MAKING THE ABSTRACTION HIERARCHY CONCRETE

The abstraction hierarchy (AH) is a multileveled representation framework, consisting of physical and functional system models, which has been proposed as a useful framework for developing representations of complex work environments. Despite the fact that the AH is well known and widely cited in the cognitive engineering community, there are surprisingly few examples of its application. Accordingly, the intent of this paper is to provide a concrete example of how the AH can be applied as a knowledge representation framework. A formal instantiation of the AH as the basis for a computer program is presented in the context of a thermal-hydraulic process. This model of the system is complemented by a relatively simple reasoning mechanism which is independent of the information contained in the knowledge representation. This reasoning mechanism uses the AH model, along with qualitative user input about system states, to generate reasoning trajectories for different types of events and problems. Simulation outputs showing how the AH model can provide an effective basis for reasoning under different classes of situations, including challenging faults of various types, are presented. These detailed examples illustrate the various benefits of adopting the AH as a knowledge representation framework, namely: providing sufficient representations to allow reasoning about unanticipated fault and control situations, allowing the use of reasoning mechanisms that are independent of domain information, and having psychological relevance. © 1994 Academic Press, Inc.