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2. DIAGNOSTIC TECHNIQUES AND METHODSIt is advisable and, sometimes, essential to have a sound understanding of system organization, that is, its structure and the relations and interactions between subsystems and/or components, to make a correct diagnosis. Structure can be used in a top-down approach to determine function. For example, given a structural description of a cistern, physical principles can be used to simulate its behavior and infer its function, which requires descriptions of its components. Taking a bottom-up approach, the required function may suggest what structures could be used. For example, if we know that the ball of the cistern must float in water, we can conceive of replacing this structure with any other that behaves in the same way. Basically, understanding a mechanism requires an insight into how its structure implements its function. However, often, as is the case in anatomy or the structure of animal systems, this is not fully understood and several partial models have to be combined, which may give rise to inconsistencies. As shown in Table 1, there are a series of techniques and method for conducting automated diagnostics. Each one has its advantages and drawbacks, but they all have one common characteristic: their limitation. Indeed, each individual technique resolves at best only one aspect of the diagnostic problem. So, they need to be integrated individually or collectively into a knowledge-based system for synergetic use. 3. DIAGNOSTICS CONCEPTUALIZATIONAs pointed out by Pepper (1990), "All human diagnosticians, whether they work in automotive repair or medicine, have certain characteristics in common. Both groups have an internal mental model of the task domain. This model is a body of knowledge about the parts of the mechanism or organism they are trying to fix and about how those parts fit together. This model is closely tied to two additional knowledge sources: the expert's formal understanding of the laws of the domain (such as electrical theory) and a large loosely structured body of knowledge consisting of common sense and experience gained simply by living in the world. Taken together, these three knowledge sources are very powerful and enable human beings to solve new problems by reasoning them through..." So, regardless of the type of diagnostics performed, industrial or medical and so on, the same method can be used to conceptualize the diagnostician's internal mental model. Therefore, this section first gives a declarative description of what conceptualization is and then how it is performed, showing the different stages, steps, and actions to be completed.
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