Human-Computer Interaction 3e Dix, Finlay, Abowd, Beale

exercises  -  15. task models

EXERCISE 15.1

The following is a list of objects found in one of the authors' kitchens:

teapot, mug, soup bowl, plate, spoon, table knife, cook's knife, fork, saucepan, frying pan, kettle, casserole, fish slice, tin opener, baking tray, scales, mixing bowl, glasses, jugs, corkscrew, rolling pin, ladle, egg cup, chopping board.

Produce a taxonomy using the TDH notation of these objects. Does it obey the TAKD uniqueness rule? Compare your answer with someone else's. (Note: the authors had great difficulty with items like the corkscrew, which did not fit easily into any generic category - perhaps you did better.)

answer

As the authors had already produced a partial taxonomy, we interviewed two domain experts (cooks). They were asked to describe how they would group and classify the kitchen items. They were explicitly told (and reminded) that they could have multiple classifications and put the same item into several categories. The authors then cast their answers into TDH notation.

One of the subjects was a doctor and used to medical taxonomies of disease. Despite stressing the looseness of the classifications, he insisted on a complete taxonomic tree (Figure Ex15.1.1).

kitchen object XOR
|__  preparation XOR
|    |__  pre-preparation XOR
|    |    |__  opening
|    |    |         tin opener, cork screw
|    |    |__  measuring
|    |              scales, (measuring) jug
|    |__  'proper' preparation XOR
|         |__  active
|         |         rolling pin, cook's knife, (cook's) spoon
|         |__  passive
|                   mixing bowl, chopping board
|__  cooking XOR
|    |__  passive
|    |         teapot
|    |__  active XOR
|         |__  external power
|         |         saucepan, frying pan, casserole, baking tray
|         |__  internal power
|                   (electric) kettle
|__  serving XOR
     |__  serving
     |         fish slice, (serving) jug, ladle
     |__  eating XOR
          |__  active
          |         spoon, fork, knife}
          |__  passive XOR
               |__  food
               |         egg cup, soup bowl, plate
               |__  drink
               |         mug, glass

Figure Ex15.1.1 - TDH taxonomy produced by first subject

As you see all his branches are XOR branches. On discovering that 'jug' had to fit in two places in his taxonomy, he split it into 'serving jug' and 'measuring jug'. This emphasises the need for the task analyst rather than the domain expert to actually draw up the taxonomy!

As it is a true tree it clearly does not satisfy the uniqueness rule, but the only way it could is to invent spurious new categories. One could under 'opening' add categories for 'bottles' (containing corkscrew) and tins (containing tin opener), but this would not improve clarity.

If the first subject was a stickler for precision, the second subject preferred broad categories. Figure Ex15.1.2 shows her initial classification.

kitchen object OR
{__  things for making tea
{         teapot, mug, kettle, spoon
{__  things for eating meals
{         soup bowl, plate, glasses, egg cup
{__  cutlery for meals
{         spoon, table knife, fork
{__  cutlery for cooking
{         spoon, fork, fish slice, tin opener, table knife,
{         corkscrew, rolling pin, ladle
{__  things for making meals
{         saucepan, frying pan, casserole, baking tray, scales,
{         mixing bowl, jugs, chopping board
{__  things for serving meals
          jugs, casserole, fish slice, corkscrew, ladle, spoon

Figure Ex15.1.2 - Initial version of TDH taxonomy produced by second subject

We wanted to put some additional structure on this and so, after some discussion, the subject agreed that her basic distinctions were those of function ('making meals' etc.) and between cutlery and non-cutlery. Using these to form an AND branch, we obtained Figure Ex15.1.3.

kitchen object AND
/__  material XOR
/    |__  cutlery
/    |         spoon, table knife, fork, fish slice, tin opener
/    |         corkscrew, rolling pin, ladle
/    |__  non-cutlery
/              teapot, mug, kettle,
/              soup bowl, plate, glasses, egg cup,
/              saucepan, frying pan, casserole, baking tray, scales,
/              mixing bowl, jugs, chopping board
/__  function OR
     {__  making tea
     {         teapot, mug, kettle, spoon
     {__  cooking meals
     {         spoon, fork, fish slice, tin opener, table knife,
     {         corkscrew, rolling pin, ladle,
     {         saucepan, frying pan, casserole, baking tray, scales,
     {         mixing bowl, jugs, chopping board
     {__  serving meals
     {         jugs, casserole, fish slice, corkscrew, ladle, spoon
     {__  eating meals
               soup bowl, plate, glasses, egg cup,
               spoon, table knife, fork

Figure Ex15.1.3 - Refined version of TDH taxonomy produced by second subject

This taxonomy does not obey the uniqueness rule either; for example, fish slice and ladle always appear together. In terms of KRG they are both:

     kitchen object/material(cutlery)/
                             function{cooking meals,serving meals}/

The TAKD purist might demand extra categories to fulfil the uniqueness rule. However, the authors would recommend that students simply be taught to recognise the rule and use it as a heuristic.

It is interesting that both domain experts focused on the functional view of the items, just as the authors did in the book. This suggests that it is indeed a generic way of classifying kitchen objects and would thus be a good candidate for classification in a catalogue or menu system. The second subject also noted that her original breakdown was inspired, not so much by the function per se, but by where the items were stored in her kitchen - itself determined largely by function. This is perhaps the physical equivalent of a menu system!


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


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