To make the following presentation more precise, we use the simple hypothetical reasoning framework of Theorist . ``Vanilla'' Theorist is defined in terms of , a set of closed formulae, called the ``facts'', and , a set of (possibly open) formulae called ``possible hypotheses,'' or assumables. The following definitions are relevant:
As pointed out in Csinger and Poole , there's more than one way to use such a hypothetical reasoning formalism. You can use it at least for prediction and for abduction, often in a single domain or problem.
We can also distinguish between two types of tasks to which these different reasoning strategies may be applied:
The distinction between design and recognition turns on whether the system is free to choose any hypothesis that it wants or whether it must try to ``guess'' some hypothesis that ``nature'' or an adversary has already chosen. A scheduling agent is free to choose the time of a meeting subject to known constraints, while other agents wishing to attend the meeting need to discover when it will be held; the scheduling agent is engaged in a design task, while the attending agents are performing a recognition task. Note that these frameworks are different ways to use the same formal system for different purposes. In order to use the system we have to choose one way to implement our domain.
In what follows, we choose to recognize models of users by abduction, and to design presentations for them also by abduction.