Sommerville-Software-Engineering-10ed

304 Chapter 10 ■ Dependable systems
Exercises
10.1. Suggest six reasons why software dependability is important in most sociotechnical systems.
10.2. Explain with an example why resilience to cyber attacks is a very important characteristic of
system dependability.
10.3. Using an example, explain why it is important when developing dependable systems to consider
these as sociotechnical systems and not simply as technical software and hardware systems.
10.4. Give two examples of government functions that are supported by complex sociotechnical
systems and explain why, in the foreseeable future, these functions cannot be completely
automated.
10.5. Explain the difference between redundancy and diversity.
10.6. Explain why it is reasonable to assume that the use of dependable processes will lead to the
creation of dependable software.
10.7. Give two examples of diverse, redundant activities that might be incorporated into dependable
processes.
10.8. Give two reasons why different versions of a system based on software diversity may fail in
a similar way.
10.9. You are an engineer in charge of the development of a small, safety-critical train control
system, which must be demonstrably safe and secure. You suggest that formal methods
should be used in the development of this system, but your manager is skeptical of this
approach. Write a report highlighting the benefits of formal methods and presenting a
case for their use in this project.
10.10. It has been suggested that the need for regulation inhibits innovation and that regulators
force the use of older methods of systems development that have been used on other
systems. Discuss whether or not you think this is true and the desirability of regulators
imposing their views on what methods should be used.
References
Abrial, J. R. 2009. “Faultless Systems: Yes We Can.” IEEE Computer 42 (9): 30–36. doi:10.1109/
MC.2009.283.
. 2010. Modeling in Event-B: System and Software Engineering. Cambridge, UK: Cambridge
University Press.
Avizienis, A., J. C. Laprie, B. Randell, and C. Landwehr. 2004. “Basic Concepts and Taxonomy of
Dependable and Secure Computing.” IEEE Trans. on Dependable and Secure Computing 1 (1): 11–33.
doi:10.1109/TDSC.2004.2.
Badeau, F., and A. Amelot. 2005. “Using B as a High Level Programming Language in an Industrial
Project: Roissy VAL.” In Proc. ZB 2005: Formal Specification and Development in Z and B. Guildford,
UK: Springer. doi:10.1007/11415787_20.