15. task models


Complete the tea-making manual in Figure 15.7. Do you think it would be useful? Think of situations where such a manual would be helpful and where a more conceptual manual would be better.


Although a manual for tea making might be regarded as a little extreme, such manuals are useful in several situations. You could pose this exercise, together with the initial task analysis, for different domains where more of the following situations are pertinent.

The first situation where a procedural manual is useful is for the absolute novice who has no idea of the conceptual background. This might be a first-time user, or when an activity is performed very infrequently. A good example of the latter is the installation of computer equipment, which most users perform only once every couple of years. Similarly, recipe books are laid out in a highly procedural fashion, although unfortunately not always clearly:

Beat the egg whites until they froth,
then put them into a ramekin.
While beating the egg whites, slowly add the white wine.

The second situation where a procedural manual is useful is where there is some sort of safety-critical aspect, and erroneous decisions, even those carefully considered, can be disastrous. Often, in such a situation, the additional stress can cloud judgement and make it far safer to stick to a predetermined drill. Emergency procedures in large chemical or nuclear installations are an example of this -- when an emergency arises the operators are expected to stick closely to the set procedures. The accident at Chernobyl came about in part because the operators felt that they knew enough to override the rule book. Reading a manual in such circumstances may be too time consuming, but an HTA can be used to train the operator to respond automatically. The use of HTA for military training is largely in this vein.

Thirdly, the situation may not be safety critical, but it may be time critical. Much analysis may have gone into discovering the most efficient way to perform a task, and that way is then taught, by rote, to the operators. Although this form of time and motion approach is less likely to be useful in an information intensive job than in a factory (if there!), there are jobs, such as telephony, where it is still important.

Finally, the user may not have sufficient knowledge to understand why a process works, but can follow a set of instructions. This may relate either to the complexity of the task or to the skill of the operator. If one were teaching kitchen craft to mentally handicapped people, then just such a procedural description of tea making would be required.

The problem with such procedural manuals is that they give the operator no real feeling as to why the tasks are performed in the way they are. Whether such a manual is preferred by a novice user depends very much on the user's personality. Some people prefer to have a set of instructions to get them started, whereas others find it very difficult to use something without some sort of conceptual understanding.

The procedural manual really comes unstuck when the set of tasks considered is not complete. When faced with a radically new task the user must understand enough of the domain to perform it ad hoc or to modify an existing procedure. One frequent cause of entirely new situations is unforeseen breakdowns of equipment. For example, if the kettle was broken, one could then abstract that the real reason for boiling the kettle was to heat water and that this could be performed by heating a bowl of water in the microwave oven. Such a modification of the procedure is not even suggested by the procedural manual.

Other exercises in this chapter

ex.15.1 (ans), ex.15.2 (ans), ex.15.3 (ans), ex.15.4 (ans), ex.15.5 (ans), ex.15.6 (tut)

all exercises for this chapter