Information Technology Reference
In-Depth Information
incredibly large scale would appear to have been highly motivated by the need to
increase manufacturing volume drastically during the Second World War.
Perhaps one of the most visible examples of designing around reusable com-
ponents that can be encountered in the current era is that of the motor car. While a
given manufacturer's models may differ substantially in appearance, many ele-
ments such as switches, instruments, starter motors etc. will be common across
manufacturers. Design reuse is also (if less visibly) used very successfully in such
domains as electronics, as well as in the building industry (for example, through
the standardization of dimensions for windows, doors, pipes), and in many other
domains. The motivation may well be ease of both manufacturing and mainte-
nance. While the former is more relevant to software, the latter may also be a
significant factor when viewed across the often-long lifetimes of software prod-
ucts, even if maintenance of these is interpreted in a rather different way.
While such reuse may often be centered upon quite small elements, larger, pos-
sibly composite, ones are reused too (car engines provide a good example). However,
there are two important characteristics of such reuse that we need to note here.
• The first is that it is commonly based upon well-defined functionality. Most
physical components have very well defined roles (starter motor, pump, switch,
etc.), making it easy for the designer to identify the appropriate manufacturer's
catalogues, and then search them in order to view what is available to them.
• The second is that the elements themselves have well-defined interfaces. Indeed,
an important corollary of this is that there may also be several manufacturers
who are able to provide a given component ('second sourcing'). Substitution
may be an exact functional and non-functional match (as it tends to occur for
integrated circuits), or may differ slightly in terms of non-functional charac-
teristics, while still conforming to the specified interface.
These are not accidental properties, but rather ones that are driven by several
economic factors. These include the need to minimize the cost of manufacturing an
item, pressure to maintain a marketplace position, and the user's need to protect
their supply chain (here the 'user' is another manufacturer who makes use of a
given component for integration into their own product). Sometimes the standards
necessary to enable this emerge from marketplace factors, leading to the accep-
tance of one manufacturer's format as a standard for all; at other times an industry
may set up a standards body to undertake the role of agreeing standards. Whatever
the route leading to the standards, there is significant pressure on manufacturers to
conform to them. For the engineering designer, as mentioned above, catalogues of
components are now readily available in many domains, with examples ranging
across electronic and electrical, to mechanical and civil engineering. However, the
ways in which these catalogues are used during the design process appear to be a
rather more elusive concept. A good example of this is given in Pugh, which
provides the following quotation from Cooke:
The designer of electronic-based products has available an enormous range of basic
building blocks of high or still increasing complexity. What he often does not have is
