Text normalization techniques based on rules, lexicons or supervised training requiring large corpora are not scalable nor domain interchangeable, and this makes them unsuitable for normalizing user-generated content (UGC). Current tools available for Brazilian Portuguese make use of such techniques. In this work we propose a technique based on distributed representation of words (or word embeddings). It generates continuous numeric vectors of high-dimensionality to represent words. The vectors explicitly encode many linguistic regularities and patterns, as well as syntactic and semantic word relationships. Words that share semantic similarity are represented by similar vectors. Based on these features, we present a totally unsupervised, expandable and language and domain independent method for learning normalization lexicons from word embeddings. Our approach obtains high correction rate of orthographic errors and internet slang in product reviews, outperforming the current available tools for Brazilian Portuguese.
@cite_13: User-generated contents (UGC) represent an important source of information for governments, companies, political candidates and consumers. However, most of the Natural Language Processing tools and techniques are developed from and for texts of standard language, and UGC is a type of text especially full of creativity and idiosyncrasies, which represents noise for NLP purposes. This paper presents UGCNormal, a lexicon-based tool for UGC normalization. It encompasses a tokenizer, a sentence segmentation tool, a phonetic-based speller and some lexicons, which were originated from a deep analysis of a corpus of product reviews in Brazilian Portuguese. The normalizer was evaluated in two different data sets and carried out from 31 to 89 of the appropriate corrections, depending on the type of text noise. The use of UGCNormal was also validated in a task of POS tagging, which improved from 91.35 to 93.15 in accuracy and in a task of opinion classification, which improved the average of F1-score measures (F1-score positive and F1-score negative) from 0.736 to 0.758.
Since a large part of misspellings found in UGC is phonetically-motivated, @cite_13 proposed a phonetic-based speller for correcting such errors. The speller combines edit distance and several specific phonetic rules for Portuguese in order to generate correction candidates. The correction of internet slang and proper name and acronyms capitalization is based on a set of lexicons. Each lexicon contains many pairs of wrong--correct form of words. The correction is performed by looking up the noisy word in the lexicon and substituting it by the correct version. Despite this technique achieving good results in the product review domain, it is not scalable and is too restricted, since there is no form of automatic lexicon-learning. Therefore, it is not suitable for a generic, domain-free normalizer. The results obtained by @cite_13 will be further discussed, as they are the main source of comparison for our work.