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A library for incremental automata construction. This artifact contains algorithms for incrementally
constructing DFAs (prefix-closed and non-prefix-closed), Mealy machines, and Moore machines from a finite,
incrementally growing set of example inputs/outputs.
/* Copyright (C) 2013-2020 TU Dortmund
* This file is part of AutomataLib, http://www.automatalib.net/.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.automatalib.incremental.dfa.dag;
import java.util.ArrayDeque;
import java.util.Deque;
import net.automatalib.incremental.ConflictException;
import net.automatalib.incremental.dfa.Acceptance;
import net.automatalib.words.Alphabet;
import net.automatalib.words.Word;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Incrementally builds an (acyclic) DFA, from a set of positive and negative words. Using {@link #insert(Word,
* boolean)}, either the set of words definitely in the target language or definitely not in the target language
* is augmented. The {@link #lookup(Word)} method then returns, for a given word, whether this word is in the set of
* definitely accepted words ({@link Acceptance#TRUE}), definitely rejected words ({@link Acceptance#FALSE}), or neither
* ({@link Acceptance#DONT_KNOW}).
*
* @param
* input symbol class
*
* @author Malte Isberner
*/
public class IncrementalDFADAGBuilder extends AbstractIncrementalDFADAGBuilder {
/**
* Constructor. Initializes the incremental builder.
*
* @param inputAlphabet
* the input alphabet to use
*/
public IncrementalDFADAGBuilder(Alphabet inputAlphabet) {
super(inputAlphabet);
}
/**
* Checks the ternary acceptance status for a given word.
*
* @param word
* the word to check
*
* @return the acceptance status for the given word
*/
@Override
public Acceptance lookup(Word word) {
State s = getState(word);
if (s == null) {
return Acceptance.DONT_KNOW;
}
return s.getAcceptance();
}
/**
* Inserts a word into either the set of accepted or rejected words.
*
* @param word
* the word to insert
* @param accepting
* whether to insert this word into the set of accepted or rejected words.
*/
@Override
public void insert(Word word, boolean accepting) {
int len = word.length();
Acceptance acc = Acceptance.fromBoolean(accepting);
State curr = init;
State conf = null;
Deque path = new ArrayDeque<>();
for (I sym : word) {
if (conf == null && curr.isConfluence()) {
conf = curr;
}
int idx = inputAlphabet.getSymbolIndex(sym);
State succ = curr.getSuccessor(idx);
if (succ == null) {
break;
}
path.push(new PathElem(curr, idx));
curr = succ;
}
int prefixLen = path.size();
State last = curr;
if (prefixLen == len) {
// structural skeleton for this word already present
Acceptance currAcc = curr.getAcceptance();
if (currAcc == acc) {
// consistent with our existing knowledge, nothing changes
return;
}
if (currAcc != Acceptance.DONT_KNOW) {
// conflict
throw new ConflictException("Incompatible acceptances: " + currAcc + " vs " + acc);
}
if (conf != null || last.isConfluence()) {
// there is a confluence (maybe in the last node), so duplicate
// the last node (this will have to be propagated)
last = clone(last, acc);
} else if (last == init) {
// we inserted the empty word, so update the acceptance of the initial
// state (nothing else changes)
updateInitSignature(acc);
return;
} else {
// no confluence, so just update the signature
last = updateSignature(last, acc);
}
} else {
// we had to abort after processing a prefix
if (conf != null) {
if (conf == last) {
// if the first confluence is the last node, this confluence gets resolved
// directly by cloning (so act as if there was no confluence)
conf = null;
}
// confluence always requires cloning, to separate this path from other paths
last = hiddenClone(last);
if (conf == null) {
PathElem peek = path.peek();
assert peek != null;
State prev = peek.state;
if (prev != init) {
updateSignature(prev, peek.transIdx, last);
} else {
updateInitSignature(peek.transIdx, last);
}
}
} else if (last != init) {
hide(last);
}
@SuppressWarnings("assignment.type.incompatible") // TODO maybe properly enforce @KeyFor(this)?
Word suffix = word.subWord(prefixLen);
I sym = suffix.firstSymbol();
int suffTransIdx = inputAlphabet.getSymbolIndex(sym);
State suffixState = createSuffix(suffix.subWord(1), acc);
if (last != init) {
last = unhide(last, suffTransIdx, suffixState);
} else {
updateInitSignature(suffTransIdx, suffixState);
}
}
if (path.isEmpty()) {
return;
}
if (conf != null) {
PathElem next;
do {
next = path.pop();
State state = next.state;
int idx = next.transIdx;
state = clone(state, idx, last);
last = state;
} while (next.state != conf);
}
while (path.size() > 1) {
PathElem next = path.pop();
State state = next.state;
int idx = next.transIdx;
State updated = updateSignature(state, idx, last);
if (state == updated) {
return;
}
last = updated;
}
int finalIdx = path.pop().transIdx;
updateInitSignature(finalIdx, last);
}
/**
* Creates a suffix state sequence, i.e., a linear sequence of states connected by transitions labeled by the
* letters of the given suffix word.
*
* @param suffix
* the suffix word
* @param acc
* the acceptance status of the final state
*
* @return the first state in the sequence
*/
private State createSuffix(Word suffix, Acceptance acc) {
StateSignature sig = new StateSignature(alphabetSize, acc);
sig.updateHashCode();
State last = replaceOrRegister(sig);
int len = suffix.length();
for (int i = len - 1; i >= 0; i--) {
sig = new StateSignature(alphabetSize, Acceptance.DONT_KNOW);
I sym = suffix.getSymbol(i);
int idx = inputAlphabet.getSymbolIndex(sym);
sig.successors.array[idx] = last;
sig.updateHashCode();
last = replaceOrRegister(sig);
}
return last;
}
/**
* Retrieves the state reached by a given word.
*
* @param word
* the word
*
* @return the state reached by the given word, or {@code null} if no state is reachable by that word
*/
@Override
protected @Nullable State getState(Word word) {
State s = init;
for (I sym : word) {
int idx = inputAlphabet.getSymbolIndex(sym);
s = s.getSuccessor(idx);
if (s == null) {
return null;
}
}
return s;
}
}