## What Can Machines Know? On the Properties of Knowledge in Distributed Systems (1996)

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Venue: | Journal of the ACM |

Citations: | 49 - 8 self |

### BibTeX

@ARTICLE{Fagin96whatcan,

author = {Ronald Fagin and Joseph Y. Halpern and Moshe Y. Vardi},

title = {What Can Machines Know? On the Properties of Knowledge in Distributed Systems},

journal = {Journal of the ACM},

year = {1996},

volume = {39},

pages = {328--376}

}

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### Abstract

It has been argued that knowledge is a useful tool for designing and analyzing complex systems. The notion of knowledge that seems most relevant in this context is an external, information-based notion that can be shown to satisfy all the axioms of the modal logic S5. We carefully examine the properties of this notion of knowledge and show that they depend crucially, and in subtle ways, on assumptions we make about the system and about the language used for describing knowledge. We present a formal model in which we can capture various assumptions frequently made about systems, such as whether they are deterministic or nondeterministic, whether knowledge is cumulative (which means that processes never "forget"), and whether or not the "environment" affects the state transitions of the processes. We then show that under some assumptions about the system and the language, certain states of knowledge are not attainable and the axioms of S5 do not completely characterize the pr...