“…First attempts to exploit prior conceptual 7 knowledge in propositional 8 machine learning (as research field predating present-day mainstream KDD) were often restricted to intra-attribute value (typically, taxonomical) structuring [5,8,31,43]. More sophisticated and abstract knowledge models were however sometimes also used to constrain the search and structure the learning workflow; examples are qualitative models by Clark & Matwin [14] or problem-solving methods [17,46]. This effort naturally intensified with the rise of semantic web technologies, providing standard, web-oriented languages and reasoning tools for ontological knowledge (in particular, in OWL [1] and Topic Maps [19]).…”