Sentiment Analysis and Opinion Mining by Bing Liu

Author:Bing Liu [Liu, Bing]
Language: eng
Format: epub
Publisher: Morgan & Claypool Publishers
Published: 2012-05-22T16:31:59+00:00

CHAPTER 6

Sentiment Lexicon Generation

By now, it should be quite clear that words and phrases that convey positive or negative sentiments are instrumental for sentiment analysis. This chapter discusses how to compile such words lists. In the research literature, sentiment words are also called opinion words, polar words, or opinion-bearing words. Positive sentiment words are used to express some desired states or qualities while negative sentiment words are used to express some undesired states or qualities. Examples of positive sentiment words are beautiful, wonderful, and amazing. Examples of negative sentiment words are bad, awful, and poor. Apart from individual words, there are also sentiment phrases and idioms, e.g., cost someone an arm and a leg. Collectively, they are called sentiment lexicon (or opinion lexicon). For easy presentation, from now on when we say sentiment words, we mean both individual words and phrases.

Sentiment words can be divided into two types: base type and comparative type. All the example words above are of the base type. Sentiment words of the comparative type (which include the superlative type) are used to express comparative and superlative opinions. Examples of such words are better, worse, best, worst, etc., which are comparative and superlative forms of their base adjectives or adverbs, e.g., good and bad. Unlike sentiment words of the base type, sentiment words of the comparative type do not express a regular opinion on an entity but a comparative opinion on more than one entity, e.g., “Pepsi tastes better than Coke.” This sentence does not express an opinion saying that any of the two drinks is good or bad. It just says that compared to Coke, Pepsi tastes better. We will discuss comparative and superlative sentiment words further in Chapter 8. This chapter focuses only on sentiment words of the base type.

Researchers have proposed many approaches to compile sentiment words. Three main approaches are: manual approach, dictionary-based approach, and corpus-based approach. The manual approach is labor intensive and time consuming, and is thus not usually used alone but combined with automated approaches as the final check, because automated methods make mistakes. Below, we discuss the two automated approaches. Along with them, we will also discuss the issue of factual statements implying opinions, which has largely been overlooked by the research community.

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