The expert system uses an architecture-based design to apply the same knowledge to different machines. An architectural model of the machine is constructed when the session begins. This model is used to determine which tests are applicable, the components that compose the machine, and how the machine should be fixed.
All inference is done by matching.
No search or backtracking is performed. A diagnosis is interactively developed by first having the user pick among problem descriptions. The expert system then refines this by asking the user questions. For instance, the user is asked to examine hardware connections, run tests and report on error messages. If the expert system still can not classify the problem it requests further tests or presents a new problem classification.