ValidityResult.java

/*******************************************************************************
 * Copyright (c) 2013 Stephen F. Siegel, University of Delaware.
 * 
 * This file is part of SARL.
 * 
 * SARL is free software: you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 * 
 * SARL is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with SARL. If not, see <http://www.gnu.org/licenses/>.
 ******************************************************************************/
package edu.udel.cis.vsl.sarl.IF;

/**
 * <p>
 * A {@link ValidityResult} represents the result of a validity query.
 * </p>
 * 
 * <p>
 * It defines an enumerated type {@link ResultType} with three possible values:
 * {@link ResultType#YES}, {@link ResultType#NO}, {@link ResultType#MAYBE}. This
 * is used to represent the result returned by an automated theorem prover.
 * </p>
 * 
 * <p>
 * In the case that the result type is {@link ResultType#NO}, a
 * {@link ValidityResult} may also provide a <i>model</i>, i.e., an assignment
 * of concrete values to symbolic constants that leads the assumption to
 * evaluate to <code>true</code> and the predicate to evaluate to
 * <code>false</code>.
 * </p>
 * 
 * <p>
 * The subclass {@link ModelResult} provides a method to get a model
 * (counterexample). A {@link ModelResult} always has result type
 * {@link ResultType#NO}, because only invalid queries can have models. However,
 * the model returned may be <code>null</code>: this indicates that the attempt
 * to find a model failed for some reason.
 * </p>
 * 
 * <p>
 * An instance of {@link ValidityResult} of type {@link ResultType#NO} that is
 * not an instance of {@link ModelResult} indicates that there was no attempt to
 * find a model.
 * </p>
 * 
 * @author Stephen F. Siegel
 */
public interface ValidityResult {

	/**
	 * The 3 kinds of results to the "valid" question: yes, no, or maybe (a.k.a,
	 * "I don't know").
	 * 
	 */
	public enum ResultType {
		/** Yes, the predicate is valid under the given context */
		YES,
		/** No, the predicate is not valid under the given context */
		NO,
		/** Nothing can be concluded about the validity of the query */
		MAYBE
	};

	/**
	 * Returns the result type of this result.
	 * 
	 * @return the result type
	 */
	public ResultType getResultType();

}