This process can be repeated several times, each time asking the expert to perform a different grouping.
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Also, different experts can be asked and their groupings compared.
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Alternatively, one can ask the expert to arrange the cards on a tabletop.
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This allows the expert to cluster the cards (showing similarity) and to use the spatial arrangement in order to give a classification by two attributes.
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Again, the expert can be questioned after the event as to why the particular arrangement was used.
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A range of similar techniques can be used to elicit the user’s or expert’s knowledge about a task.
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Each object/action can be ranked against each task depending on how important the expert thinks they are for that task.
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Perhaps on a scale 0 (never used) to 10 (essential).
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So, for example, if the task were ‘making an omelette’ eggs would be scored 10, but the fork to beat the eggs may only be scored 5.
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Alternatively, the expert can simply be asked to rank the objects, as this may be easier than an absolute judgment.
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However the classification and production of hierarchies is performed, the job of producing possibly large taxonomies and hierarchy diagrams is not trivial.
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This can be done by hand on paper or using a standard word processor, but is easier if an outliner is used.
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There are several commercial outlining tools, and most word processors and many spreadsheets have outlining facilities.
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These outliners make it easy to shift partially sorted groups as we refine the classification.
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They also allow us to hide unwanted information, say when we want to look at the top levels of decomposition of a task hierarchy, or if we want to ‘cut’ a TDH taxonomy to look at generic objects or actions.
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