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, l