A probabilistic approach to rough set theory with modal logic perspective

We propose the notion of probabilistic information system (PIS) to capture situations where information regarding attributes of objects are not precise, but given in terms of probability. Notions of indistinguishability relations and corresponding approximation operators based on PISs are proposed and studied. It is shown that the deterministic information systems (DISs), incomplete information systems (IISs) and non-deterministic information systems (NISs) are all special instances of PISs. Moreover, the approximation operators defined on DIS (relative to indiscernibility), IISs and NISs (relative to similarity relations) are all originated from a single approximation operator defined on PISs. Further, a logic LPIS for PISs is proposed that can be used to reason about the proposed approximation operators. A sound and complete deductive system for the logic is given. Decidability of the logic is also proved.