An information system collects and processes data withthe aim to extract information and to support decision-making tasks. Since the advent of the so-calledSocialWeb, users are encouraged to create content and uploadit on the Web, so huge amounts of data are continuouslygenerated. This data represents a great opportunity forresearchers, companies, and decision makers to infer non-trivial patterns and generate new knowledge; on the otherside, a lot of challenges arise from such amounts of data. Inorder to handle these new challenges and accomplish theirobjectives, information systems need efficient and effectiveways to process this data. On the one hand, the algorithmsthat process these large amounts of data should have lowcomputational costs, in order to keep up with the rapidevolution of the Web and guarantee efficiency, while onthe other hand they should be able to filter out the lessuseful chunks of data and process only those that lead to aneffective decision making.