Path: utzoo!utgpu!news-server.csri.toronto.edu!qucis!skill
From: skill@qucis.queensu.CA (David Skillicorn)
Newsgroups: comp.software-eng
Subject: Overengineering Software
Message-ID: <1828@qusunita.queensu.CA>
Date: 26 Apr 91 14:17:10 GMT
Organization: Queen's University, Kingston, Ontario, Canada
Lines: 26

A number of people have used metaphors for the robustness of software
based on physical processes such as bridge building. Such metaphors
contain some dangers since they tend to suggest that building software
is much like building bridges, and building in a little extra something
will increase the <insert nice property here> of the software.

The problem is that (all things being equal) real world systems are
continuous and have the property that a little bit more of something
in the building results in a little bit more of a nice property in
the final system. Software is not continuous and such properties are
uncommon and hard to work with. Two behaviours of the system that
are perceived by users to be very close by some appearance metric
may be wildly different in some metric suitable to the internal logic
of the program. 

Now it is possible to talk about the robustness of software in
terms of the size of the set of input/output states for which the
software is well-behaved; and hence in terms of predicates which
can be "weaker" or "stronger". But this doesn't seem to be quite what
people mean when they talk about "pushing the software". And, as
I've already suggested, it doesn't necessarily correspond very directly
to the external appearance of a "stronger" piece of software.

                           David Skillicorn
                           Queen's University