Sommerville-Software-Engineering-10ed

292 Chapter 10 ■ Dependable systems
Society
Organization
Business processes
Systems
engineering
Application system
Communications and data management
Software
engineering
Figure 10.3 The
sociotechnical
systems stack
Operating system
Equipment
These broader systems are called sociotechnical systems. They include nontechnical
elements such as people, processes, and regulations, as well as technical
components such as computers, software, and other equipment. System dependability
is influenced by all of the elements in a sociotechnical system—hardware, software,
people, and organizations.
Sociotechnical systems are so complex that it is impossible to understand them as
a whole. Rather, you have to view them as layers, as shown in Figure 10.3. These
layers make up the sociotechnical systems stack:
1. The equipment layer is composed of hardware devices, some of which may be
computers.
2. The operating system layer interacts with the hardware and provides a set of
common facilities for higher software layers in the system.
3. The communications and data management layer extends the operating system
facilities and provides an interface that allows interaction with more extensive
functionality, such as access to remote systems and access to a system database.
This is sometimes called middleware, as it is in between the application and the
operating system.
4. The application layer delivers the application-specific functionality that is
required. There may be many different application programs in this layer.
5. The business process layer includes the organizational business processes,
which make use of the software system.
6. The organizational layer includes higher-level strategic processes as well as
business rules, policies, and norms that should be followed when using the
system.
7. The social layer refers to the laws and regulations of society that govern the
operation of the system.