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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
englishparsing_net2_0_bin.zip
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 BuildContextGenerator.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.Generic;
using System.Text;

namespace OpenNLP.Tools.Parser
{
	/// <summary>
	/// Class to generator predictive contexts for deciding how constituents should be combined together.
	/// </summary>
	public class BuildContextGenerator : SharpEntropy.IContextGenerator
	{
		
		private const string mEndOfSentence = "eos";
		
		/// <summary> 
		/// Creates a new context generator for making decisions about combining constituents together.
		/// </summary>
		public BuildContextGenerator()
		{
		}

        /// <summary>
        /// Returns the predictive context used to determine how the constituent at the specified index 
        /// should be combined with other constituents. 
        /// </summary>
        /// <param name="input">
        /// Object array containing an array of Parse objects (the uncombined constituents), and the index of the
        /// relevant constituent.
        /// </param>
		public virtual string[] GetContext(object input)
		{
			object[] parameters = (object[]) input;
			return GetContext((Parse[]) parameters[0], ((int) parameters[1]));
		}
		
		private string MakeConstituent(Parse inputParse, int index)
		{
			StringBuilder feature = new StringBuilder(20);
			feature.Append(index).Append("=");
			if (inputParse != null)
			{
				if (index < 0)
				{
					feature.Append(inputParse.Label).Append("|");
				}
				feature.Append(inputParse.Type).Append("|").Append(inputParse.Head.ToString());
			}
			else
			{
				feature.Append(mEndOfSentence).Append("|").Append(mEndOfSentence).Append("|").Append(mEndOfSentence);
			}
			return feature.ToString();
		}
		
		private string MakeConstituentBackOff(Parse inputParse, int index)
		{
			StringBuilder feature = new StringBuilder(20);
			feature.Append(index).Append("*=");
			if (inputParse != null)
			{
				if (index < 0)
				{
					feature.Append(inputParse.Label).Append("|");
				}
				feature.Append(inputParse.Type);
			}
			else
			{
				feature.Append(mEndOfSentence).Append("|").Append(mEndOfSentence);
			}
			return feature.ToString();
		}
		
		/// <summary>
		/// Returns the predictive context used to determine how the constituent at the specified index 
        /// should be combined with other constituents. 
		/// </summary>
		/// <param name="constituents">
		/// The constituents which have yet to be combined into new constituents.
		/// </param>
		/// <param name="index">
		/// The index of the constituent whcihi is being considered.
		/// </param>
		/// <returns>
		/// the context for building constituents at the specified index.
		/// </returns>
		public virtual string[] GetContext(Parse[] constituents, int index)
		{
			List<string> features = new List<string>(100);
			int constituentCount = constituents.Length;
			
			//default 
			features.Add("default");
			// cons(-2), cons(-1), cons(0), cons(1), cons(2)
			// cons(-2)
			Parse previousPreviousParse = null;
			Parse previousParse = null;
			Parse currentParse = null;
			Parse nextParse = null;
			Parse nextNextParse = null;
			
			if (index - 2 >= 0)
			{
				previousPreviousParse = constituents[index - 2];
			}
			if (index - 1 >= 0)
			{
				previousParse = constituents[index - 1];
			}
			currentParse = constituents[index];
			if (index + 1 < constituentCount)
			{
				nextParse = constituents[index + 1];
			}
			if (index + 2 < constituentCount)
			{
				nextNextParse = constituents[index + 2];
			}
			
			// cons(-2), cons(-1), cons(0), cons(1), cons(2)
			string previousPreviousConstituent = MakeConstituent(previousPreviousParse, - 2);
			string previousConstituent = MakeConstituent(previousParse, - 1);
			string currentConstituent = MakeConstituent(currentParse, 0);
			string nextConstituent = MakeConstituent(nextParse, 1);
			string nextNextConstituent = MakeConstituent(nextNextParse, 2);
			
			string previousPreviousConstituentBackOff = MakeConstituentBackOff(previousPreviousParse, - 2);
			string previousConstituentBackOff = MakeConstituentBackOff(previousParse, - 1);
			string currentConstituentBackOff = MakeConstituentBackOff(currentParse, 0);
			string nextConstituentBackOff = MakeConstituentBackOff(nextParse, 1);
			string nextNextConstituentBackOff = MakeConstituentBackOff(nextNextParse, 2);
			
			// cons(-2), cons(-1), cons(0), cons(1), cons(2)
			features.Add(previousPreviousConstituent);
			features.Add(previousPreviousConstituentBackOff);
			features.Add(previousConstituent);
			features.Add(previousConstituentBackOff);
			features.Add(currentConstituent);
			features.Add(currentConstituentBackOff);
			features.Add(nextConstituent);
			features.Add(nextConstituentBackOff);
			features.Add(nextNextConstituent);
			features.Add(nextNextConstituentBackOff);
			
			// cons(-1,0), cons(0,1)
			features.Add(previousConstituent + "," + currentConstituent);
			features.Add(previousConstituentBackOff + "," + currentConstituent);
			features.Add(previousConstituent + "," + currentConstituentBackOff);
			features.Add(previousConstituentBackOff + "," + currentConstituentBackOff);
			
			features.Add(currentConstituent + "," + nextConstituent);
			features.Add(currentConstituentBackOff + "," + nextConstituent);
			features.Add(currentConstituent + "," + nextConstituentBackOff);
			features.Add(currentConstituentBackOff + "," + nextConstituentBackOff);
			
			// cons3(-2,-1,0), cons3(-1,0,1), cons3(0,1,2)
			features.Add(previousPreviousConstituent + "," + previousConstituent + "," + currentConstituent);
			features.Add(previousPreviousConstituentBackOff + "," + previousConstituent + "," + currentConstituent);
			features.Add(previousPreviousConstituent + "," + previousConstituentBackOff + "," + currentConstituent);
			features.Add(previousPreviousConstituentBackOff + "," + previousConstituentBackOff + "," + currentConstituent);
			features.Add(previousPreviousConstituentBackOff + "," + previousConstituentBackOff + "," + currentConstituentBackOff);
			
			features.Add(previousConstituent + "," + currentConstituent + "," + nextConstituent);
			features.Add(previousConstituentBackOff + "," + currentConstituent + "," + nextConstituent);
			features.Add(previousConstituent + "," + currentConstituent + "," + nextConstituentBackOff);
			features.Add(previousConstituentBackOff + "," + currentConstituent + "," + nextConstituentBackOff);
			features.Add(previousConstituentBackOff + "," + currentConstituentBackOff + "," + nextConstituentBackOff);
			
			features.Add(currentConstituent + "," + nextConstituent + "," + nextNextConstituent);
			features.Add(currentConstituent + "," + nextConstituentBackOff + "," + nextNextConstituent);
			features.Add(currentConstituent + "," + nextConstituent + "," + nextNextConstituentBackOff);
			features.Add(currentConstituent + "," + nextConstituentBackOff + "," + nextNextConstituentBackOff);
			features.Add(currentConstituentBackOff + "," + nextConstituentBackOff + "," + nextNextConstituentBackOff);
			
			// punct
			string currentParseWord = currentParse.ToString();
			if (currentParseWord == "-RRB-")
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.ToString() == "-LRB-")
					{
						features.Add("bracketsmatch");
						break;
					}
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						break;
					}
				}
			}
			if (currentParseWord == "-RCB-")
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.ToString() == "-LCB-")
					{
						features.Add("bracketsmatch");
						break;
					}
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						break;
					}
				}
			}
			if (currentParseWord == "''")
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.ToString() == "``")
					{
						features.Add("quotesmatch");
						break;
					}
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						break;
					}
				}
			}
			if (currentParseWord == "'")
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.ToString() == "`")
					{
						features.Add("quotesmatch");
						break;
					}
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						break;
					}
				}
			}
			if (currentParseWord == ",")
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.ToString() == ",")
					{
						features.Add("iscomma");
						break;
					}
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						break;
					}
				}
			}
			if (currentParseWord == (".") && index == constituentCount - 1)
			{
				for (int parseIndex = index - 1; parseIndex >= 0; parseIndex--)
				{
					Parse testParse = constituents[parseIndex];
					if (testParse.Label.StartsWith(MaximumEntropyParser.StartPrefix))
					{
						if (parseIndex == 0)
						{
							features.Add("endofsentence");
						}
						break;
					}
				}
			}
			return features.ToArray();
		}
	}
}

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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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