Diagnostics and a qualitative model

First generation expert systems were using shallow knowledge based on heuri stic information to solve a diagnostic problem. This approach has many disa dvantages, which can be avoided by using deep knowledge. Diagnostic reasoni ng based on deep knowledge is called model-based diagnostics. Recently, the use of qualitative modeling in relation to deep knowledge in expert system s has become increasingly important. The main purpose of our contribution i s to present the model-based diagnostic approach at a formal level. The ori ginality of the presented formalization is the concept of the diagnostic sp ace, the characterization of the minimal diagnoses, and the measurement. Th e formalization serves as the theoretical background to prove our view to t he design of qualitative system models and to establish the diagnostic arch itecture called DISY. The qualitative system model in our diagnostic approa ch needs not to be specially adopted for use in the diagnostic domain. The only requirement is that it must simulate the system behavior expressed by normal or abnormal functioning of its components. Proposed DISY architectur e is not complex and simply takes into an account the previous diagnostic r esult to obtain a new one from the additional observation-measurement (medi cal tests or examinations) of the system. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.