Qualitative reasoning in planning involving processes

An intelligent agent, operating in an external world which cannot be fully described in its internal world model, must be able to monitor the success of a previously generated plan and to respond to any errors which may have occurred. The process of error analysis requires the ability to reason in an expert fashion about processes operating in the world, since the direct effects of a plan action can be completely specified when the plan is generated, but the indirect effects cannot. For example, the action `open tap´ leads with certainty to `tap open´; whereas whether there will be a fluid flow and how long it might last is more difficult to predict. After a brief survey of the problems faced by existing planners, the paper describes the qualitative reasoning incorporated in a planning system called EXCALIBUR. The techniques may ultimately be useful in process control, manufacturing and production