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Chapter 11 Exercises 307

EXERCISES

11.1. Suggest six reasons why software dependability is important in most sociotechnical
systems.
11.2. What are the most important dimensions of system dependability?
11.3. Why do the costs of assuring dependability increase exponentially as the reliability
requirement increases?
11.4. Giving reasons for your answer, suggest which dependability attributes are likely to be most
critical for the following systems:

An Internet server provided by an ISP with thousands of customers
A computer-controlled scalpel used in keyhole surgery
A directional control system used in a satellite launch vehicle

An Internet-based personal finance management system
11.5. Identify six consumer products that are likely to be controlled by safety-critical software
systems.

11.6. Reliability and safety are related but distinct dependability attributes. Describe the most
important distinction between these attributes and explain why it is possible for a reliable
system to be unsafe and vice versa.

11.7. In a medical system that is designed to deliver radiation to treat tumors, suggest one hazard
that may arise and propose one software feature that may be used to ensure that the
identified hazard does not result in an accident.
11.8. In computer security terms, explain the differences between an attack and a threat.
11.9. Using the MHC-PMS as an example, identify three threats to this system (in addition to the
threat shown in Figure 11.8). Suggest controls that might be put in place to reduce the
chances of a successful attack based on these threats.

11.10. As an expert in computer security, you have been approached by an organization that
campaigns for the rights of torture victims and have been asked to help the organization
gain unauthorized access to the computer systems of an American company. This will help
them confirm or deny that this company is selling equipment that is used directly in the
torture of political prisoners. Discuss the ethical dilemmas that this request raises and how
you would react to this request.