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software testing and quality assurance
Software Engineering 10th Edition Ian Sommerville - Solutions
=+24.2. Explain how standards may be used to capture organizational wisdom about effective methods of software development. Suggest four types of knowledge that might be captured in organizational standards.
=+24.1. Define the terms quality assurance and quality control. List out the key points included in Humphrey’s outline structure for software management.
=+23.10. Is it ethical for a company to quote a low price for a software contract knowing that the requirements are ambiguous and that they can charge a high price for subsequent changes requested by the customer?
=+23.9. Some very large software projects involve writing millions of lines of code. Explain why the effort estimation models, such as COCOMO, might not work well when applied to very large systems.
=+Explain why this estimate should be adjusted to take project, personnel, product, and organizational factors into account. Suggest four factors that might have significant effects on the initial COCOMO estimate and propose possible values for these factors. Justify why you have included each
=+ The COCOMO method is used to estimate the effort required to develop this system, and an estimate of 26 person-months is computed. All cost driver multipliers were set to 1 when making this estimate.
=+fixed amount of memory (256 Mbytes). The machine communicates with a patient database system to obtain the details of the patient and, after treatment, automatically records the radiation dose delivered and other treatment details in the database.
=+23.8. A software manager is in charge of the development of a safety-critical software system, which is designed to control a radiotherapy machine to treat patients suffering from cancer.This system is embedded in the machine and must run on a special-purpose processor with a
=+23.7. The planning game is based on the notion of planning to implement the stories that represent the system requirements. Explain the potential problems with this approach when software has high performance or dependability requirements.
=+23.6. Figure 23.14 shows the task durations for software project activities. Assume that a serious, unanticipated setback occurs, and instead of taking 10 days, task T5 takes 40 days. Draw up new bar charts showing how the project might be reorganized.
=+23.5. Figure 23.14 sets out a number of tasks, their durations, and their dependencies. Draw a bar chart showing the project schedule.
=+23.4. What is algorithmic cost modeling? What problems does it suffer from when compared with other approaches to cost estimation?
=+23.3. Define project scheduling. What are the things to be considered while estimating schedules?
=+23.2. Explain why the process of project planning is iterative and why a plan must be continually reviewed during a software project.
=+23.1. Describe the factors that affect software pricing. Define the “pricing to win” approach in software pricing.
=+ What factors might be significant in your decision?
=+Discuss whether you should accept this demand from your manager or whether you should persuade your team to give their time to the organization rather than to their families.
=+22.10. Your manager asks you to deliver software to a schedule that you know can only be met by asking your project team to work unpaid overtime. All team members have young children.
=+22.9. Write a case study in the style used here to illustrate the importance of communications in a project team. Assume that some team members work remotely and that it is not possible to get the whole team together at short notice.
=+22.8. What qualities of a cohesive group’s members make the group robust? List out the key benefits of creating a cohesive group.
=+22.7. Explain why keeping all members of a group informed about progress and technical decisions in a project can improve group cohesiveness.
=+contractor has to pay. Suggest how the use of such contracts may increase the likelihood that product risks will arise.
=+22.6. Fixed-price contracts, where the contractor bids a fixed price to complete a system development, may be used to move project risk from client to contractor. If anything goes wrong, the
=+22.5. What is risk monitoring? How can risks be monitored? List a few examples of types of risks and their potential indicators.
=+22.4. In addition to the risks shown in Figure 22.1, identify at least six other possible risks that could arise in software projects.
=+The Mythical Man Month, as suggested in Further Reading.)
=+22.3. Using reported instances of project problems in the literature, list management difficulties and errors that occurred in these failed programming projects. (I suggest that you start with
=+22.2. Explain how company size and software size are factors that affect software project management.
=+22.1. Explain why the intangibility of software systems poses special problems for software project management.
=+ Discuss the ethics of both introducing a logging system and doing so without telling system users.
=+14.10. A senior manager in a company is concerned about insider attacks from disaffected staff on the company’s IT assets. As part of a resilience improvement program, she proposes that a logging system and data analysis software be introduced to capture and analyze all employee actions but
=+Draw up a test plan for this system that sets out how you could test the ability of the Mentcare system to recognize, resist, and recover from these events.
=+14.9. In Figure 14.11, I suggested a number of adverse events that could affect the Mentcare system.
=+14.8. In Section 13.4.2, (1) an unauthorized user places malicious orders to move prices and (2) an intrusion corrupts the database of transactions that have taken place. For each of these cyberattacks, identify resistance, recognition, and recovery strategies that might be used.
=+14.7. Suggest how the approach to resilience engineering that I proposed in Figure 14.9 could be used in conjunction with an agile development process for the software in the system. What problems might arise in using agile development for systems where resilience is important?
=+of process inflexibility, illustrate your answer with examples from your experience.
=+14.6. Explain why process inflexibility can inhibit the ability of a sociotechnical system to resist and recover from adverse events such as cyberattacks and software failure. If you have experience
=+14.5. What is survivable systems analysis and what are the key activities in each of the four stages involved in it as shown in Figure 14.8?
=+is likely to adversely affect the resilience of the organization.
=+14.4. A hospital proposes to introduce a policy that any member of clinical staff (doctors or nurses)who takes or authorizes actions that leads to a patient being injured will be subject to criminal charges. Explain why this is a bad idea, which is unlikely to improve patient safety, and why it
=+14.3. Describe the ways in which human error can be viewed according to Reason (Reason, 2000)and the strategies that can be used to increase resilience according to the Swiss cheese model (Figure 14.6).
=+14.2. What are the types of threats that have to be considered in resilience planning? Provide examples of the controls that organizations should put in place to counter those threats.
=+14.1. Explain how the complementary strategies of resistance, recognition, recovery, and reinstatement may be used to provide system resilience.
=+13.10. The Mentcare system has to be secure against attacks that might reveal confidential patient information. Suggest three possible attacks against this system that might occur. Using this information, extend the checklist in Figure 13.17 to guide testers of the Mentcare system.
=+13.9. Suggest how you would go about validating a password protection system for an application that you have developed. Explain the function of any tools that you think may be useful.
=+13.8. Explain why it is important when writing secure systems to validate all user inputs to check that these have the expected format.
=+Figure 13.14, suggest two further plausible attacks on the system and propose possible strategies that could counter these attacks.
=+13.7. For the equity trading system discussed in Section 13.4.2, whose architecture is shown in
=+13.6. Explain why it is important to log user actions in the development of secure systems.
=+13.5. Explain, using an analogy drawn from a non-software engineering context, why a layered approach to asset protection should be used.
=+that implement the proposed controls.
=+13.4. Extend the table in Figure 13.7 to identify two further threats to the Mentcare system, along with associated controls. Use these as a basis for generating software security requirements
=+13.3. Explain why security is considered a more challenging problem than safety in a system.
=+13.2. For the Mentcare system, suggest an example of an asset, an exposure, a vulnerability, an attack, a threat, and a control, in addition to those discussed in this chapter.
=+13.1. Describe the security dimensions and security levels that have to be considered in secure systems engineering.
=+12.10. Should software engineers working on the specification and development of safety-related systems be professionally certified or licensed in some way? Explain your reasoning.
=+(iii) An authorized operator is identified by the input of an authorized door entry code.The code shown in Figure 12.15 controls the door-locking mechanism. Note that the safe state is that entry should not be permitted. Using the approach discussed in this chapter, develop a safety argument for
=+(ii) If the radiation level in a room is below a specified value, an authorized operator may open the door.
=+(i) If remotely controlled radiation shields are in place within a room, an authorized operator may open the door.
=+12.9. The door lock control mechanism in a nuclear waste storage facility is designed for safe operation. It ensures that entry to the storeroom is only permitted when radiation shields are in place or when the radiation level in the room falls below some given value (dangerLevel).So:
=+12.8. List four types of systems that may require software safety cases, explaining why safety cases are required.
=+12.7. Explain why using model checking is sometimes a more cost-effective approach to verification than verifying a program’s correctness against a formal specification.
=+12.6. Explain when it may be cost-effective to use formal specification and verification in the development of safety-critical software systems. Why do you think that some critical systems engineers are against the use of formal methods?
=+on-board software on the train before it enters the track segment, propose five possible functional system requirements for the onboard software that may be generated from the system safety requirements.
=+The train shall not enter a segment of track that is signaled with a red light.The train shall not exceed the specified speed limit for a section of track.Assuming that the signal status and the speed limit for the track segment are transmitted to
=+12.5. A train protection system automatically applies the brakes of a train if the speed limit for a segment of track is exceeded, or if the train enters a track segment that is currently signaled with a red light (i.e., the segment should not be entered). There are two critical-safety
=+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 defense is likely to reduce the risk associated with the hazard.
=+■ The minimum and maximum speeds of the roller coaster as it moves along the various segments of the ride to prevent derailing, given the number of people riding the roller coaster.
=+12.4. A safety-critical software system for managing roller coasters controls two main components:■ The lock and release of the roller coaster harness which is supposed to keep riders in place as the coaster performs sharp and sudden moves. The roller coaster could not move with any unlocked
=+12.3. 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
=+12.2. A software system is to be deployed for a company that has extremely high safety standards and allows for almost no risks, not even minor injuries. How will this affect the look of the risk triangle in Figure 12.3?
=+12.1. Identify six consumer products that are likely to be controlled by safety-critical software systems.
=+warranties in the same way that consumer goods manufacturers must guarantee their products?
=+to software failures? Should they be liable for compensating users for losses that are caused by the failure of their software? Should they be required by law to offer software
=+11.10. Software failures can cause considerable inconvenience to users of the software. Is it ethical for companies to release software that they know includes faults that could lead
=+ 11.9. Explain how programming language support of exception handling can contribute to the reliability of software systems.
=+11.8. Explain why all the versions in a system designed around software diversity may fail in a similar way.
=+ 11.7. It has been suggested that the control software for a radiation therapy machine, used to treat patients with cancer, should be implemented using N-version programming. Comment on whether or not you think this is a good suggestion.
=+ 11.6. You are responsible for the design of a communications switch that has to provide 24/7 availability but that is not safety-critical. Giving reasons for your answer, suggest an architectural style that might be used for this system.
=+ 11.5. Suggest circumstances where it is appropriate to use a fault-tolerant architecture when implementing a software-based control system and explain why this approach is required.
=+ 11.4. What is the common characteristic of all architectural styles that are geared to supporting software fault tolerance?
=+11.3. Imagine that a network operations center monitors and controls the national telecommunications network of a country. This includes controlling and monitoring the operational status of switching and transmission equipment and keeping track of nationwide equipment inventories. The center
=+ 11.2. Suggest appropriate reliability metrics for the classes of software system below. 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
=+expressed in terms of a very small number of failures over the total lifetime of a system.
=+11.1. Explain why it is practically impossible to validate reliability specifications when these are
=+ Discuss whether or not you think this is true and the desirability of regulators imposing their views on what methods should be used.
=+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.
=+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.
=+10.9. 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
=+10.8. Give two reasons why different versions of a system based on software diversity may fail in a similar way.
=+10.7. Give two examples of diverse, redundant activities that might be incorporated into dependable processes.
=+10.6. Explain why it is reasonable to assume that the use of dependable processes will lead to the creation of dependable software.
=+10.5. Explain the difference between redundancy and diversity.
=+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.
=+10.3. 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.
=+10.2. Explain with an example why resilience to cyber attacks is a very important characteristic of system dependability.
=+10.1. Suggest six reasons why software dependability is important in most sociotechnical systems.
=+9.10. Do software engineers have a professional responsibility to develop code that can be easily maintained even if their employer does not explicitly request it?
=+ 9.9. Explain the differences between software reengineering and refactoring?
=+ 9.8. Briefly describe the three main types of software maintenance. Why is it sometimes difficult to distinguish between them?
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