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10.2 Systems engineering 273

less time to talk with them. From a doctor’s perspective, this system was not an
improvement on the previous manual system; from a manager’s perspective, it was.
The nature of security and dependability attributes sometimes makes it even more
difficult to decide if a system is successful. The intention of a new system may be to
improve security by replacing an existing system with a more secure data environ-
ment. Say, after installation, the system is attacked, a security breach occurs, and
some data is corrupted. Does this mean that the system is a failure? We cannot tell,
because we don’t know the extent of the losses that would have occurred with the old
system, given the same attacks.

10.2 Systems engineering

Systems engineering encompasses all of the activities involved in procuring, speci-
fying, designing, implementing, validating, deploying, operating, and maintaining
sociotechnical systems. Systems engineers are not just concerned with software but
also with hardware and the system’s interactions with users and its environment.
They must think about the services that the system provides, the constraints under
which the system must be built and operated, and the ways in which the system is
used to fulfill its purpose or purposes.
There are three overlapping stages (Figure 10.4) in the lifetime of large and com-
plex sociotechnical systems:

1. Procurement or acquisition During this stage, the purpose of a system is
decided; high-level system requirements are established; decisions are made on
how functionality will be distributed across hardware, software, and people; and
the components that will make up the system are purchased.
2. Development During this stage, the system is developed. Development
processes include all of the activities involved in system development such as
requirements definition, system design, hardware and software engineering,
system integration, and testing. Operational processes are defined and the train-
ing courses for system users are designed.
3. Operation At this stage, the system is deployed, users are trained, and the sys-
tem is brought into use. The planned operational processes usually then have to
change to reflect the real working environment where the system is used. Over
time, the system evolves as new requirements are identified. Eventually, the sys-
tem declines in value and it is decommissioned and replaced.

These stages are not independent. Once the system is operational, new equipment
and software may have to be procured to replace obsolete system components, to
provide new functionality, or to cope with increased demand. Similarly, requests for
changes during operation require further system development.