/**
* Copyright (C) 2013 Christian Kohlschütter (ckkohl79@gmail.com)
*
* 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 de.l3s.boilerpipe.filters.english;
import java.util.List;
import java.util.ListIterator;
import de.l3s.boilerpipe.BoilerpipeFilter;
import de.l3s.boilerpipe.BoilerpipeProcessingException;
import de.l3s.boilerpipe.document.TextBlock;
import de.l3s.boilerpipe.document.TextDocument;
/**
* Classifies {@link TextBlock}s as content/not-content through rules that have
* been determined using the C4.8 machine learning algorithm, as described in the
* paper "Boilerplate Detection using Shallow Text Features", particularly using
* text densities and link densities.
*
* @author Christian Kohlschütter
*/
public class DensityRulesClassifier implements
BoilerpipeFilter {
public static final DensityRulesClassifier INSTANCE = new DensityRulesClassifier();
/**
* Returns the singleton instance for RulebasedBoilerpipeClassifier.
*/
public static DensityRulesClassifier getInstance() {
return INSTANCE;
}
public boolean process(TextDocument doc)
throws BoilerpipeProcessingException {
List<TextBlock> textBlocks = doc.getTextBlocks();
boolean hasChanges = false;
ListIterator<TextBlock> it = textBlocks.listIterator();
if (!it.hasNext()) {
return false;
}
TextBlock prevBlock = TextBlock.EMPTY_START;
TextBlock currentBlock = it.next();
TextBlock nextBlock = it.hasNext() ? it.next() : TextBlock.EMPTY_START;
hasChanges = classify(prevBlock, currentBlock, nextBlock) | hasChanges;
if (nextBlock != TextBlock.EMPTY_START) {
while (it.hasNext()) {
prevBlock = currentBlock;
currentBlock = nextBlock;
nextBlock = it.next();
hasChanges = classify(prevBlock, currentBlock, nextBlock)
| hasChanges;
}
prevBlock = currentBlock;
currentBlock = nextBlock;
nextBlock = TextBlock.EMPTY_START;
hasChanges = classify(prevBlock, currentBlock, nextBlock)
| hasChanges;
}
return hasChanges;
}
protected boolean classify(final TextBlock prev, final TextBlock curr,
final TextBlock next) {
final boolean isContent;
if (curr.getLinkDensity() <= 0.333333) {
if (prev.getLinkDensity() <= 0.555556) {
if (curr.getTextDensity() <= 9) {
if (next.getTextDensity() <= 10) {
if (prev.getTextDensity() <= 4) {
isContent = false;
} else {
isContent = true;
}
} else {
isContent = true;
}
} else {
if (next.getTextDensity() == 0) {
isContent = false;
} else {
isContent = true;
}
}
} else {
if (next.getTextDensity() <= 11) {
isContent = false;
} else {
isContent = true;
}
}
} else {
isContent = false;
}
return curr.setIsContent(isContent);
}
}