| 1 | package tuffy.mln; |
| 2 | import java.util.*; |
| 3 | |
| 4 | import tuffy.util.StringMan; |
| 5 | |
| 6 | /** |
| 7 | * A literal in first-order logic. |
| 8 | */ |
| 9 | public class Literal implements Cloneable { |
| 10 | |
| 11 | /** |
| 12 | * Predicate object associated with this literal. |
| 13 | */ |
| 14 | private Predicate pred; |
| 15 | |
| 16 | /** |
| 17 | * The index of this literal in its parent clause. |
| 18 | */ |
| 19 | private int idx = -1; |
| 20 | |
| 21 | /** |
| 22 | * List of terms (variable/constant) contained in this literal. |
| 23 | */ |
| 24 | private ArrayList<Term> terms = new ArrayList<Term>(); |
| 25 | |
| 26 | /** |
| 27 | * The positive/negative value of this literal. Here the positive/negative |
| 28 | * refers to that in Horn clause. |
| 29 | */ |
| 30 | private boolean sense; |
| 31 | |
| 32 | private boolean coversAllMaterializedTuples = false; |
| 33 | |
| 34 | /** |
| 35 | * The tuple format of this literal. Need call {@link Literal#toTuple()} to make |
| 36 | * this variable not null. This variable is not automatically maintained. |
| 37 | * To obtain the most update to date version, you need to call {@link Literal#toTuple()}. |
| 38 | */ |
| 39 | private Tuple tuple = null; |
| 40 | |
| 41 | /** |
| 42 | * The name set of all variables in this literal. |
| 43 | */ |
| 44 | private HashSet<String> vars = new HashSet<String>(); |
| 45 | |
| 46 | |
| 47 | @SuppressWarnings("unchecked") |
| 48 | public Object clone() throws CloneNotSupportedException { |
| 49 | |
| 50 | Literal clone=(Literal)super.clone(); |
| 51 | |
| 52 | // make the shallow copy of the object of type Department |
| 53 | clone.coversAllMaterializedTuples = coversAllMaterializedTuples; |
| 54 | clone.idx = -1; |
| 55 | clone.pred = pred; |
| 56 | clone.sense = sense; |
| 57 | clone.terms = (ArrayList<Term>) terms.clone(); |
| 58 | clone.tuple = tuple; |
| 59 | clone.vars = (HashSet<String>) vars.clone(); |
| 60 | return clone; |
| 61 | |
| 62 | } |
| 63 | |
| 64 | |
| 65 | /** |
| 66 | * Return whether the predicate of this literal is a built-in predicate. |
| 67 | */ |
| 68 | public boolean isBuiltIn(){ |
| 69 | return pred.isBuiltIn(); |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Constructor of Literal. |
| 74 | * |
| 75 | * @param predicate the predicate |
| 76 | * @param sense true for a positive literal; false for a negative one |
| 77 | */ |
| 78 | public Literal(Predicate predicate, boolean sense){ |
| 79 | this.sense = sense; |
| 80 | this.pred = predicate; |
| 81 | } |
| 82 | |
| 83 | /** |
| 84 | * Return the set of variable names in this literal. |
| 85 | */ |
| 86 | public HashSet<String> getVars(){ |
| 87 | return vars; |
| 88 | } |
| 89 | |
| 90 | /** |
| 91 | * Return the predicate of this literal. |
| 92 | */ |
| 93 | public Predicate getPred() { |
| 94 | return pred; |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * Return the list of terms in this literal. |
| 99 | */ |
| 100 | public ArrayList<Term> getTerms() { |
| 101 | return terms; |
| 102 | } |
| 103 | |
| 104 | /** |
| 105 | * Return the assigned index of this literal in its parent clause. |
| 106 | */ |
| 107 | public int getIdx() { |
| 108 | return idx; |
| 109 | } |
| 110 | |
| 111 | /** |
| 112 | * Assign an unique (within its parent clause) index to this literal. |
| 113 | * |
| 114 | * @param i the index |
| 115 | * @see Clause#addLiteral(Literal) |
| 116 | */ |
| 117 | public void setIdx(int i) { |
| 118 | idx = i; |
| 119 | } |
| 120 | |
| 121 | ///** |
| 122 | // * Clique of variables. |
| 123 | // * Used for the purpose of computing MGU. |
| 124 | // * |
| 125 | // * @see Literal#mostGeneralUnification(Tuple) |
| 126 | // */ |
| 127 | |
| 128 | /** |
| 129 | * Clique of variables. Here by clique, it means a set of |
| 130 | * variables, plus a constant. |
| 131 | * |
| 132 | * @see Literal#mostGeneralUnification(Tuple) |
| 133 | */ |
| 134 | private class VarClique{ |
| 135 | |
| 136 | /** |
| 137 | * The set of variable names in this clique. |
| 138 | */ |
| 139 | HashSet<String> vars = new HashSet<String>(); |
| 140 | |
| 141 | /** |
| 142 | * The constant of this clique. |
| 143 | */ |
| 144 | Integer constant = null; |
| 145 | |
| 146 | /** |
| 147 | * Add variable to this clique. |
| 148 | * @param v the name of added variable. |
| 149 | */ |
| 150 | public void addVar(String v) { |
| 151 | vars.add(v); |
| 152 | } |
| 153 | |
| 154 | /** |
| 155 | * Set the constant of this clique. This is allowed when |
| 156 | * 1) current constant is null; 2) current constant is |
| 157 | * equals to the changed constant. |
| 158 | * @param con the added constant. |
| 159 | * @return whether the intending setting is allowed and succeeded. |
| 160 | */ |
| 161 | public boolean setConstant(int con) { |
| 162 | if(constant != null && constant != con) { |
| 163 | return false; |
| 164 | } |
| 165 | constant = con; |
| 166 | return true; |
| 167 | } |
| 168 | |
| 169 | /** |
| 170 | * Merge a new clique with the current one. Here by merge, |
| 171 | * it requires the constant of these two cliques should be |
| 172 | * either null or the same. This process involves 1) merging the |
| 173 | * variable set and 2) check the consistency of constant. |
| 174 | * @param c the new clique |
| 175 | * @return whether the intending swallow is allowed and succeeded. |
| 176 | */ |
| 177 | public boolean swallow(VarClique c) { |
| 178 | if(constant != null && c.constant != null |
| 179 | && constant != c.constant) { |
| 180 | return false; |
| 181 | } |
| 182 | if(constant == null) { |
| 183 | constant = c.constant; |
| 184 | } |
| 185 | vars.addAll(c.vars); |
| 186 | return true; |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | /** |
| 191 | * Compute the most general unification (MGU) of two literals. |
| 192 | * |
| 193 | * @param atuple the literal (in the form of a tuple) to be unified |
| 194 | * @return the MGU in the form of a mapping from |
| 195 | * variables to variables/constants |
| 196 | */ |
| 197 | public HashMap<String, Term> mostGeneralUnification(Tuple atuple){ |
| 198 | Hashtable<String, VarClique> cliques = new Hashtable<String, VarClique>(); |
| 199 | int[] tuple = atuple.list; |
| 200 | for(int i=0; i<terms.size(); i++) { |
| 201 | Term t = terms.get(i); |
| 202 | if(t.isConstant()) { |
| 203 | // const-const map |
| 204 | if(tuple[i]>0 && t.constant() != tuple[i]) { |
| 205 | return null; |
| 206 | } |
| 207 | // const-var map |
| 208 | if(tuple[i] < 0) { |
| 209 | String var = Integer.toString(tuple[i]); |
| 210 | VarClique clique = cliques.get(var); |
| 211 | if(clique == null) { |
| 212 | clique = new VarClique(); |
| 213 | clique.addVar(var); |
| 214 | cliques.put(var, clique); |
| 215 | } |
| 216 | if(!clique.setConstant(t.constant())) { |
| 217 | return null; |
| 218 | } |
| 219 | } |
| 220 | }else { |
| 221 | VarClique clique1 = cliques.get(t.var()); |
| 222 | if(clique1 == null) { |
| 223 | clique1 = new VarClique(); |
| 224 | clique1.addVar(t.var()); |
| 225 | cliques.put(t.var(), clique1); |
| 226 | } |
| 227 | // var-const map |
| 228 | if(tuple[i] > 0) { |
| 229 | if(!clique1.setConstant(tuple[i])) { |
| 230 | return null; |
| 231 | } |
| 232 | }else { // var-var map |
| 233 | String var = Integer.toString(tuple[i]); |
| 234 | VarClique clique2 = cliques.get(var); |
| 235 | if(clique2 == null) { |
| 236 | clique2 = new VarClique(); |
| 237 | clique2.addVar(var); |
| 238 | cliques.put(var, clique2); |
| 239 | } |
| 240 | if(clique1.swallow(clique2)) { |
| 241 | for(String v : clique2.vars) { |
| 242 | cliques.put(v, clique1); |
| 243 | } |
| 244 | }else { |
| 245 | return null; |
| 246 | } |
| 247 | } |
| 248 | } |
| 249 | } |
| 250 | |
| 251 | HashMap<String, Term> lmap = new HashMap<String, Term>(); |
| 252 | for(String v : vars) { |
| 253 | VarClique clique = cliques.get(v); |
| 254 | Term t; |
| 255 | if(clique.constant == null) { |
| 256 | t = new Term(clique.toString()); |
| 257 | }else { |
| 258 | t = new Term(clique.constant); |
| 259 | } |
| 260 | lmap.put(v, t); |
| 261 | } |
| 262 | return lmap; |
| 263 | } |
| 264 | |
| 265 | /** |
| 266 | * Return the human-friendly representation of this literal. |
| 267 | */ |
| 268 | public String toString(){ |
| 269 | String s = (sense ? " " : "!"); |
| 270 | s += pred.getName(); |
| 271 | ArrayList<String> a = new ArrayList<String>(); |
| 272 | for(Term t : terms){ |
| 273 | if(t.isVariable()){ |
| 274 | a.add(t.var()); |
| 275 | }else{ |
| 276 | a.add("" + t.constant()); |
| 277 | } |
| 278 | } |
| 279 | s += StringMan.commaListParen(a); |
| 280 | return s; |
| 281 | } |
| 282 | |
| 283 | /** |
| 284 | * Append a new term to this literal. |
| 285 | * |
| 286 | * @param t the term to be appended |
| 287 | */ |
| 288 | public void appendTerm(Term t){ |
| 289 | terms.add(t); |
| 290 | if(t.isVariable()) { |
| 291 | vars.add(t.var()); |
| 292 | } |
| 293 | } |
| 294 | |
| 295 | /** |
| 296 | * Convert this literal into a tuple. This will assign an internal ID for |
| 297 | * variables obeying the syntax of class Tuple from Strings. |
| 298 | */ |
| 299 | public Tuple toTuple() { |
| 300 | if(tuple != null) return tuple; |
| 301 | ArrayList<Integer> tlist = new ArrayList<Integer>(); |
| 302 | Hashtable<String, Integer> varIDMap = new Hashtable<String, Integer>(); |
| 303 | for(Term t : terms) { |
| 304 | if(t.isConstant()) { |
| 305 | tlist.add(t.constant()); |
| 306 | }else { |
| 307 | String v = t.var(); |
| 308 | Integer id = varIDMap.get(v); |
| 309 | if(id == null) { |
| 310 | id = -(varIDMap.size()+1); |
| 311 | varIDMap.put(v, id); |
| 312 | } |
| 313 | tlist.add(id); |
| 314 | } |
| 315 | } |
| 316 | tuple = new Tuple(tlist); |
| 317 | return tuple; |
| 318 | } |
| 319 | |
| 320 | /** |
| 321 | * Compare a given literal with this one. By ``same'', it means |
| 322 | * 1) predicate is same; 2) sense is same; 3) corresponding constant |
| 323 | * is same; and 4) the name of corresponding variable is same. |
| 324 | * (Do not consider substitution). |
| 325 | * @param lit the literal needed to be compared. |
| 326 | * @return true if these two literals are the same, false otherwise. |
| 327 | */ |
| 328 | public boolean isSameAs(Literal lit){ |
| 329 | if(pred != lit.pred || sense != lit.sense) return false; |
| 330 | for(int i=0; i < terms.size(); i++){ |
| 331 | Term t1 = terms.get(i); |
| 332 | Term t2 = lit.terms.get(i); |
| 333 | if(t1.isConstant() != t2.isConstant()){ |
| 334 | return false; |
| 335 | } |
| 336 | if(t1.isConstant() && t1.constant() != t2.constant()){ |
| 337 | return false; |
| 338 | } |
| 339 | if(t1.isVariable() && !t1.var().equals(t2.var())){ |
| 340 | return false; |
| 341 | } |
| 342 | } |
| 343 | return true; |
| 344 | } |
| 345 | |
| 346 | /** |
| 347 | * Apply a substitution to this literal. |
| 348 | * |
| 349 | * @param vmap the substitution |
| 350 | * @return the new literal |
| 351 | */ |
| 352 | public Literal substitute(HashMap<String, Term> vmap) { |
| 353 | Literal copy = new Literal(pred, sense); |
| 354 | copy.coversAllMaterializedTuples = coversAllMaterializedTuples; |
| 355 | for(Term t : terms) { |
| 356 | if(t.isConstant()) { |
| 357 | copy.appendTerm(t); |
| 358 | }else { |
| 359 | Term t2 = vmap.get(t.var()); |
| 360 | if(t2 == null) { |
| 361 | copy.appendTerm(t); |
| 362 | }else { |
| 363 | copy.appendTerm(t2); |
| 364 | } |
| 365 | } |
| 366 | } |
| 367 | return copy; |
| 368 | } |
| 369 | |
| 370 | /** |
| 371 | * Convert this literal to an atom. |
| 372 | * |
| 373 | * @param type indicates if it's an evidence, a query, etc. |
| 374 | */ |
| 375 | public Atom toAtom(Atom.AtomType type){ |
| 376 | Atom a = new Atom(pred, this.toTuple()); |
| 377 | a.type = type; |
| 378 | return a; |
| 379 | } |
| 380 | |
| 381 | /** |
| 382 | * Flip the sense of this literal. |
| 383 | */ |
| 384 | public void flipSense(){ |
| 385 | sense = !sense; |
| 386 | } |
| 387 | |
| 388 | /** |
| 389 | * Return true if this is a positive literal. Here the positive/negative |
| 390 | * refers to that in Horn clause. |
| 391 | */ |
| 392 | public boolean getSense(){ |
| 393 | return sense; |
| 394 | } |
| 395 | |
| 396 | /** |
| 397 | * Set the sense of this literal. |
| 398 | * |
| 399 | * @param asense true if this is intended to be a positive literal |
| 400 | */ |
| 401 | public void setSense(boolean asense){ |
| 402 | sense = asense; |
| 403 | } |
| 404 | |
| 405 | /** |
| 406 | * Set whether we want this literal to cover all materialized tuples |
| 407 | * regardless of the sense of this literal. |
| 408 | * @param coversAllMaterializedTuples |
| 409 | */ |
| 410 | public void setCoversAllMaterializedTuples(boolean coversAllMaterializedTuples) { |
| 411 | this.coversAllMaterializedTuples = coversAllMaterializedTuples; |
| 412 | } |
| 413 | |
| 414 | /** |
| 415 | * Test whether we want this literal to cover all materialized tuples |
| 416 | * regardless of the sense of this literal. |
| 417 | */ |
| 418 | public boolean coversAllMaterializedTuples() { |
| 419 | return coversAllMaterializedTuples; |
| 420 | } |
| 421 | } |