An Automatic System for Modality and Negation Detection

The article presents the experiments carried out as part of the participation in the pilot task (Modality and Negation)1 of QA4MRE@CLEF 2012. Modality and Negation are two main grammatical devices that allow to express extra-propositional aspects of meaning. Modality is a grammatical category that allows to express aspects related to the attitude of the speaker towards statements. Negation is a grammatical category that allows to change the truth value of a proposition. The input for the systems is a text where all events expressed by verbs are identified and numbered the output should be a label per event. The possible values are: mod, neg, neg-mod, none. In the developed system, we first build a database for modal verbs of two categories: epistemic and deontic. Also, we used a negative verb list of 1877 verbs. This negative verb list has been used to identify negative modality. We extract the each tagged events from each sentences. Then our system check modal verbs by that database from each sentences. If any modal verbs is found before that an event then that event should be modal verb and tagged as mod. If modal verb is there and also negeted words is found before that evet then that event should negeted mod and tagged as neg-mod. If no modal verb is found before that an event but negeted word are found before that event then that event should be negeted and tagged as neg. Otherwise the event should tagged as none. We trained our system by traing data (sample data) that was provided by QA4MRE organizer. Then we are tested our system on test dataset. In test data set there are eight documents, two per each of the four topics such as Alzheimer, music and society, AIDs and climate change. Our system overall accuracy is 0.6262 (779 out of 1244).