214 Yoshinobu Kitamura and Riichiro Mizoguchi
kind of the goal-oriented role under the unintended context. The causal process of faults
can be represented as a goal-oriented achievement structure for (quasi-)goals. This is used
for failure mechanism modeling (Koji, Kitamura, and Mizoguchi 2005).
12.3.3 Device and Environmental Functions
The general function discussed in section 12.3.2 is categorized into the effect function and
the quasi-function (we will discuss this in section 12.3.6) as shown in fi gure 12.3. The
effect function is based on an effect, which represents temporal changes in attributes of
an external thing other than the agent. Its agent is either a device or a function.
The effect function is further categorized into a device function and an environmental
function. The former represents changes in entities within the system boundary. The latter
includes changes outside of the system boundary, especially those related to users or user
actions. For example, an electric fan performs the following two functions:
“An electric fan moves air.” (Device function)
“An electric fan cools the human body.” (Environmental function)
In the latter, the cool-down effect by the moving air as an output of the electric fan
device is on the human body and thus outside of the system boundary. The environmental
function has two subtypes; a physical environmental function and an interpretative func-
tion. The former means physical changes in the system like the cooling function of the
fan, while the latter sets up one of necessary conditions for cognitive interpretation. For
example, an analog clock has the following two functions. The latter requires someone’s
cognitive interpretation.
“A clock rotates hands (in the specifi c and constant rate).” (Device function)
“A clock informs about time.” (Interpretative function)
Chandrasekaran and Josephson (2000) discuss a similar kind of function, called an
“environment function,” as an effect on the environment (the surrounding world of the
device). Some researchers distinguish purpose from function (e.g., Chittaro et al. 1993;
Rosenman and Gero 1998), whereby the purpose represents a human-intended goal in a
similar sense to this environmental function or interpretative function. We are extending
our framework to include user actions as well (van der Vegte et al. 2004).
Dipert (2006) points out goal-dependence as follows: “... even components of artifacts
have multiple and quite distinct functions.... Instead, they have a function with respect
to an overall goal of some agent and with respect to a level of description.” He shows
some examples of a button on a DVD player, which we categorize into environmental
functions. These include the designer’s purposes and purposes of individuals higher in the
corporate hierarchy as well as the user’s purpose.