A Device-Oriented Defi nition of Functions of Artifacts and Its Perspectives 215
12.3.4 Effect on State or Process
According to the target thing changed by the effect, the device function is categorized into
an effect-on-state function and an effect-on-process function, as shown in fi gure 12.3. The
effect-on-state function refers to changes in physical attributes of a target thing. Its sub-
types are; the fl owing-object function, which corresponds to a base-function discussed in
section 12.2.2, and the inter-device function, which refers to changes of another device.
The latter’s example is a rod’s function “to push cam.” The cam is another device, which
is not considered as objects fl owing through the rod.
The effect-on-process function is based on an effect on a process or change. A
behavior as the basis of the device function can be regarded as a kind of a process.
It has a subtype, the effect-on-function function, whereby a function plays a specifi c
role for another function. The effect-on-function function is further categorized
into a causal-meta function and partial-achievement function. The former corresponds
to meta-functions such as ToDrive and ToEnable (Kitamura et al. 2002), which are
collaborative roles played by a base-function for another base-function. The latter is
performed by a method function for a goal function in the “is-achieved-by” relation
discussed in section 12.2.7. It is categorized into an essential-part function and a supple-
mentary-part function according to whether the contribution is mandatory or not. The
distinction between primary and secondary functions (Pahl and Beitz 1996) is similar to
this.
12.3.5 Negative Goal and Kinds of Time Interval
There are some categories of functions that are based on adding more descriptors to the
categories discussed thus far. A negative function (as an antonym of positive function) is
one of them, which has a goal to prevent a specifi c state (or a process) from occurring.
The following two functions of a paperweight have a negative goal and a normal goal,
respectively.
“A paperweight prevents a piece of paper from moving.” (Negative function)
“A paperweight exerts vertical force on a piece of paper.” (Positive function)
The effects are represented as changes in the values of attributes in a time interval. The
same effect can imply different meanings for different kinds of time intervals. For example,
an increasing-temperature function of a heater can imply the following:
“A heater increases the temperature of the air at a specifi c location in a room.”
(Absolute-functioning time function)
“A heater increases the temperature of the air at the output port to higher than that at
the input port.” (Flowing-object-functioning time function)