/*______________________________________________________________________________ * * Copyright 2005 Arnaud Bailly - NORSYS/LIFL * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * (1) Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * (2) Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * (3) The name of the author may not be used to endorse or promote * products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. * * Created on 20 fevr. 2005 * */ package rationals.transformations; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import rationals.Automaton; import rationals.NoSuchStateException; import rationals.State; import rationals.Transition; /** * This class computes the projection of an Automaton on given alphabet. The * projection alphabet is set by the class's constructor. * <p /> * The algorithm is verys simple: All transitions which are not labelled * with letters from the projection alphabet are transformed into * <code>null</code> transitions. The resulting automaton is obviously no * more deterministic if the automaton <code>a</code> was. * * @author nono * @version $Id: Projection.java 2 2006-08-24 14:41:48Z oqube $ */ public class Projection implements UnaryTransformation { private Set alphabet; public Projection(Set alphabet) { this.alphabet = alphabet; } /* * (non-Javadoc) * * @see rationals.transformations.UnaryTransformation#transform(rationals.Automaton) */ public Automaton transform(Automaton a) { Automaton b = new Automaton(); Map smap = new HashMap(); Iterator it = a.delta().iterator(); while (it.hasNext()) { Transition tr = (Transition) it.next(); State os = tr.start(); State oe = tr.end(); Object l = tr.label(); /* check states exist */ State ns = (State) smap.get(os); State ne = (State) smap.get(oe); if (ns == null) smap.put(os, ns = b.addState(os.isInitial(), os.isTerminal())); if (ne == null) smap.put(oe, ne = b.addState(oe.isInitial(), oe.isTerminal())); /* check label is in alphabet */ if (alphabet.contains(l)) try { b.addTransition(new Transition(ns, l, ne)); } catch (NoSuchStateException e) { } else try { b.addTransition(new Transition(ns, null, ne)); } catch (NoSuchStateException e1) { } } return b; } }