Clarify the scope of objects to be sorted.
Decide upon a perspective regarding classifications that
matches the objective.
It is important that the perspective is one that places
every object into a specific category, with no single object
belonging to two different categories, and that objects can
be sorted without dropouts or overlapping.
Find as many conditions as possible for representing clas-
sifications, and consider the value of these classifications.
One can sometimes combine a number of categories into
larger classifications.