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Natural Language Processing with Java
Natural Language Processing with Java

Natural Language Processing with Java: Explore various approaches to organize and extract useful text from unstructured data using Java

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Profile Icon Richard M Reese Profile Icon Richard M. Reese
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Full star icon Full star icon Full star icon Full star icon Half star icon 4.6 (7 Ratings)
Paperback Mar 2015 262 pages 1st Edition
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Arrow left icon
Profile Icon Richard M Reese Profile Icon Richard M. Reese
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Full star icon Full star icon Full star icon Full star icon Half star icon 4.6 (7 Ratings)
Paperback Mar 2015 262 pages 1st Edition
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Natural Language Processing with Java

Chapter 2. Finding Parts of Text

Finding parts of text is concerned with breaking text down into individual units called tokens, and optionally performing additional processing on these tokens. This additional processing can include stemming, lemmatization, stopword removal, synonym expansion, and converting text to lowercase.

We will demonstrate several tokenization techniques found in the standard Java distribution. These are included because sometimes this is all you may need to do the job. There may be no need to import NLP libraries in this situation. However, these techniques are limited. This is followed by a discussion of specific tokenizers or tokenization approaches supported by NLP APIs. These examples will provide a reference for how the tokenizers are used and the type of output they produce. This is followed by a simple comparison of the differences between the approaches.

There are many specialized tokenizers. For example, the Apache Lucene project supports tokenizers...

Understanding the parts of text

There are a number of ways of categorizing parts of text. For example, we may be concerned with character-level issues such as punctuations with a possible need to ignore or expand contractions. At the word level, we may need to perform different operations such as:

  • Identifying morphemes using stemming and/or lemmatization
  • Expanding abbreviations and acronyms
  • Isolating number units

We cannot always split words with punctuations because the punctuations are sometimes considered to be part of the word, such as the word "can't". We may also be concerned with grouping multiple words to form meaningful phrases. Sentence detection can also be a factor. We do not necessarily want to group words that cross sentence boundaries.

In this chapter, we are primarily concerned with the tokenization process and a few specialized techniques such as stemming. We will not attempt to show how they are used in other NLP tasks. Those efforts are reserved for later chapters...

What is tokenization?

Tokenization is the process of breaking text down into simpler units. For most text, we are concerned with isolating words. Tokens are split based on a set of delimiters. These delimiters are frequently whitespace characters. Whitespace in Java is defined by the Character class' isWhitespace method. These characters are listed in the following table. However, there may be a need at times to use a different set of delimiters. For example, different delimiters can be useful when whitespace delimiters obscure text breaks, such as paragraph boundaries, and detecting these text breaks is important.

Character

Meaning

Unicode space character

(space_separator, line_separator, or paragraph_separator)

\t

U+0009 horizontal tabulation

\n

U+000A line feed

\u000B

U+000B vertical tabulation

\f

U+000C form feed

\r

U+000D carriage return

\u001C

U+001C file separator

\u001D

U+001D group separator

\u001E

U+001E record separator

\u001F

U+001F...

Simple Java tokenizers

There are several Java classes that support simple tokenization; some of them are as follows:

  • Scanner
  • String
  • BreakIterator
  • StreamTokenizer
  • StringTokenizer

Although these classes provide limited support, it is useful to understand how they can be used. For some tasks, these classes will suffice. Why use a more difficult to understand and less efficient approach when a core Java class can do the job? We will cover each of these classes as they support the tokenization process.

The StreamTokenizer and StringTokenizer classes should not be used for new development. Instead, the String class' split method is usually a better choice. They have been included here in case you run across them and wonder whether they should be used or not.

Using the Scanner class

The Scanner class is used to read data from a text source. This might be standard input or it could be from a file. It provides a simple-to-use technique to support tokenization.

The Scanner class uses whitespace as the...

NLP tokenizer APIs

In this section, we will demonstrate several different tokenization techniques using the OpenNLP, Stanford, and LingPipe APIs. Although there are a number of other APIs available, we restricted the demonstration to these APIs. The examples will give you an idea of what techniques are available.

We will use a string called paragraph to illustrate these techniques. The string includes a new line break that may occur in real text in unexpected places. It is defined here:

private String paragraph = "Let's pause, \nand then ++ "reflect.";

Using the OpenNLPTokenizer class

OpenNLP possesses a Tokenizer interface that is implemented by three classes: SimpleTokenizer, TokenizerME, and WhitespaceTokenizer. This interface supports two methods:

  • tokenize: This is passed a string to tokenize and returns an array of tokens as strings.
  • tokenizePos: This is passed a string and returns an array of Span objects. The Span class is used to specify the beginning and ending offsets...

Understanding normalization

Normalization is a process that converts a list of words to a more uniform sequence. This is useful in preparing text for later processing. By transforming the words to a standard format, other operations are able to work with the data and will not have to deal with issues that might compromise the process. For example, converting all words to lowercase will simplify the searching process.

The normalization process can improve text matching. For example, there are several ways that the term "modem router" can be expressed, such as modem and router, modem & router, modem/router, and modem-router. By normalizing these words to the common form, it makes it easier to supply the right information to a shopper.

Understand that the normalization process might also compromise an NLP task. Converting to lowercase letters can decrease the reliability of searches when the case is important.

Normalization operations can include the following:

  • Changing characters...

Understanding the parts of text


There are a number of ways of categorizing parts of text. For example, we may be concerned with character-level issues such as punctuations with a possible need to ignore or expand contractions. At the word level, we may need to perform different operations such as:

  • Identifying morphemes using stemming and/or lemmatization

  • Expanding abbreviations and acronyms

  • Isolating number units

We cannot always split words with punctuations because the punctuations are sometimes considered to be part of the word, such as the word "can't". We may also be concerned with grouping multiple words to form meaningful phrases. Sentence detection can also be a factor. We do not necessarily want to group words that cross sentence boundaries.

In this chapter, we are primarily concerned with the tokenization process and a few specialized techniques such as stemming. We will not attempt to show how they are used in other NLP tasks. Those efforts are reserved for later chapters.

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Description

If you are a Java programmer who wants to learn about the fundamental tasks underlying natural language processing, this book is for you. You will be able to identify and use NLP tasks for many common problems, and integrate them in your applications to solve more difficult problems. Readers should be familiar/experienced with Java software development.

Who is this book for?

If you are a Java programmer who wants to learn about the fundamental tasks underlying natural language processing, this book is for you. You will be able to identify and use NLP tasks for many common problems, and integrate them in your applications to solve more difficult problems. Readers should be familiar/experienced with Java software development.

What you will learn

  • Develop a deep understanding of the basic NLP tasks and how they relate to each other
  • Discover and use the available tokenization engines
  • Implement techniques for end of sentence detection
  • Apply search techniques to find people and things within a document
  • Construct solutions to identify parts of speech within sentences
  • Use parsers to extract relationships between elements of a document
  • Integrate basic tasks to tackle more complex NLP problems

Product Details

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Publication date : Mar 27, 2015
Length: 262 pages
Edition : 1st
Language : English
ISBN-13 : 9781784391799
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Length: 262 pages
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ISBN-13 : 9781784391799
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Table of Contents

9 Chapters
1. Introduction to NLP Chevron down icon Chevron up icon
2. Finding Parts of Text Chevron down icon Chevron up icon
3. Finding Sentences Chevron down icon Chevron up icon
4. Finding People and Things Chevron down icon Chevron up icon
5. Detecting Part of Speech Chevron down icon Chevron up icon
6. Classifying Texts and Documents Chevron down icon Chevron up icon
7. Using Parser to Extract Relationships Chevron down icon Chevron up icon
8. Combined Approaches Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

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Ivan Zaitsev May 28, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Book about deep text processing using such tools as OpenNLP, LingPipe, Stanford NLP and other. From searching and tokenizing to classifying and extracting relationships. I usually use jdk standard instruments but these libraries are far more sophisticated and deserve attention.
Amazon Verified review Amazon
Amazon Customer May 31, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
It is a great book to start to learn programming NLP systems. I started with little experience with Java and NLPs in general but I did learn many things from this book: the basics of word and sentence tokenization, text classification and sentiment analysis, information extraction, parsing, meaning extraction, and question answering. This book will put would-be NLP programmers on their way to use the book’s code as the basis for their own software . Sometimes you won't get somethings when you first read but if you try the examples you will start to get what he is saying. One downside of the book is that some examples are focused on a single API( LingPipe, Apache OpenNLP or Stanford Parser) but I think they did that so you can think on your feet . From my point of view this book is worth every penny if you are programmer and you have to deal with software that needs to do some NLP.
Amazon Verified review Amazon
Danijel K. Nov 05, 2016
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Good book with a lot of concrete real code examples.
Amazon Verified review Amazon
Jon Borgman May 28, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Definitely a great resource for starting out with parsing text. The parts on tokenizers are very well done. Specifically the training of models and then using them was very helpful. What surprised me was the attention to the types of text parsed like what do you do when multiple acronyms and text speech are used. It does an amazing job at taking someone who is new to the subject and fills up your toolbox with tools and concepts that really give you a good picture or what / how to proceed.
Amazon Verified review Amazon
Stephen D. Williams May 27, 2015
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Provides a great introduction to NLP principles, problems, and related Java NLP libraries, with clear, concise example source code. This is a good way to get started with building NLP enabled applications using practical methods and clear code. To this, I would add example code coverage of the Mallet library, some summary of pros and cons of each library, mention of semantic web & graph databases with the presidents question answering example using DBPedia, and pointers to more expansive and ambitious examples.
Amazon Verified review Amazon
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