Conditional events with vague information in expert systems

Ad hoc techniques and inference methods used in expert systems are often logically inconsistent. On the other hand, among properties and assertions concerning handling of uncertainty, those which turns out to be well founded can be in general easily deduced from probability laws. Relying on the general concept of event as a proposition and starting from a few conditional events of initial interest, a gradual and coherent assignment of conditional probabilities is possible by resorting to de Finetti's theory of coherent extension of subjective probability. Moreover, even when numerical probabilities can be easily assessed, a more general approach is obtained introducing an ordering among conditional events by means of a coherent qualitative probability.