Towards a Logic of Perishable Propositions

Reasoning with uncertain information is a central issue for Artificial Intelligence and Information Systems. Consequently, a vast amount of studies and results devoted to this issue can be found in the literature.Curiously, reasoning with information whose uncertaintyvaries along time cannot be found so much in the literature. Dynamic reliability is a feature found rather frequently in many problems, e.g. in financial markets, meteorology and demographics.In this article we consider propositions whose information about truth evaluation is gradually lost with time. Our motivation has come from the information system under development within the project SIDAM—Distributed Information Systems for Mobile Agents (supported by FAPESP, grant 98/06138-2)—to provide citizens with information about urban automotive traffic in a large city.We propose functions of loss of information, and show how they can be used to characterize the obsolescence of propositional information in a logical system.