001 /*
002 * Created on Sep 2, 2003 by Ravi Mohan
003 *
004 */
005 package aima.logic.propositional.algorithms;
006
007 import java.util.HashSet;
008 import java.util.Hashtable;
009 import java.util.Iterator;
010 import java.util.Set;
011
012 import aima.logic.propositional.parsing.PLVisitor;
013 import aima.logic.propositional.parsing.ast.BinarySentence;
014 import aima.logic.propositional.parsing.ast.FalseSentence;
015 import aima.logic.propositional.parsing.ast.MultiSentence;
016 import aima.logic.propositional.parsing.ast.Sentence;
017 import aima.logic.propositional.parsing.ast.Symbol;
018 import aima.logic.propositional.parsing.ast.TrueSentence;
019 import aima.logic.propositional.parsing.ast.UnarySentence;
020
021 /**
022 * @author Ravi Mohan
023 *
024 */
025
026 public class Model implements PLVisitor {
027
028 Hashtable<String, Boolean> h = new Hashtable<String, Boolean>();
029
030 public Boolean getStatus(Symbol symbol) {
031 Object status = h.get(symbol.getValue());
032 if (status != null) {
033 return (Boolean) status;
034 }
035 return null;
036 }
037
038 public boolean isTrue(Symbol symbol) {
039 Object status = h.get(symbol.getValue());
040 if (status != null) {
041 return ((Boolean) status).booleanValue();
042 }
043 return false;
044 }
045
046 public boolean isFalse(Symbol symbol) {
047 Object status = h.get(symbol.getValue());
048 if (status != null) {
049 return !((Boolean) status).booleanValue();
050 }
051 return false;
052 }
053
054 private boolean isUnknown(Symbol s) {
055 Object o = h.get(s.getValue());
056 return (o == null);
057
058 }
059
060 public Model extend(Symbol symbol, boolean b) {
061 Model m = new Model();
062 return extend(symbol.getValue(), b);
063 }
064
065 public Model extend(String s, boolean b) {
066 Model m = new Model();
067 Iterator<String> i = this.h.keySet().iterator();
068 while (i.hasNext()) {
069 String key = i.next();
070 Boolean value = h.get(key);
071 String newKey = new String((key).toCharArray());
072 if (value == null) {
073 throw new RuntimeException();
074 }
075 m.h.put(key, value);
076 }
077 m.h.put(s, new Boolean(b));
078 return m;
079 }
080
081 public void print() {
082 Iterator i = h.keySet().iterator();
083 while (i.hasNext()) {
084 Object key = i.next();
085 Object value = h.get(key);
086 System.out.print(key + " = " + value + " ");
087 // System.out.print (key +" = " +((Boolean)value).booleanValue());
088 }
089 System.out.println();
090 }
091
092 public boolean isTrue(Sentence clause) {
093 Object result = clause.accept(this, null);
094 return (result == null) ? false
095 : ((Boolean) result).booleanValue() == true;
096 }
097
098 public boolean isFalse(Sentence clause) {
099 Object o = clause.accept(this, null);
100 return (o != null) ? ((Boolean) o).booleanValue() == false : false;
101 }
102
103 public boolean isUnknown(Sentence clause) { // TODO TEST WELL
104 Object o = clause.accept(this, null);
105 return (o == null);
106 }
107
108 public Model flip(Symbol s) {
109 if (isTrue(s)) {
110 return extend(s, false);
111 }
112 if (isFalse(s)) {
113 return extend(s, true);
114 }
115 return this;
116 }
117
118 @Override
119 public String toString() {
120 return h.toString();
121 }
122
123 // VISITOR METHODS
124 public Object visitSymbol(Symbol s, Object arg) {
125 return getStatus(s);
126 }
127
128 public Object visitTrueSentence(TrueSentence ts, Object arg) {
129 return Boolean.TRUE;
130 }
131
132 public Object visitFalseSentence(FalseSentence fs, Object arg) {
133 return Boolean.FALSE;
134 }
135
136 public Object visitNotSentence(UnarySentence fs, Object arg) {
137 Object negatedValue = fs.getNegated().accept(this, null);
138 if (negatedValue != null) {
139 return new Boolean(!((Boolean) negatedValue).booleanValue());
140 } else {
141 return null;
142 }
143 }
144
145 public Object visitBinarySentence(BinarySentence bs, Object arg) {
146 Object firstValue = bs.getFirst().accept(this, null);
147 Object secondValue = bs.getSecond().accept(this, null);
148 if ((firstValue == null) || (secondValue == null)) { // strictly not
149 // true for or/and
150 // -FIX later
151 return null;
152 } else {
153 String operator = bs.getOperator();
154 if (operator.equals("AND")) {
155 return evaluateAnd((Boolean) firstValue, (Boolean) secondValue);
156 }
157 if (operator.equals("OR")) {
158 return evaluateOr((Boolean) firstValue, (Boolean) secondValue);
159 }
160 if (operator.equals("=>")) {
161 return evaluateImplied((Boolean) firstValue,
162 (Boolean) secondValue);
163 }
164 if (operator.equals("<=>")) {
165 return evaluateBiConditional((Boolean) firstValue,
166 (Boolean) secondValue);
167 }
168 return null;
169 }
170 }
171
172 public Object visitMultiSentence(MultiSentence fs, Object argd) {
173 // TODO remove this?
174 return null;
175 }
176
177 private Boolean evaluateAnd(Boolean firstValue, Boolean secondValue) {
178 if ((firstValue.equals(Boolean.TRUE))
179 && (secondValue.equals(Boolean.TRUE))) {
180 return Boolean.TRUE;
181 } else {
182 return Boolean.FALSE;
183 }
184 }
185
186 private Boolean evaluateOr(Boolean firstValue, Boolean secondValue) {
187 if ((firstValue.equals(Boolean.TRUE))
188 || (secondValue.equals(Boolean.TRUE))) {
189 return Boolean.TRUE;
190 } else {
191 return Boolean.FALSE;
192 }
193 }
194
195 private Boolean evaluateImplied(Boolean firstValue, Boolean secondValue) {
196 if ((firstValue.equals(Boolean.TRUE))
197 && (secondValue.equals(Boolean.FALSE))) {
198 return Boolean.FALSE;
199 } else {
200 return Boolean.TRUE;
201 }
202 }
203
204 private Boolean evaluateBiConditional(Boolean firstValue,
205 Boolean secondValue) {
206 if (firstValue.equals(secondValue)) {
207 return Boolean.TRUE;
208 } else {
209 return Boolean.FALSE;
210 }
211 }
212
213 public Set<Symbol> getAssignedSymbols() {
214 Set<Symbol> set = new HashSet<Symbol>();
215 Iterator i = this.h.keySet().iterator();
216 while (i.hasNext()) {
217 Symbol key = new Symbol((String) i.next());
218 if (!(isUnknown(key))) {
219 set.add(key);
220 }
221 }
222 return set;
223 }
224
225 public boolean matches(String variable, boolean value) {
226 if (value) {
227 return isTrue(new Symbol(variable));
228 } else if (!(value)) {
229 return isFalse(new Symbol(variable));
230 }
231 return false;
232 }
233
234 }