Within opinion mining, several subtasks can be identified, all of them having to do with tagging a given document according to expressed opinion: 1. determining document subjectivity, as in deciding whether a given text has a factual nature (i.e.
while for the former we use well-known learners for binary classification (the naive Bayesian learner using the multinomial model (McCallum and Nigam, 1998), support vector machines using linear kernels (Joachims, 1998), the Rocchio learner, and its PrTFIDF probabilistic version (Joachims, 1997)), for Approach III we use their multiclass versions 9 .