A Device-Oriented Defi nition of Functions of Artifacts and Its Perspectives 211
12.2.7 Relations Among Functions and the Way of Function Achievement
We believe that a clear understanding of relationships among functions contributes to a
clear defi nition of function. We can distinguish “part-of” (called “is-achieved-by”) from
“is-a” relations. As pointed out in section 12.2.3 and further discussed in the appendix, in
a system context a function of a system is (or can be) achieved by a series of fi ner-grained
functions of components. (We call these functions a “goal-function” and “method func-
tions,” respectively). Figure 12.2 shows an example of a functional model of an artifact
using such an “is-achieved-by” relation, a so-called function decomposition tree. In the
literature in engineering, similar relation has been captured as a “degree of complexity”
(Hubka and Eder 1988) and as a function decomposition (Pahl and Beitz 1996). This is-
achieved-by relation shows a part of Cummins’s causal role of the components for capacity
of a containing system (Cummins 1975).
Store
coffee
Heat
water
Functional Concept Ontology
(is-a hierarchy of generic functions)
Example of is-a hierarchy of
generic ways of function
achievement for removing entity
Energy functions
Receive Make energy existent
Convert Shift Change
composition
Take Give Transmit
Remove
Separate
Combine
is-a is-a
Ways for removing entity
Phase way Constituent
way
Weight
way
Size way
Centrifugal
separating way
Filter
way
Extraction
way
Distillation
way
Example of a function
decomposition tree
of a coffee maker
(part-of hierarchy)
is-achieved-by
AND
AND AND
Transform electricity
to heat
Give heat
to water
Move
water
Select ground
coffee
Extract coffee taste
Hot fluid way
Filter way
Remove
ground coffee
Mix ground coffee
and water
Heat transfer
Chemical way Physical way
Figure 12.2
Relations among functions.