Non-first-order features in concept languages

In this paper we propose an epistemic concept language, where the epistemic operator is interpreted in terms of minimal knowledge. We show that the proposed formalism provides an adequate characterization of many non-rst-order aspects of frame-based knowledge representation systems, by admitting in the knowledge base various forms of epistemic sentences. In particular, we address the formalization of defaults and role closure. We argue that the minimization of knowledge captures intuitive and natural forms of reasoning that arise by restricting the attention to the individuals that are known to the knowledge base. Many of these forms of reasoning are actually provided by several knowledge representation systems, whose implementation is object centered.