title: An investigation into the use of negation in Inductive Rule Learning for text classification
Creators: name: Chua, Stephanie Hui Li
Publisher: name: University of Liverpool Repository
Year: 2013

description: This thesis seeks to establish if the use of negation in Inductive Rule Learning (IRL) for text classification is effective. Text classification is a widely research topic in the domain of data mining. There have been many techniques directed at text classification; one of them is IRL, widely chosen because of its simplicity, comprehensibility and interpretability by humans. IRL is a process whereby rules in the form of $antecedent -&gt; conclusion$ are learnt to build a classifier. Thus, the learnt classifier comprises a set of rules, which are used to perform classification. To learn a rule, words from pre-labelled documents, known as features, are selected to be used as conjunctions in the rule antecedent. These rules typically do not include any negated features in their antecedent; although in some cases, as demonstrated in this thesis, the inclusion of negation is required and beneficial for the text classification task. With respect to the use of negation in IRL, two issues need to be addressed: (i) the identification of the features to be negated and (ii) the improvisation of rule refinement strategies to generate rules both with and without negation. To address the first issue, feature space division is proposed, whereby the feature space containing features to be used for rule refinement is divided into three sub-spaces to facilitate the identification of the features which can be advantageously negated. To address the second issue, eight rule refinement strategies are proposed, which are able to generate both rules with and without negation. Typically, single keywords which are deemed significant to differentiate between classes are selected to be used in the text representation in the text classification task. Phrases have also been proposed because they are considered to be semantically richer than single keywords. Therefore, with respect to the work conducted in this thesis, three different types of phrases ($n$-gram phrases, keyphrases and fuzzy phrases) are extracted to be used as the text representation in addition to the use of single keywords. To establish the effectiveness of the use of negation in IRL, the eight proposed rule refinement strategies are compared with one another, using keywords and the three different types of phrases as the text representation, to determine whether the best strategy is one which generates rules with negation or without negation. Two types of classification tasks are conducted; binary classification and multi-class classification. The best strategy in the proposed IRL mechanism is compared to five existing text classification techniques with respect to binary classification: (i) the Sequential Minimal Optimization (SMO) algorithm, (ii) Naive Bayes (NB), (iii) JRip, (iv) OlexGreedy and (v) OlexGA from the Waikato Environment for Knowledge Analysis (WEKA) machine learning workbench. In the multi-class classification task, the proposed IRL mechanism is compared to the Total From Partial Classification (TFPC) algorithm. The datasets used in the experiments include three text datasets: 20 Newsgroups, Reuters-21578 and Small Animal Veterinary Surveillance Network (SAVSNET) datasets and five UCI Machine Learning Repository tabular datasets. The results obtained from the experiments showed that the strategies which generated rules with negation were more effective when the keyword representation was used and less prominent when the phrase representations were used. Strategies which generated rules with negation also performed better with respect to binary classification compared to multi-class classification. In comparison with the other machine learning techniques selected, the proposed IRL mechanism was shown to generally outperform all the compared techniques and was competitive with SMO.