Knowledge and communication: a tutorial

The subtle interaction between knowledge, action, and communication is an important theme underlying much of the literature on reasoning about knowledge in a variety of disciplines. The purpose of this paper is to review work on the relationship between knowledge and communication in distributed systems. Communication is the basic means by which knowledge is obtained and transferred in a distributed system. As a result, properties of the communication medium play a central role in determining what states of knowledge can result from communication. Most of this paper is a review of theorems that illustrate this connection and a discussion of their implications. In the latter part of this paper, we consider knowledge-oriented programming, a novel approach to describing agents' behavior in a distributed system. Knowledge-oriented programs are an extension of the knowledge-based protocols of Halpern and Fagin, in which communication is abstracted away completely from the description of agents' behavior. In its stead, agents can perform high level actions that are defined in terms of changing the state of knowledge of other agents. Such actions are called knowledge-oriented actions. Communication then enters when we come to implement the knowledge-oriented actions in a given context. Knowledge-oriented programming makes explicit use of the fact that the role of communication is to change the state of knowledge of agents in the system.