212 Yoshinobu Kitamura and Riichiro Mizoguchi
It is important for defi ning function to discriminate functions from “way of function
achievement.” A way of function achievement for a function shows background knowl-
edge of the is-achieved-by relation such as physical principles and theories (Kitamura
et al. 2002). The way of achievement helps us detach “how to achieve” (way) from “what
is intended to achieve” (function). For example, “to weld something” should be
decomposed into the “joining function” and “fusion way.” This increases the generality
and capacity of a functional model in that it accepts a wide range of ways to perform a
function, such as using a bolt and nut to achieve the same goal. A feature of function
decomposition can also be found as a “means” in Malmqvist (1997). We identify is-a
relations between generic ways of function achievement. Figure 12.2 shows a portion of
the is-a relations hierarchy of generic ways of function achievement for removing entities.
The fi lter way used in the coffeemaker is a subtype of the “size way” and the “physical
way.” Such a knowledge base can be used by engineers to explore alternative ways to
achieve a required function (Kitamura et al. 2006; Kitamura, Koji, and Mizoguchi
2006).
On the other hand, an is-a relation among generic functions (also called “a-kind-of,”
“categorization,” “subsumption,” etc.) shows abstraction of “what to achieve.” We devel-
oped an ontology of generic types of functions (called “a functional concept ontology”)
with is-a relations (Kitamura et al. 2002). Figure 12.2 shows a portion of the is-a hierarchy
of the generic types.
12.3 Perspectives for Capturing Functions and Categories of Functions
12.3.1 Overview and Approach
The defi nition of function in section 12.2 is strictly from the device-centered viewpoint,
which is intended to prescribe guidelines for functional modeling of artifacts. Other types
of functions, however, still remain to be investigated. Toward a more general account, this
section discusses rather descriptive defi nitions of other kinds of functions.
To categorize functions, we generalize the device-oriented basic model discussed in
section 12.2.2 into a generalized basic model. In the generalized model, a physical entity
(agent) affects a target thing (operand) at a location. Thus a state of the operand changes
in a time interval. The change, called an effect, is represented as a combination of the
initial state s 1 at the start time point t 1 and the fi nal state s 2 at the fi nal time point t 2. Such
an effect is a generalized type of the device-oriented behavior discussed in section
12.2.2.
The change (effect) plays a goal-oriented role under a goal-oriented context. The goal-
oriented context consists of a teleological context and an effect context. The teleological
context is related to the user’s intention, as discussed in the following section. The effect
context specifi es the focused-on area in the model for capturing a role. By specifying the