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Statistical parsing of English sentences

, 13 Dec 2006
Shows how to generate parse trees for English language sentences, using a C# port of OpenNLP, a statistical natural language parsing library.
englishparsing_bin.zip
Lithium.dll
ModelConverter.exe
OpenNLP Tools.chm
OpenNLP.dll
ParseTree.exe
SharpEntropy.dll
ToolsExample.exe
englishparsing_net2_0_bin.zip
ToolsExample.exe
Lithium.dll
ModelConverter.exe
OpenNLP Tools.chm
OpenNLP.dll
ParseTree.exe
SharpEntropy.dll
englishparsing_net2_0_src.zip
Lithium
Collections
Delegates
Enums
Interfaces
IO
Lithium.csproj.vspscc
LithiumControl.bmp
Shapes
UI
Visitors
ModelConverter
App.ico
ModelConverter.csproj.vspscc
ParseTree
App.ico
ParseTree.csproj.vspscc
ToolsExample
App.ico
ToolsExample.csproj.vspscc
OpenNLP
OpenNLP.csproj.vspscc
SharpEntropy.dll
Tools
Chunker
NameFind
Parser
PosTagger
SentenceDetect
Tokenize
Util
englishparsing_src.zip
Lithium.csproj.user
LithiumControl.bmp
App.ico
ModelConverter.csproj.user
OpenNLP.csproj.user
SharpEntropy.dll
vssver.scc
vssver.scc
vssver.scc
vssver.scc
vssver.scc
vssver.scc
vssver.scc
App.ico
ParseTree.csproj.user
App.ico
ToolsExample.csproj.user
//Copyright (C) 2005 Richard J. Northedge
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

//This file is based on the EnglishTreebankChunker.java source file found in the
//original java implementation of OpenNLP.  That source file contains the following header:

//Copyright (C) 2003 Thomas Morton
// 
//This library is free software; you can redistribute it and/or
//modify it under the terms of the GNU Lesser General Public
//License as published by the Free Software Foundation; either
//version 2.1 of the License, or (at your option) any later version.
// 
//This library is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU Lesser General Public License for more details.
// 
//You should have received a copy of the GNU Lesser General Public
//License along with this program; if not, write to the Free Software
//Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

using System;
using System.Collections;
using System.Text;

namespace OpenNLP.Tools.Chunker
{
	/// <summary>
	/// This is a chunker based on the CONLL chunking task which uses Penn Treebank constituents as the basis for the chunks.
	/// See   http://cnts.uia.ac.be/conll2000/chunking/ for data and task definition.
	/// </summary>
	/// <author> 
	/// Tom Morton
	/// </author>
	public class EnglishTreebankChunker : MaximumEntropyChunker
	{
		/// <summary>
		/// Creates an English Treebank Chunker which uses the specified model file.
		/// </summary>
		/// <param name="modelFile">
		/// The name of the maxent model to be used.
		/// </param>
		public EnglishTreebankChunker(string modelFile) : base(new SharpEntropy.GisModel(new SharpEntropy.IO.BinaryGisModelReader(modelFile)))
		{
		}
						
		/// <summary>
		/// This method determines whether the outcome is valid for the preceding sequence.  
		/// This can be used to implement constraints on what sequences are valid.  
		/// </summary>
		/// <param name="outcome">
		/// The outcome.
		/// </param>
		/// <param name="sequence">
		/// The preceding sequence of outcome assignments. 
		/// </param>
		/// <returns>
		/// true if the outcome is valid for the sequence, false otherwise.
		/// </returns>
		protected internal override bool ValidOutcome(string outcome, Util.Sequence sequence)
		{
			if (outcome.StartsWith("I-"))
			{
				ArrayList tagList = sequence.Outcomes;
				int lastTagIndex = tagList.Count - 1;
				if (lastTagIndex == - 1)
				{
					return (false);
				}
				else
				{
					string lastTag = (string) tagList[lastTagIndex];
					if (lastTag == "O")
					{
						return false;
					}
					if (lastTag.Substring(2) != outcome.Substring(2))
					{
						return false;
					}
				}
			}
			return true;
		}
		
		/// <summary>
		/// Gets formatted chunk information for a specified sentence.
		/// </summary>
		/// <param name="tokens">
		/// string array of tokens in the sentence
		/// </param>
		/// <param name="tags">
		/// string array of POS tags for the tokens in the sentence
		/// </param>
		/// <returns>
		/// A string containing the formatted chunked sentence
		/// </returns>
		public string GetChunks(string[] tokens, string[] tags)
		{
			StringBuilder output = new StringBuilder();

			string[] chunks = Chunk(tokens, tags);
			for (int currentChunk = 0, chunkCount = chunks.Length; currentChunk < chunkCount; currentChunk++)
			{
				if (currentChunk > 0 && !chunks[currentChunk].StartsWith("I-") && chunks[currentChunk - 1] != "O")
				{
					output.Append(" ]");
				}
				if (chunks[currentChunk].StartsWith("B-"))
				{
					output.Append(" [" + chunks[currentChunk].Substring(2));
				}
				
				output.Append(" " + tokens[currentChunk] + "/" + tags[currentChunk]);
			}
			if (chunks[chunks.Length - 1] != "O")
			{
				output.Append(" ]");
			}
			output.Append("\r\n");

			return output.ToString();

		}

		/// <summary>
		/// Gets formatted chunk information for a specified sentence.
		/// </summary>
		/// <param name="data">
		/// a string containing a list of tokens and tags, separated by / characters. For example:
		/// Battle-tested/JJ Japanese/NNP industrial/JJ managers/NNS 
		/// </param>
		/// <returns>
		/// A string containing the formatted chunked sentence
		/// </returns>
		public string GetChunks(string data)
		{
			StringBuilder output = new StringBuilder();
			string[] tokenAndTags = data.Split(' ');
			string[] tokens = new string[tokenAndTags.Length];
			string[] tags = new string[tokenAndTags.Length];
			for (int currentTokenAndTag = 0, tokenAndTagCount = tokenAndTags.Length; currentTokenAndTag < tokenAndTagCount; currentTokenAndTag++)
			{
				string[] tokenAndTag = tokenAndTags[currentTokenAndTag].Split('/');
				tokens[currentTokenAndTag] = tokenAndTag[0];
				tags[currentTokenAndTag] = tokenAndTag[1];
			}

			return GetChunks(tokens, tags);
		}
	}
}

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About the Author

Richard Northedge
Web Developer
United Kingdom United Kingdom
Richard Northedge is a senior developer with a UK Microsoft Gold Partner company. He has a postgraduate degree in English Literature, has been programming professionally since 1998 and has been an MCSD since 2000.

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