ing natural forces and a dizzying array
of non-technical economic, statutory,
societal, and logical constraints. Software engineering is similar except
that fewer forces involve the natural
˲ Adapting to changing environments.
Most environments that use computing constantly change and expand.
With drawn-out acquisition processes
for complex software systems, it is not
unusual for the system to be obsolete
by the time of delivery. What waste!
Mastering evolutionary development is
the new challenge. 2
The problems surrounding the six issues listed here are in large measure
the consequence of an overly narrow
view of the system for which the software engineer is responsible. Although
controlled by software, the system is
usually a complex combination of software, hardware, and environment.
Platform independence is an ideal
of many software systems. It means
that the software should work under
a choice of operating systems and
computing hardware. To achieve this,
all the platform-dependent functions
are gathered into a platform interface module; then, porting the system to another platform entails only
the building of that module for the
new platform. Examples of this are
the Basic Input-Output System (BIOS)
component of operating systems and
the Java Virtual Machine (JVM). When
this can be achieved, the software engineer is justified in a software-centric
view of the system.
But not all software systems are
platform independent. A prominent
example is the control system for advanced aircraft. The control system is
implemented as a distributed system
across many processors throughout
the structure where they can be close
to sensors and control surfaces. Another example is software in any large
system that must constantly adapt in
a rapidly changing environment. In
these cases the characteristics of the
hardware, the interconnections, and
the environment continually influence
the software design. The software engineer must either know the system
well, or must interact well with someone who does. In such cases adding
We need to encourage
system thinking that
and user environment
as well as software.
a system engineer to the team will be
No matter what process engineers use
to achieve their system objectives, they
must form and manage an engineering
team. Much has been written on this
topic. Software engineering curricula
are getting better at teaching students
how to form and work on effective
teams, but many have a long way to go.
Every software team has four important roles to fill. These roles can be
spread out among several people.
The software architect gathers the
requirements and turns them into
specifications, seeks an understanding
of the entire system and its trade-offs,
and develops an architecture plan for
the system and its user interfaces.
The software engineer creates a
system that best meets the architecture plan. The engineer identifies and
addresses conflicts and constraints
missed by the architect, and designs
controls and feedbacks to address
them. The engineer also designs and
oversees tests. The engineer must have
the experience and knowledge to design an economical and effective solution with a predictable outcome.
The programmer converts the engineering designs into working, tested
code. Programmers are problem-solv-ers in their own right because they
must develop efficient, dependable
programs for the design. Moreover,
anyone who has been a programmer
knows how easy it is to make mistakes
and how much time and effort are
needed to detect and remove mistakes
from code. When the software engineer has provided a good specification,
with known exceptions predefined and
controls clearly delineated, the pro-
grammer can work within a model that
makes the job of implementation less
The project manager is responsible
for coordinating all the parts of the
team, meeting the schedules, getting
the resources, and staying within budgets. The project manager interfaces
with the stakeholders, architects, engineers, and programmers to ensure the
project produces value for the stakeholders.
In some cases, as noted previously,
a systems engineer will also be needed
on the team.
We have not arrived at that point in
software engineering practice where
we can satisfy all the engineering criteria described in this column. We still
need more effective tools, better software engineering education, and wider
adoption of the most effective practices. Even more, we need to encourage
system thinking that embraces hardware and user environment as well as
By understanding the fundamental ideas that link all engineering disciplines, we can recognize how those
ideas can contribute to better software
production. This will help us construct
the engineering reference discipline
that Glass tells us is missing from our
profession. Let us put this controversy
1. denning, P. computing is a natural science. Commun.
ACM 50, 7 (July 2007), 13–18.
2. denning, P., gunderson, c., and hayes-roth, r.
evolutionary system development. Commun. ACM 51,
12 (dec. 2008), 29–31.
3. denning, P. et al. computing as a discipline. Commun.
ACM 32, 1 (Jan. 1989), 9–23.
4. glass, r., Vessey, i., and ramesh, V. research in
software engineering: an analysis of the literature.
Information and Software Technology 44, 8 (2002),
5. riehle, r. an engineering context for software
engineering. Ph.d. thesis, 2008; theses.nps.navy.
6. riehle, r. engineering on the surprise continuum: as
applied to software practice. ACM SIGSOF T Software
Engineering News 30, 5 (sept 2005), 1–6.
7. sangwan, r., lin, l-P, and neill, c. structural
complexity in architecture-centric software. IEEE
Computer (mar. 2008), 96–99.
8. tichy, W. should computer scientists experiment
more? IEEE Computer (may 1998), 32–40.
Peter J. Denning ( firstname.lastname@example.org) is the director of the
cebrowski institute for information innovation and
superiority at the naval Postgraduate school in monterey,
ca, and is a past president of acm.
Richard Riehle ( email@example.com) is a visiting professor
at naval Postgraduate school in monterey, ca, and is
author of numerous articles on software engineering and
the popular textbook Ada Distilled.