Training models using openNLP maxent

Question

I have gold data where I annotated all room numbers from several documents. I want to use openNLP to train a model that uses this data and classify room numbers. I am stuck

Answer 1

This is a minimal working example that demonstrates the usage of OpenNLP Maxent API.

It includes the following:

• Training a maxent model from data stored in a file.
• Storing the trained model into a file.
• Loading the trained model from a file.
• Using the model for classification.
• NOTE: the outcome is the first element in each training sample
• NOTE: the values can be arbitrary strings, e.g. xyz=s0methIng

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import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;

import opennlp.maxent.GIS;
import opennlp.maxent.io.GISModelReader;
import opennlp.maxent.io.SuffixSensitiveGISModelWriter;
import opennlp.model.AbstractModel;
import opennlp.model.AbstractModelWriter;
import opennlp.model.DataIndexer;
import opennlp.model.DataReader;
import opennlp.model.FileEventStream;
import opennlp.model.MaxentModel;
import opennlp.model.OnePassDataIndexer;
import opennlp.model.PlainTextFileDataReader;

...

String trainingFileName = "training-file.txt";
String modelFileName = "trained-model.maxent.gz";

// Training a model from data stored in a file.
// The training file contains one training sample per line.
// Outcome (result) is the first element on each line.
// Example:
// result=1 a=1 b=1
// result=0 a=0 b=1
// ...
DataIndexer indexer = new OnePassDataIndexer( new FileEventStream(trainingFileName)); 
MaxentModel trainedMaxentModel = GIS.trainModel(100, indexer); // 100 iterations

// Storing the trained model into a file for later use (gzipped)
File outFile = new File(modelFileName);
AbstractModelWriter writer = new SuffixSensitiveGISModelWriter((AbstractModel) trainedMaxentModel, outFile);
writer.persist();

// Loading the gzipped model from a file
FileInputStream inputStream = new FileInputStream(modelFileName);
InputStream decodedInputStream = new GZIPInputStream(inputStream);
DataReader modelReader = new PlainTextFileDataReader(decodedInputStream);
MaxentModel loadedMaxentModel = new GISModelReader(modelReader).getModel();

// Now predicting the outcome using the loaded model
String[] context = {"a=1", "b=0"};
double[] outcomeProbs = loadedMaxentModel.eval(context);
String outcome = loadedMaxentModel.getBestOutcome(outcomeProbs);