With a growing amount of subjective content distributed across the Web, there is a need for a domain-independent information retrieval system that would support ad hoc retrieval of documents expressing opinions on a specific topic of the user’s query. While the research area of opinion detection and sentiment analysis has received much attention in the recent years, little research has been done on identifying subjective content targeted at a specific topic, i.e. expressing topical opinion. This thesis presents a novel method for ad hoc retrieval of documents which contain subjective content on the topic of the query. Documents are ranked by the likelihood each document expresses an opinion on a query term, approximated as the likelihood any occurrence of the query term is modified by a subjective adjective. Domain-independent user-based evaluation of the proposed methods was conducted, and shows statistically significant gains over Google ranking as the baseline.

Sentiment analysis is the automatic classification of a text, trying to determine the attitude of the writer with respect to a specific topic. The attitude may be either their judgment or evaluation, their feelings or the intended emotional communication. The recent increase in the use of review sites and blogs, has made a great amount of subjective data available. Nowadays, it is nearly impossible to manually process all the relevant data available, and as a consequence, the importance given to the automatic classification of unformatted data, has increased. Up to date, all of the research carried on sentiment analysis was focused on English language. In this thesis, two Turkish datasets tagged with sentiment information is introduced and existing methods for English are applied on these datasets. This thesis also suggests new methods for Turkish sentiment analysis.

Pastaruosius keletą metų, žmonėms vis aktyviau pradėjus reikšti savo požiūrį, įsitikinimus ir potyrius internete, susiformavo nauja tyrinėjimų sritis, kuri apima nuomonių gavybą ir sentimentų analizę. Šios srities tyrinėjimus aktyviai skatina ir jais domisi įvairios verslo kompanijos, matančios didelį, dėka nuolat tobulėjančių rezultatų, praktinį potencialą. Šis darbas skirtas apžvelgti teorinius bei praktinius nuomonės gavybos ir sentimentų analizės rezultatus bei realizuoti prototipinę nuomonės analizės sistemą, skirtą tyrinėti trumpus komentarus, parašytus lietuvių kalba. Taip pat darbe aprašomos problemos, susijusios su lietuvių kalbos taikymu nuomonės gavybos ir sentimentų analizės sistemų veikloje. Galiausiai, baigiamojoje dalyje suformuluojami ir išdėstomi rekomendacinio pobūdžio etapai, skirti nuomonės analizės sistemų kūrimui bei tobulinimui. / In past few years, more and more people started to express their views, beliefs and experiences on the Internet. This caused the emergence of a new research field, which includes opinion mining and sentiment analysis. Various business companies are actively interested in researches of this domain and seeing big potential for practical adaptation of the results. This Master Thesis covers the review of theoretical and practical results of opinion mining and sentiment analysis, including attempt of creating prototype system for opinion analysis of comments in Lithuanian. Also this study aims to identify problems related to adaptation of Lithuanian language in opinion mining and sentiment analysis system work. Finally, last part contains of the formulated guidance steps for development and improvement of the opinion mining and sentiment analysis.

Vis aktyviau pasaulyje yra domimasi sentimentų analize. Verslininkai, garsių pasaulyje įmonių atstovai naudojasi sentimentų analizės įrankiais, kurie leidžia analizuoti tūkstančius vartotojų komentarų (Twitter, Facebook socialiniuose tinkluose, kituose tinklalapiuose). Išanalizavus internetinius komentarus suinteresuotos šalys mato kaip vertinami jų produktai ar paslaugos, prekės ženklai, darbuotojai. Tai naudinga informacija, kuri padeda valdyti savo verslą. Deja, tokių įrankių skirtų lietuvių kalbai nėra. Šio darbo tikslas išanalizavus nuomonių gavybos metodus parengti sprendimą tinkamą lietuviškų internetinių tekstų sentimentų analizei ir jį įgyvendinti. Šiame darbe yra analizuojami sentimentų analizės metodai, egzistuojantys sentimentų analizės įrankiai. Taip pat pateikiamas metodikos lietuviškų tekstų nuomonių analizei formulavimas, pagrindžiant bandymais. Darbo eigoje sukurtas įrankių rinkinys Python kalba, leidžiantis išbandyti siūlomą metodiką. Darbas užbaigiamas rekomendacijomis, kurios leistų patobulinti sukurtą įrankių rinkinį. / Interest in the analysis of sentiment in the world is rising. Entrepreneurs, representatives from world famous companies are using analysis tools ofsentiments that allow to analyze thousands of users comments (Twitter, Facebook,in social networks, or other sites). After analysis of online comments interested parties can see how is valued their products or services, brands, and employees. This is a useful information, that helps you to manage your business. Unfortunately, there is no such tools for the Lithuanian language. The aim of this analysis is to develop and implement methods for extracting the proper sentiments of decision in Lithuanian texts online. In this paper is an overview of analytical methods, existing sentiment analysis tools. It is also provided formulation of a methodology of Lithuanian texts opinion for its analysis, based on justification tests. During a work process was created a set of tools developed in Python that allows to test the proposed methodology. Work is completed with recomendations, which allows to improve the developed Toolkit.

Genre and domain influence an author\'s style of writing and therefore a text\'s characteristics. Natural language processing is prone to such variations in textual characteristics: it is said to be genre and domain dependent. This thesis investigates genre and domain dependencies in sentiment analysis. Its goal is to support the development of robust sentiment analysis approaches that work well and in a predictable manner under different conditions, i.e. for different genres and domains. Initially, we show that a prototypical approach to sentiment analysis -- viz. a supervised machine learning model based on word n-gram features -- performs differently on gold standards that originate from differing genres and domains, but performs similarly on gold standards that originate from resembling genres and domains. We show that these gold standards differ in certain textual characteristics, viz. their domain complexity. We find a strong linear relation between our approach\'s accuracy on a particular gold standard and its domain complexity, which we then use to estimate our approach\'s accuracy. Subsequently, we use certain textual characteristics -- viz. domain complexity, domain similarity, and readability -- in a variety of applications. Domain complexity and domain similarity measures are used to determine parameter settings in two tasks. Domain complexity guides us in model selection for in-domain polarity classification, viz. in decisions regarding word n-gram model order and word n-gram feature selection. Domain complexity and domain similarity guide us in domain adaptation. We propose a novel domain adaptation scheme and apply it to cross-domain polarity classification in semi- and unsupervised domain adaptation scenarios. Readability is used for feature engineering. We propose to adopt readability gradings, readability indicators as well as word and syntax distributions as features for subjectivity classification. Moreover, we generalize a framework for modeling and representing negation in machine learning-based sentiment analysis. This framework is applied to in-domain and cross-domain polarity classification. We investigate the relation between implicit and explicit negation modeling, the influence of negation scope detection methods, and the efficiency of the framework in different domains. Finally, we carry out a case study in which we transfer the core methods of our thesis -- viz. domain complexity-based accuracy estimation, domain complexity-based model selection, and negation modeling -- to a gold standard that originates from a genre and domain hitherto not used in this thesis.

Sentiment analysis is a challenging task today for computational linguistics. Because of the rise of the social Web, both the research and the industry are interested in automatic processing of opinions in text. In this work, we assume a multilingual and multidomain environment and aim at automatic and adaptive polarity classification.We propose a method for automatic construction of multilingual affective lexicons from microblogging to cover the lack of lexical resources. To test our method, we have collected over 2 million messages from Twitter, the largest microblogging platform, and have constructed affective resources in English, French, Spanish, and Chinese.We propose a text representation model based on dependency parse trees to replace a traditional n-grams model. In our model, we use dependency triples to form n-gram like features. We believe this representation covers the loss of information when assuming independence of words in the bag-of-words approach.Finally, we investigate the impact of entity-specific features on classification of minor opinions and propose normalization schemes for improving polarity classification. The proposed normalization schemes gives more weight to terms expressing sentiments and lower the importance of noisy features.The effectiveness of our approach has been proved in experimental evaluations that we have performed across multiple domains (movies, product reviews, news, blog posts) and multiple languages (English, French, Russian, Spanish, Chinese) including official participation in several international evaluation campaigns (SemEval'10, ROMIP'11, I2B2'11).

A análise de contradições é uma área relativamente nova, multidisciplinar e complexa que tem por objetivo principal identificar pedaços contraditórios de texto. Ela pode ser abordada a partir das perspectivas de diferentes áreas de pesquisa, tais como processamento de linguagem natural, mineração de opinioes, recuperação de informações e extração de Informações. Este trabalho foca no problema de detectar contradições em textos – mais especificamente, nas contradições que são o resultado da diversidade de sentimentos entre as sentenças de um determinado texto. Ao contrário de outros tipos de contradições, a detecção de contradições baseada em sentimentos pode ser abordada como uma etapa de pós-processamento na tarefa tradicional de análise de sentimentos. Neste contexto, este trabalho apresenta duas contribuições principais. A primeira é um estudo exploratório da tarefa de classificação, na qual identificamos e usamos diferentes ferramentas e recursos. A segunda contribuição é a adaptação e a extensão de um framework de análise contradição existente, filtrando seus resultados para remover os comentários erroneamente rotulados como contraditórios. O método de filtragem baseia-se em dois algoritmos simples de similaridade entre palavras. Uma avaliação experimental em comentários sobre produtos reais mostrou melhorias proporcionais de até 30 % na acurácia da classificação e 26 % na precisão da detecção de contradições. / Contradiction Analysis is a relatively new multidisciplinary and complex area with the main goal of identifying contradictory pieces of text. It can be addressed from the perspectives of different research areas such as Natural Language Processing, Opinion Mining, Information Retrieval, and Information Extraction. This work focuses on the problem of detecting sentiment-based contradictions which occur in the sentences of a given review text. Unlike other types of contradictions, the detection of sentiment-based contradictions can be tackled as a post-processing step in the traditional sentiment analysis task. In this context, we make two main contributions. The first is an exploratory study of the classification task, in which we identify and use different tools and resources. Our second contribution is adapting and extending an existing contradiction analysis framework by filtering its results to remove the reviews that are erroneously labeled as contradictory. The filtering method is based on two simple term similarity algorithms. An experimental evaluation on real product reviews has shown proportional improvements of up to 30% in classification accuracy and 26% in the precision of contradiction detection.

Na WEB, são encontradas postagens sobre assuntos variados, notícias de celebridades, produtos e serviços. Tal conteúdo contém emoções positivas, negativas ou neutras. Minerar o sentimento da população sobre candidatos a eleições e seus aspectos em mídias virtuais pode ser realizado por meio de técnicas de Mineração de Opiniões. Existem soluções para fontes de opinião fortemente estruturadas, tais como revisões de produtos e serviços, no entanto o problema que se apresenta é realizar a mineração de opiniões em nível de aspecto em fontes de opiniões fracamente estruturadas. Além de avaliar conceitos relacionados à mineração de opiniões, o presente trabalho descreve a realização de um estudo de caso, o qual analisa fontes de opiniões fracamente estruturadas e propõe uma abordagem para minerar opiniões em nível de aspecto, utilizando como fontes de opinião comentários de leitores de jornais. O estudo de caso contribui (i) na concepção de uma abordagem para identificação da opinião em nível de aspecto sobre entidades eleitorais em comentários de notícias políticas, (ii) na aplicação de um método baseado em aprendizagem de máquina para classificar a opinião sobre entidades e seus aspectos em três classes (positivo, negativo e neutro), (iii) na representação da sumarização visual de opinião sobre entidades e seus aspectos. São descritos experimentos para identificar comentários que mencionam os aspectos saúde e educação, utilizando co-ocorrência, em que foram obtidos resultados satisfatórios utilizando as técnicas Expected Mutual Information Measure e phi-squared. Já para a polarização de sentenças, são realizados experimentos com duas abordagens de classificação: uma que classifica sentenças em três classes e outra que realiza classificações binárias em duas etapas. / In the WEB are found posts about various subjects like celebrity news, products and services. Such content has positive, negative or neutral emotions. Mining the population’s sentiments about elections candidates and their aspects in virtual media can be performed using Opinion Mining techniques. There are solutions for highly structured opinion sources, such as reviews of products and services, however the problem is how to perform aspect-based opinion mining in less structured opinions sources. Besides evaluating concepts related to opinion mining, this work describes a case study which analyzes weakly structured sources and proposes an approach to mine aspect-based opinions using as sources of sentiment reviews of newspaper readers. The case study contributes (i) designing an approach to identify the aspect-based opinion about electoral candidates in news political comments, (ii) to the application of a machine learning-based method to classify the opinion about entities and their aspects in three classes (positive, negative and neutral) (iii) to the representation of a visual summarization review of entities and their aspects. It describes experiments to identify comments about health and education aspects using co-occurrence where satisfactory results were obtained using the techniques Expected Mutual Information Measure and phi-squared. In which regards sentences polarization, experiments are performed with two classification approaches, one that classifies sentences in three classes and another that performs binary classifications in two stages.

Com a crescente expansão da Web, cada vez mais usuários compartilham suas opiniões sobre experiências vividas. Essas opiniões estão, na maioria das vezes, representadas sob a forma de texto não estruturado. A Análise de Sentimentos (ou Mineração de Opinião) é a área dedicada ao estudo computacional das opiniões e sentimentos expressos em textos, tipicamente classificando-os de acordo com a sua polaridade (i.e., como positivos ou negativos). Ao mesmo tempo em que sites de vendas e redes sociais tornam-se grandes fontes de opiniões, cresce a busca por ferramentas que, de forma automática, classifiquem as opiniões e identifiquem a qual aspecto da entidade avaliada elas se referem. Neste trabalho, propomos métodos direcionados a dois pontos fundamentais para o tratamento dessas opiniões: (i) análise de sentimentos baseada em aspectos e (ii) atribuição de polaridade. Para a análise de sentimentos baseada em aspectos, desenvolvemos um método que identifica expressões que mencionem aspectos e entidades em um texto, utilizando ferramentas de processamento de linguagem natural combinadas com algoritmos de aprendizagem de máquina. Para a atribuição de polaridade, desenvolvemos um método que utiliza 24 atributos extraídos a partir do ranking gerado por um motor de busca e para gerar modelos de aprendizagem de máquina. Além disso, o método não depende de recursos linguísticos e pode ser aplicado sobre dados com ruídos. Experimentos realizados sobre datasets reais demonstram que, em ambas as contribuições, conseguimos resultados próximos aos dos baselines mesmo com um número pequeno de atributos. Ainda, para a atribuição de polaridade, os resultados são comparáveis aos de métodos do estado da arte que utilizam técnicas mais complexas. / With the growing expansion of the Web, more and more users share their views on experiences they have had. These views are, in most cases, represented in the form of unstructured text. The Sentiment Analysis (or Opinion Mining) is a research area dedicated to the computational study of the opinions and feelings expressed in texts, typically categorizing them according to their polarity (i.e., as positive or negative). As on-line sales and social networking sites become great sources of opinions, there is a growing need for tools that classify opinions and identify to which aspect of the evaluated entity they refer to. In this work, we propose methods aimed at two key points for the treatment of such opinions: (i) aspect-based sentiment analysis and (ii) polarity assignment. For aspect-based sentiment analysis, we developed a method that identifies expressions mentioning aspects and entities in text, using natural language processing tools combined with machine learning algorithms. For the identification of polarity, we developed a method that uses 24 attributes extracted from the ranking generated by a search engine to generate machine learning models. Furthermore, the method does not rely on linguistic resources and can be applied to noisy data. Experiments on real datasets show that, in both contributions, our results using a small number of attributes were similar to the baselines. Still, for assigning polarity, the results are comparable to prior art methods that use more complex techniques.

Emotions and sentiments play a crucial role in our everyday lives. They aid decision-making, learning, communication, and situation awareness in human-centric environments. Over the past two decades, researchers in artificial intelligence have been attempting to endow machines with cognitive capabilities to recognize, infer, interpret and express emotions and sentiments. All such efforts can be attributed to affective computing, an interdisciplinary field spanning computer science, psychology, social sciences and cognitive science. Sentiment analysis and emotion recognition has also become a new trend in social media, avidly helping users understand opinions being expressed on different platforms in the web. In this thesis, we focus on developing novel methods for text-based sentiment analysis. As an application of the developed methods, we employ them to improve multimodal polarity detection and emotion recognition. Specifically, we develop innovative text and visual-based sentiment-analysis engines and use them to improve the performance of multimodal sentiment analysis. We begin by discussing challenges involved in both text-based and multimodal sentiment analysis. Next, we present a number of novel techniques to address these challenges. In particular, in the context of concept-based sentiment analysis, a paradigm gaining increasing interest recently, it is important to identify concepts in text; accordingly, we design a syntaxbased concept-extraction engine. We then exploit the extracted concepts to develop conceptbased affective vector space which we term, EmoSenticSpace. We then use this for deep learning-based sentiment analysis, in combination with our novel linguistic pattern-based affective reasoning method termed sentiment flow. Finally, we integrate all our text-based techniques and combine them with a novel deep learning-based visual feature extractor for multimodal sentiment analysis and emotion recognition. Comparative experimental results using a range of benchmark datasets have demonstrated the effectiveness of the proposed approach.