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278 Chapter 10 Sociotechnical systems

Requirements System
Development Deployment

System System
Design Testing

Subsystem System
Figure 10.7 Systems Engineering Integration
development

10.4 System development

The goals of the system development process are to develop or acquire all of the
components of a system and then to integrate these components to create the final
system. The requirements are the bridge between the procurement and the develop-
ment processes. During procurement, business and high-level functional and non-
functional system requirements are defined. You can think of this as the start of
development, hence the overlapping processes shown in Figure 10.4. Once contracts
for the system components have been agreed, more detailed requirements engineer-
ing then takes place.
Figure 10.7 is a model of the systems development process. This systems engi-
neering process was an important influence on the ‘waterfall’ model of the software
process that I discussed in Chapter 2. Although it is now accepted that the ‘waterfall’
model is not usually appropriate for software development, most systems develop-
ment processes are plan-driven processes that still follow this model.
Plan-driven processes are used in systems engineering because different parts of
the system are being developed at the same time. For systems that include hardware
and other equipment, changes during development can be very expensive or, some-
times, practically impossible. It is essential therefore, that the system requirements
are fully understood before hardware development or building work begins.
Reworking the system design to solve hardware problems is rarely possible. For this
reason, more and more system functionality is being assigned to the system soft-
ware. This allows some changes to be made during system development, in response
to new system requirements that inevitably arise.
One of the most confusing aspects of systems engineering is that companies use
different terminology for each stage of the process. The process structure also varies.
Sometimes, requirements engineering is part of the development process and some-
times it is a separate activity. However, there are essentially six fundamental activities
in systems development:

1. Requirements development The high-level and business requirements identified
during the procurement process have to be developed in more detail.
Requirements may have to be allocated to hardware, software, or processes and
prioritized for implementation.