).
+     * 
+     * @return The comparator.
+     */
+    Comparator<Double> getComparator();
+
+    /**
+     * Calculates the value of the objective on a given solution (trajectory).
+     * 
+     * @param context
+     *            The {@link ThreadContext}
+     * @return The objective value in double.
+     */
+    Double getFitness(ThreadContext context);
+
+    /**
+     * Initializes the objective. It is called exactly once for every thread starts.
+     * 
+     * @param context
+     *            The {@link ThreadContext}.
+     */
+    void init(ThreadContext context);
+
+    /**
+     * Returns an instance of the {@link IObjective}. If it returns the same instance, all the methods has to be thread
+     * save as they are called concurrently.
+     * 
+     * @return An instance of the objective.
+     */
+    IObjective createNew();
+
+    /**
+     * Returns true if the objective is a hard objective. In such a case the method
+     * {@link IObjective#satisifiesHardObjective(Double)} is called.
+     * 
+     * @return True if the objective is a hard objective.
+     * @see IObjective#satisifiesHardObjective(Double)
+     * @see IObjective
+     */
+    boolean isHardObjective();
+
+    /**
+     * Determines if the given fitness value satisfies the hard objective.
+     * 
+     * @param fitness
+     *            The fitness value of a solution.
+     * @return True if it satisfies the hard objective or it is a soft constraint.
+     * @see IObjective
+     */
+    boolean satisifiesHardObjective(Double fitness);
+
+    /**
+     * Set the level of the objective.
+     */
+    void setLevel(int level);
+
+    /**
+     * Gets the level of the objective.
+     */
+    int getLevel();
+
+}