Epistemic Actions

The previous chapter dealt with public announcements. There are various more complex ‘updates’, or, as we call them, epistemic actions. This chapter introduces a language and logic for epistemic actions. Public announcements are epistemic actions that convey the same information for all agents. They result in a restriction of the domain of the model and therefore in a restriction of the corresponding accessibility relations. More complex epistemic actions convey different information to different agents. They may result in the refinement of accessibility relations while the domain of the model remains unchanged, and they may even result in the enlargement of the domain of the model (and its structure), even when the complexity is measured by the number of non-bisimilar states. We start with a motivating example. Reconsider Example 4.1 on page 67 of the previous chapter ‘public announcements’.