Problem 2
In the insulin pump system, the user has to change the needle and insulin supply at regular intervals and may also change the maximum single dose and the maximum daily dose that may be administered. Suggest three user errors that might occur and propose safety requirements that would avoid these errors resulting in an accident.
Problem 3
A safety-critical software system for treating cancer patients has two principal components: A radiation therapy machine that delivers controlled doses of radiation to tumour sites. This machine is controlled by an embedded software system. A treatment database that includes details of the treatment given to each patient. Treatment requirements are entered in this database and are automatically downloaded to the radiation therapy machine. Identify three hazards that may arise in this system. For each hazard, suggest a defensive requirement that will reduce the probability that these hazards will result in an accident. Explain why your suggested defence is likely to reduce the risk associated with the hazard.
Problem 4
Describe three important differences between the processes of safety specification and security specification. 9.5 S
Problem 6
What is the fundamental difference between hardware and software failures? Given this difference, explain why hardware reliability metrics are often inappropriate for measuring software reliability.
Problem 7
Explain why it is practically impossible to validate reliability specifications when these are expressed in terms of a very small number of failures over the total lifetime of a system.
Problem 8
Suggest appropriate reliability metrics for the following classes of software system. Give reasons for your choice of metric. Predict the usage of these systems and suggest appropriate values for the reliability metrics: A system that monitors patients in a hospital intensive care unit A word processor An automated vending machine control system A system to control braking in a car A system to control a refrigeration unit A management report generator.
Problem 11
Should software engineers working on the specification and development of safety-related systems be professionally certified in some way? Explain your reasoning.
Problem 12
As an expert in computer security, you have been approached by an organisation that campaigns for the rights of torture victims and have been asked to help them gain unauthorised access to the computer systems of a British company. This will help them confirm or deny that this company is selling equipment used directly in the torture of political prisoners. Discuss the ethical dilemmas that this request raises and how you would react to this request.
