Words Are Important

Lexicon-based sentiment analysis (SA) aims to address the problem of extracting people’s opinions from their comments on the Web using a predefined lexicon of opinionated words. In contrast to the machine learning (ML) approach, lexicon-based methods are domain-independent methods that do not need a large annotated training corpus and hence are faster. This makes the lexicon-based approach prevalent in the SA community. However, the story is different for the Persian language. In contrast to English, using the lexicon-based method in Persian is a new discipline. There are rather limited resources available for SA in Persian, making the accuracy of the existing lexicon-based methods lower than other languages. In the current study, first an exhaustive investigation of the lexicon-based method is performed. Then two new resources are introduced to address the problem of resource scarcity for SA in Persian: a carefully labeled lexicon of sentiment words, PerLex, and a new handmade dataset of about 16,000 rated documents, PerView. Moreover, a new hybrid method using both ML and the lexicon-based approach is presented in which PerLex words are used to train the ML algorithm. Experiments are carried out on our new PerView dataset. Results indicate that the accuracy of PerLex is higher than the existing CNRC, Adjectives, SentiStrength, PerSent, and LexiPers lexicons. In addition, the results show that using PerLex significantly decreases the execution time of the proposed system in comparison to the above-mentioned lexicons. Moreover, the results demonstrate the excellence of using opinionated lexicon terms followed by bigrams as the features employed in the ML method.