Exam Preparation

Internal Attributes
These can be measured by examining the object on its own, separate from its behaviour.

External Attributes
These can be measured only with respect to how the object relates to its environment.

The system should be fast – a non-quantifiable requirement.

This cannot be tested how do we know if it succeeds or not, can give rise to debate later on if the user complains the system is not fast enough and it does not give the developer guidance. It is of little use.

Measurements will show if techniques really improve the software, as well as how process quality affects product quality.

We need to know how the quality we build in can affect the product’s use after delivery and if the investment of time and resources to assure high quality reap higher profits or larger market share.

Concerns ‘fitness for use’.

The user view is concrete, grounded in product characteristics that meet
the user’s needs.

This view of quality evaluates the product in a task context and can thus
be a highly personalised view.

• Reliability
• Performance
• Usability.

Whereas the user view examines the product from without, a product view of quality looks inside, considering the product’s inherent characteristics. Relates to attributes of the software.

This approach is frequently adopted by software-metrics advocates, who assume that measuring and controlling internal product properties (internal quality indicators) will result in improved external product behaviour (quality in use).

Developer’s view will be determined by technical properties of the interface:

• use of windows, buttons, scrollbars, pop-up menus etc.
• User friendliness is seen from the inside.

The user is concerned with getting the job done in the most effective way, user interfaces should be friendly and they should support their work.

• Time needed to learn the system (learnability)
• Time to perform tasks when trained, or errors made when working at normal speed (operability)
• Retention of system knowledge over time (memorability)
• Age or required experience (understandability)

The measure is quite useful for developers but is almost useless for users or potential purchasers. For developers who measure both LOC and faults found (in the code) in a consistent manner, the measure will indicate:

• Broad differences in quality among different modules, systems and teams.
• Trends that can aid quality-control efforts;
• Potential trouble spots in the system;
• When the developers have reached the point of diminishing returns on testing.

However the measure is of limited usefulness to the user, as it:

• Gives no real indicator of reliability – a system with a large number of defects may not fail;
• Gives no real indicator of usability;
• Gives no real indicator of the severity of the faults;
• Cannot be used to compare products from different producers; LOC may not be counted consistently and faults may be classified differently;
• May say more about the testing process than the quality of code;
• Invite abuse by programmers who may increase the length of a program to decrease defect density and thus appear to produce higher quality code;
• Is irrelevant for assessing quality before coding has begun;
• Cannot be compared with products whose size is not measured in LOC;
• Does not take into account reused code.

Removing 50% of faults tells nothing about improvements in reliability, the type of faults need to be known. A systems with one fault will have poor reliability if the fault is serious, a system with many faults may have high reliability if the faults are minor.

a) What are the fundamental activities that are common to all software process? (2 Marks)

• Specification
  defining what the system should do;
• Design and implementation
  defining the organization of the system and implementing the system;
• Validation
  checking that it does what the customer wants;
• Evolution
  changing the system in response to changing customer needs.

b) Change is inevitable in all large software projects, what are the main sources of change? (2 Marks)

• Business changes lead to new and changed system requirements.
• New technologies open up new possibilities for improving implementations.
• Management priorities change

c) Change leads to rework, how can the cost of rework be reduced? (4 Marks)

• Change avoidance, where the software process includes activities that can anticipate possible changes before significant rework is required.
• Change tolerance, where the process is designed so that changes can be accommodated at relatively low cost.

d) For incremental development: (8 Marks)

i) Outline the advantages and disadvantages.

Advantages

• Customer value can be delivered with each increment.
• Accelerated delivery of customer services.
• Highest priority services are delivered first and later increments are integrated with them, thus undergoing the most testing – less failures in the most important part of the system.
• Early increments act as a prototype to help elicit requirements for later increments.
• Lower risk of project failure

Disadvantages

• Increments should be small and yet deliver some functionality. It may be difficult to map functionality onto increments of the right size.
• Some systems require a set of basic facilities used by different parts of the system. It can be hard to identify common facilities.
• Specification develops with the software.

ii) Describe the sort of project that would be an ideal application. 

Answer
Facebook like project (Expand answer)

e) Explain why iterations usually are limited in the waterfall model (2 Marks)

An iterative process is typified by repeated execution of the waterfall phases in whole or part. An iterative process is incremental if each iteration is relatively small and delivers a subset of the final product’s functionality and features.

f) Explain the difference between iterative and incremental development. (2 Marks)

• Iterative
  The essence of an iterative process is that the specification is developed in conjunction with the software.
• Incremental
  Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.

g) Give an evaluation of spiral development. (6 Marks)

• Objective setting
  Specific objectives for the phase are identified.
• Risk assessment and reduction
  Risks are assessed and activities put in place to reduce the key risks. Evaluation of project and process alternatives for achieving the objectives.
• Development and validation
  A development model for the system is chosen which can be any of the generic models.
• Planning
  The project is reviewed and the next phase of the spiral is planned.

Spiral Model Advantages

• Risks are managed early and throughout the process – they are reduced before they become problematic.
• Software evolves as the project progresses – it is a realistic approach to the development of large-scale software. Errors and unattractive alternatives are eliminated early.
• Planning is built into the process – each cycle contains a planning step to help monitor and keep a project on track

Spiral Model Disadvantages

• Complicated to use requires risk assessment expertise.
• Can only be used for large-scale, in-house development due to possible contractual problems.
• Maybe overkill for small projects – does not make sense if the cost of risk analysis is a major part of the overall cost.

a) Compare and contrast the following life-cycle models:
Waterfall Evolutionary development
Incremental development (14 Marks)

b) What are the characteristics of an agile approach to modern software development? (3 Marks)

Agile – Not in Exam

c) What are the key values proposed by the “Manifesto for Agile Software Development”? (4 Marks)

Agile – Not in Exam

d) What are the problems associated with an agile approach? (4 Marks)

Agile – Not in Exam

a) What is a software process model? (3 Marks)

A software process model describes the sequence of phases for the entire lifetime of a product. it is sometimes called Product Life Cycle.

There are 3 main phases

• Concept
• Implementation
• Maintenance

b) Give an evaluation of the waterfall model of the software process. Is it an accurate reflection of software development activities? (10 Marks)

One of the oldest software process models. Despite its many weaknesses, it is still widely used and is the basis for other more effective processes.

• Separate and distinct phases of specifications and development executed is a sequential manner.
• The output of one phase is the input for the next, a phase is not started until the previous phase is complete.
• Milestones are reached if the appropriate documentation is delivered.
• Documentation-driven, planning driven, heavyweight.
• Much planning upfront.
• Testing is performed at the end of the development.

c) Compare and contrast evolutionary and throwaway prototyping, suggest an appropriate project for each. Explain your reasoning (10 Marks)

• Evolutionary prototyping
  – An approach to system development where an initial prototype is produced and refined through a number of stages to the final system.

Analysis, design and implementation are performed concurrently and the three phases are
performed repeatedly until the system is complete.

The first prototype is the part of the system which has the best know requirements and this is shown to the user for feedback. This feedback is incorporated to produce a second prototype and the process continues until the system is complete.

Spans the entire SDLC.

• Throw-away prototyping
  – A prototype which is usually a practical implementation of the system is produced to
  help discover requirements problems and then discarded. The system is then developed using some other development process.

A thorough analysis is performed, any requirement or technical issue that the user does not understand will be examined by building a design prototype.

Users are shown the prototype and using user feedback the designers generate another prototype and again show it to the users.

The model-critique-refine process continues until the prototype is approved.

Once approved, the prototype is discarded and its design specifications are used to implement the production system with other tools and techniques.

Is used only during the design phase of the SDLC.

d) Can one process model be used for all types of software development? Explain your reasoning. (2 Marks)

Answer
Waterfall

a) Explain the differences between a heavy (plan driven) and a light (agile) approach to software development. (5 Marks)

Answer
Waterfall v Agile

b) For incremental development:

i) Outline the advantages and disadvantages.

Advantages

• Customer value can be delivered with each increment.
• Accelerated delivery of customer services.
• Highest priority services are delivered first and later increments are integrated with them, thus undergoing the most testing – less failures in the most important part of the system.
• Early increments act as a prototype to help elicit requirements for later increments.
• Lower risk of project failure

Disadvantages

• Increments should be small and yet deliver some functionality. It may be difficult to map functionality onto increments of the right size.
• Some systems require a set of basic facilities used by different parts of the system. It can be hard to identify common facilities.
• Specification develops with the software.

ii) Describe the sort of project that would be an ideal application. Now describe the type of situation where the model may lead to difficulties. (10 Marks)

Answer
Facebook like project (Expand answer)

c) Explain the difference between iterative and incremental development. (2 Marks)

• Iterative
  The essence of an iterative process is that the specification is developed in conjunction with the software.
• Incremental
  Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.

d) What are the key values (trade-offs) proposed by the “Manifesto for Agile Software development”? (4 Marks)

Agile – Not in Exam

e) What are the pros and cons of each value listed in the Agile Manifesto? (4 Marks)

Agile – Not in Exam

a) What is a software process model? (3 Marks)

A software process model describes the sequence of phases for the entire lifetime of a product. it is sometimes called Product Life Cycle.

There are 3 main phases

• Concept
• Implementation
• Maintenance

b) Compare and contrast the following life-cycle models:

Waterfall Evolutionary development Incremental development (14 Marks)

c) Explain the differences between a heavy (plan driven) and a light (agile) approach to software development. (5 Marks)

Answer
Waterfall v Agile

d) When would you recommend against the use of an agile method for developing a software system? (3 Marks)

Answer
Governmental / Military or Law (Document Heavy)

a) Do you consider software measurement to be important? Explain your reasoning (4 Marks)

Measurement is important for three basic activities :

• Measures help to understand what is happening during development and maintenance. We can assess the current situation and set goals for the future.
• Measurements allow control over what is happening on projects.
• Measurements encourage the improvement of processes and products.

b) Explain the difference between an internal and external attribute? (2 Marks)

Internal Attributes
These can be measured by examining the object on its own, separate from its behaviour.

External Attributes
These can be measured only with respect to how the object relates to its environment.

c) Explain the terms software fault and software failure, what is the relationship between them? (3 Marks)

Fault : An incorrect step, process, or data definition in a computer program which causes the program to perform in an unintended or unanticipated manner. It is an inherent weakness of the design or implementation which might result in a failure.

Failure: The inability of a system or component to perform its required functions within specified performance requirements

d) If half of all faults in an operational software system are removed what corresponding improvements would be expected in the reliability of the system? (3 Marks)

Removing 50% of faults tells nothing about improvements in reliability, the type of faults need to be known. A systems with one fault will have poor reliability if the fault is serious, a system with many faults may have high reliability if the faults are minor.

e) Why is reliability an external attribute of software? Suggest three internal attributes that could affect reliability. (5 Marks)

it is how the object (software) relates to its environment.

• Length – physical size.
• Functionality – the functions supplied by the product to the user.
• Complexity – of the underlying problem the software is solving.

f) You have been asked to improve the quality of the software products your company produces by improving reliability. Suggest four metrics which could be collected for this purpose and describe an appropriate system for each. (8 Marks)

NOT Answered

a) What are the stages of process improvement? (7 Marks)
Slide 5

• Measure where you currently are :: There is a link between the quality of the development process and the quality of the products developed using the process.

• Stabilize the current process :: Process improvement: Understanding existing processes and introducing process changes to improve product quality, reduce costs or accelerate schedules.

• Improve identified targets :: Most process improvement work so far has focused on defect reduction. This reflects the increasing attention paid by industry to quality.

b) What is process capability assessment, what is its purpose? (2 Marks)
Slide 20

• Intended as a means to assess the extent to which an organisation’s processes follow best practice.

• By providing a means for assessment, it is possible to identify areas of weakness for process improvement.

• The SEI work has been most influential.

c) The Capability Maturity Model (CMMI) is the most influential model for this purpose, briefly describe what this model is. (2 Marks)

CMMI is a world-class performance improvement model for competitive organizations that want to achieve high-performance operations. Proven effective in organizations and governments globally over the last 25 years, CMMI consists of collected best practices designed to promote the behaviors that lead to improved performance in any organization.

d) In the context of CMMI explain each of the following terms and the relationship between them:

• Key process area
KPAs identify the issues that must be addressed to achieve a given maturity level.

• Goal.
A specific goal describes the unique characteristics that must be present to satisfy the process area.

• Practice. (6 Marks)
A specific practice is the description of an activity that is considered important in achieving the associated specific goal.

d) Explain the staged CMMI, when should it be used? (4 Marks)

The staged representation offers a systematic, structured way to approach model-based process improvement one stage at a time.
If you do not know where to start and which processes to choose to improve, the staged representation is a good choice.

e) Are CMMI investments beneficial? (4 Marks)

Organisations involved show substantial improvements in :
• Productivity.
• Cycle time.
• Quality
• Business value ratio.

a) Explain why a high-quality software process should lead to high-quality software products. (5 Marks)

Process quality and product quality are closely related, the quality of a developed product is influenced by the quality of the production process A good process is usually required to produce a good product.

b) The CMMI (capability maturity model integration) is a framework for process improvement

• Explain how the model is used for this purpose. (6 Marks)

o The CMMI describes the key elements of an effective software process.
o The CMMI describes an evolutionary improvement path for software organisations from an ad hoc, immature process to a mature disciplined one.
o The CMMI covers practices for planning, engineering and managing software.

• Give two advantages and two disadvantages of the approach to process assessment and improvement which is embodied in this model. (4 Marks)

Advantages :: Productivity, Quality
DisAdvantages :: Cost, Time – 2years per level

c) The company you work for is planning to start a SPI (software process improvement) initiative and has set up a group to take responsibility for this effort. What advice would you give the group to improve their chances of success? (5 Marks)

Self-assessment – Team selection – Maturity questionnaire – Site visit – Presentation of findings

d) Measurement of process attributes is essential for process improvement, explain how GQM (goal question metric) can be used for this purpose. (5 Marks)

a) In your own words describe the levels of CMMI. (5 Marks)

b) Explain what is meant by the continuous and stage CMMI. Compare and contrast these two approaches. (13 Marks)

Continuous
Grants explicit freedom to select the order of improvement that best meets the organization’s business objectives and mitigates the organization’s areas of risk. Enables increased visibility of the capability achieved in each individual process area

Allows improvements of different processes to be performed at different rates. Reflects a newer approach that does not yet have the data to demonstrate its ties to return on investment.

Staged
Enables organizations to have a predefined and proven improvement path.

Focuses on a set of processes that provide an organization with a specific capability that is characterized by each maturity level.

Summarises process improvement results in a simple form—a single maturity level number.

Builds on a relatively long history of use that includes case studies and data that demonstrate return on investment.

c) Are CMM program investments beneficial? Where are the benefits to be realised? (7 Marks)

Organisations involved show substantial improvements in :
• Productivity.
• Cycle time.
• Quality
• Business value ratio.