/*______________________________________________________________________________
*
* 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;
}
}