13 - Dynamic Epistemic Logic (Update of Chapter 12)

Abstract

This chapter presents an overview of dynamic epistemic logic (DEL). Groeneveld characterizes DEL as being dynamic, multiagent, and higher order. It is dynamic since its focus is on information change. It is multiagent because the phenomena studied in DEL, such as communication, usually involve more than one agent. It is higher order in the sense that the information an agent has about the world (which contains other agents) includes information about the other agents' information: higher-order information. In short, DEL aims to track the (higher-order) information of many agents as information flows. The starting point of DEL is epistemic logic: the logic of knowledge. One of the key features of epistemic logic is that the information states of several agents can be represented by a single Kripke model consisting of a set of states, a set of accessibility relations, and a valuation. In DEL, information change is modeled by transforming Kripke models. Since DEL is mostly about information change due to communication, the model transformations usually do not involve factual change. The bare physical facts of the world remain unchanged, but the agents' information about the world changes. In terms of Kripke models this means that the accessibility relations of the agents have to change.