001 /**
002 * Copyright 2005-2012 The Kuali Foundation
003 *
004 * Licensed under the Educational Community License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.opensource.org/licenses/ecl2.php
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016 package org.kuali.rice.krms.api.engine;
017
018 import java.util.Map;
019 import java.util.Set;
020
021 /**
022 * <p>An {@link TermResolver} implementor is a utility class used for resolution (reification) of {@link Term}s. There are a
023 * few key concepts to understand how {@link TermResolver}s function and work together.
024 * </p>
025 * <ul>
026 * <li><b>they can require prerequisite {@link Term}s (which must not have any parameters)</b>. If they do, when the {@link TermResolutionEngine} calls
027 * {@link #resolve(Map, Map)} it will pass the resolved prerequisites in the first argument.
028 * <li><b>they can be chained.</b> This means that if the {@link TermResolutionEngine} has {@link TermResolver}s (a <- b) and
029 * (b <- c), and you have the fact 'c', you can ask for term 'a' and the engine will chain the resolvers together
030 * to resolve it correctly.</li>
031 * <li><b>they can be parameterized.</b> If an TermResolver takes parameters, they must be declared via the
032 * {@link #getParameterNames()} method. All declared parameters are considered to be required. Parameters can be set
033 * on the {@link Term} (via the constructor) that you are asking to resolve. When the {@link TermResolutionEngine} calls
034 * {@link #resolve(Map, Map)}, the parameters will be passed in to the second argument.</li>
035 * <li><b>Parameterized {@link TermResolver}s can not be intermediates in a resolution plan.</b> Another way to say
036 * this is that they can only be the last resolver in a chain. For example, say
037 * the {@link TermResolutionEngine} has {@link TermResolver}s (a <- b) which takes no parameters,
038 * (b <- c) which takes a parameter "foo", and you have the fact 'c'. If you ask for Term 'a', the engine will not be able to resolve
039 * it because it would need to use a parameterized Term as an intermediate step in resolution, and that isn't allowed.</li>
040 *
041 * @author Kuali Rice Team (rice.collab@kuali.org)
042 *
043 * @param <T> the class of the resolved object
044 */
045 public interface TermResolver <T> {
046
047 /**
048 * @return the names of the terms that this resolver requires to resolve its output, or an empty set if it has no prereqs;
049 */
050 Set<String> getPrerequisites();
051
052 /**
053 * @return the name of the term that the implementor resolves
054 */
055 String getOutput();
056
057 /**
058 *
059 * @return the names of any parameters that this {@link TermResolver} requires to churn out values for multiple {@link Term}s. This may
060 * be null if no parameters are required. If this is non-null/non-empty, then this resolver can not be used as an intermediate
061 * in a term resolution chain.
062 */
063 Set<String> getParameterNames();
064
065 /**
066 * @return an integer representing the cost of resolving the term. 1 is cheap, Integer.MAX_INT is expensive.
067 */
068 int getCost();
069
070 /**
071 * @param resolvedPrereqs the resolved prereqs
072 * @param parameters any parameters on the {@link Term} to be resolved (which must match those declared via {@link #getParameterNames()}
073 * @return the resolved fact value for the specified {@link Term}
074 * @throws {@link TermResolutionException} if something bad happens during the term resolution process
075 */
076 T resolve(Map<String, Object> resolvedPrereqs, Map<String, String> parameters) throws TermResolutionException;
077 }