1 /**
2 * Copyright 2005-2012 The Kuali Foundation
3 *
4 * Licensed under the Educational Community License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.opensource.org/licenses/ecl2.php
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package org.kuali.rice.krms.api.engine;
17
18 import java.util.Map;
19 import java.util.Set;
20
21 /**
22 * <p>An {@link TermResolver} implementor is a utility class used for resolution (reification) of fact values for one or
23 * more{@link Term}s. There are a few key concepts to understand how {@link TermResolver}s function and work together.
24 * </p>
25 * <ul>
26 * <li><b>they can require prerequisite {@link Term}s</b> (which must not have any parameters). If they do, when the {@link TermResolutionEngine} calls
27 * {@link #resolve(Map, Map)} it will pass the resolved prerequisites in the first argument.
28 * <li><b>they can be chained.</b> This means that if the {@link TermResolutionEngine} has {@link TermResolver}s (a <- b) and
29 * (b <- c), and you have the fact 'c', you can ask for term 'a' and the engine will chain the resolvers together
30 * to resolve it correctly.</li>
31 * <li><b>they can be parameterized.</b> If an TermResolver takes parameters, they must be declared via the
32 * {@link #getParameterNames()} method. All declared parameters are considered to be required. Parameters can be set
33 * on the {@link Term} (via the constructor) that you are asking to resolve. When the {@link TermResolutionEngine} calls
34 * {@link #resolve(Map, Map)}, the parameters will be passed in to the second argument.</li>
35 * <li><b>Parameterized {@link TermResolver}s can not be intermediates in a resolution plan.</b> Another way to say
36 * this is that they can only be the last resolver in a chain. For example, say
37 * the {@link TermResolutionEngine} has {@link TermResolver}s (a <- b) which takes no parameters,
38 * (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
39 * it because it would need to use a parameterized Term as an intermediate step in resolution, and that isn't allowed.</li>
40 *
41 * @author Kuali Rice Team (rice.collab@kuali.org)
42 *
43 * @param <T> the class of the resolved object
44 */
45 public interface TermResolver <T> {
46
47 /**
48 * Gets the names of the terms that this resolver requires in order to be able to resolve its output,
49 * or an empty set if it has no prereqs;
50 *
51 * @return the prerequisite term names
52 */
53 Set<String> getPrerequisites();
54
55 /**
56 * Gets the name of the term that this TermResolver resolves.
57 *
58 * @return the name of the term this TermResolver resolves.
59 */
60 String getOutput();
61
62 /**
63 * Gets the names of any parameters that this {@link TermResolver} requires to resolve {@link Term}s.
64 * This may be null if no parameters are required. If this is non-null/non-empty, then this
65 * resolver can not be used as an intermediate in a term resolution chain.
66 *
67 * @return the names of parameters this TermResolver requires for resolution.
68 */
69 Set<String> getParameterNames();
70
71 /**
72 * Gets an int representing the cost of resolving the term. 1 is cheap, Integer.MAX_INT is expensive.
73 *
74 * @return the cost.
75 */
76 int getCost();
77
78 /**
79 * Resolves the output term's fact value given the resolved prerequisite terms and term parameters. The term
80 * resolution engine will call this method providing the following parameters to the resolver:
81 *
82 * @param resolvedPrereqs the resolved prereqs. May be empty, but never null.
83 * @param parameters any parameters on the {@link Term} to be resolved (which must match those declared via
84 * {@link #getParameterNames()}. May be empty, but never null.
85 * @return the resolved fact value for the specified {@link Term}. May be null.
86 * @throws {@link TermResolutionException} if something bad happens during the term resolution process.
87 */
88 T resolve(Map<String, Object> resolvedPrereqs, Map<String, String> parameters) throws TermResolutionException;
89 }