Page 293 - Design for Six Sigma a Roadmap for Product Development

Axiomatic Design 263

functional structure, the relative difficulty of employed physical
processes, and the relatively large number of assemblies and compo-
nents involved (Phal and Beitz 1988). The term complexity is used in
most of the literature in a pragmatic sense. It is easier to have an idea
about complexity by shaping where it does exist and how it affects
design rather than what it really means. Linguistically, complexity is
defined as a quality of an object. In our case an object is a design entity,
a product, a service, or a process. The object can have many interwo-
ven elements, aspects, details, or attributes that make the whole object
difficult to understand in a collective sense. Complexity is a universal
quality that does exist, to some degree, in all objects. The degree of
complexity varies according to the many explored and understand-
able phenomenon in the object. Ashby (1973) defines complexity as
“the quantity of information required to describe the vital system.”
Simon (1981) defines a complex system as an object that “is made up
of a large number of parts that interact in a non simple way.” These
definitions imply some level of communication between interrelated
(coupled) elements of the complex system, which is translated to one
of the major characteristics of a complex system, hierarchy. Simon
(1981) illustrated that hierarchy has a broader dimension than the
intuitive authority meaning. It reflects some level of communication
or interaction between related entities. In a designed entity, the
higher the level of interaction, the shorter is the relative spatial
propinquity.
In his seminal paper, Weaver (1948) distinguished between two
kinds of complexity: disorganized and organized. Systems of disorga-
nized complexity are characterized by a huge number of variables. The
effects of these variables and their interaction can be explained only
by randomness and stochastic processes using statistical methods
rather than by any analytical approach. The objective is to describe the
system in an aggregate average sense. Statistical mechanics is a good
example of a discipline that addresses this type of complexity.
Analytical approaches work well in the case of organized simplicity,
which is the extreme of the complexity spectrum at the lower end.
Organized simplicity systems are characterized by a small number of
significant variables that are tied together in deterministic relation-
ships. Weak variables may exist but have little bearing in explaining
the phenomena. (Refer to Sec. 3.7.)
The majority of design problems can’t always be characterized as
any of the two complexity extremes that have been discussed. It is
safe to say that most problems often belong to a separate standalone
category in between the two extremes called the organized complexity.
This category of problem solutions utilizes statistical and analytical
methods at different development stages. Design problems are more