Research On The Dynamics Of Constrained Epistemic Default Theory

The knowledge of the world is characterized by a default theory, which consists of a set of consistent formulae (the facts) and a set of default rules representing plausible assumptions. Extensions are models of the world described by default theories.Default logic is a prominent rigorous method for reasoning with incomplete information based on assumptions. It is a static approach, in the sense that it doesn't reason about changes and their consequences. On the other hand, its nonmonotonic behavior appears when changes to a default theory are made. A dynamic method was proposed by Antoniou. The operations of contraction and revision were considered and their properties were studied.Based on previous works, constrained epistemic default logic (CEDL) is proposed in this paper. Knowledge is distinguished from belief by adding the modality words K (know) and B (believe). Due to the constrained condition, the CEDL is semi-monotonic and guarantees the existence of extensions. Some concepts such as new knowledge, valid knowledge, rejection by knowledge, new constrain and rejection by constrain are defined for CEDL. The focus of the work is how to make the change of knowledge and constrain update without having to recaculate the extensions of the changed default theory from scratch. The properties and acquisition of the extension in CEDL are studied and related theorems are proved. Further, this paper studies the dynamic behavior of CEDL in the face of changes with knowledge and constrain. The epistemic process is built to describe the agent's dynamic characteristics. It is concluded that the agent will get the complete cognition about some specific problem when continual changes with knowledge and constrain are made. Finally, the work is compared with the related work and the future work is discussed.