12

A Device-Oriented Defi nition of Functions of Artifacts and Its

Perspectives

12.1 Introduction

Functionality is a key aspect of technical artifacts and biological organisms. This chapter
discusses defi nitions of the functionality of technical artifacts from the viewpoint of engi-
neering design and ontological engineering. In engineering, much research on functionality
has been conducted in areas such as functional representation (e.g., Chandrasekaran, Goel,
and Iwasaki 1993; Chittaro et al. 1993), engineering design (e.g., Hubka and Eder 1988;
Umeda et al. 1996; Hirtz et al. 2002), and value engineering (e.g., Miles 1961). Such
research aims at establishing a modeling framework for computer models of artifacts from
the teleological viewpoint (functional models), which can be used in engineering activities
such as design and diagnosis. There have been many fundamental discussions on the
functionality of artifacts, although there is no common defi nition of functions (Chan-
drasekaran and Josephson 2000; Hubka and Eder 2001; Stone and Chakrabarti 2005).
Such discussions in the fi eld of engineering are motivated by the requirements placed
on functional models, such as the consistency, reusability, and composability of the pieces
that make up models. In practical situations engineers tend to describe functional models
in an ad hoc way. Functions can be captured in different ways in different domains. To
satisfy the above requirements, a prescriptive defi nition of functions is needed. Such a
defi nition aims at giving authors of the functional models a conceptual schema and guide-
lines to restrict the viewpoint for describing the functions of target artifacts.
In this chapter, we fi rst discuss our device-oriented defi nition of functions (Kitamura et
al. 2002, 2006; Kitamura, Koji, and Mizoguchi 2006) as a defi nition of functions for
engineering. Our defi nition of functions is prescriptive from the viewpoint of engineering
devices; by intention, it describes only one kind of function. An important element of the
prescriptive defi nition is the defi nition of the behavior of devices as a basis of functions.
Then we show our defi nition of functions as a role played by a behavior (in that sense)
under a context of use. We categorize functions into “component functions” and “external
functions” according to the context of use. According to the essentiality to identity of
the device performing the function, accidental functions are distinguished from essential

Yoshinobu Kitamura and Riichiro Mizoguchi