L03: Software Lifecycle

Question 1

What factors do we consider when choosing a software engineering process?

Answer 1

Choice of software process typically depends on:
- Characteristics of system being developed
- Customer requirements
- Skills and experience of development team
- Organisational culture and practices

An appropriate software process should be chosen for a system based on the project and its context

Question 2

What are some examples of software lifecycle/process models?

Answer 2

• Prescriptive models (such as waterfall)
• Iterative and incremental development (such as agile)
• Integration and configuration

Question 3

What is a software lifecycle/process model?

Answer 3

A software process model or lifecycle is an abstract
representation of software processes

• What activity should be done next
• How long it should last
• Process determines activities and how they are structured
• As well as outcomes, role of stakeholders involved and pre- and post-conditions of activities

Question 4

What is a lifecycle?

Answer 4

Oxford English Dictionary
“In extended use:
a course or evolution from a beginning, through
development and productivity, to decay or ending.”

Question 5

What are the stages of a software lifecycle?

Answer 5

• Inception
• Feasibility
• Commissioning
• Development
• Acceptance testing
• Deployment and operation
• Maintenance and evolution
• Phase-out

Question 6

What is the waterfall model?

Answer 6

Requirements specification
-> Design
-> Implementation
-> Validation
-> Operation
-> Maintenance

Question 7

What happens in a modified waterfall model?

Answer 7

After the maintenance phase, the process goes back to the requirements specification phase

Question 8

What are the pros of the waterfall model?

Answer 8

Can be used when
- Requirements are well understood
- Requirements are unlikely to change radically during development

Possibly suitable for
- Embedded systems
- Critical systems
- Collaborative development scenarios for large engineering projects

Question 9

What are the cons of the waterfall model?

Answer 9

• Plan-driven
• Lacks flexibility as you cannot go through the phase in any other order

Question 10

What is the spiral model?

Answer 10

Incremental but systematic
- Risk-driven software process framework
- Changes are results of project risks
- Process and product are determined by risks
- Aims to lower development costs by early elimination of
alternatives that are not viable
Each loop in the spiral
- A phase of the process

Question 11

What are the 4 sectors in each loop of the spiral model?

Answer 11

• Objective setting
• Risk assessment and reduction
• Development and validation
• Planning for next loop

Question 12

What is iterative and incremental development (IID)?

Answer 12

Initial release of software, followed by refinements
- Increments incorporating feedback from stakeholders
- Plan-driven or agile or a mix of both
- Basis for current development methods

Question 13

What are the pros of IID?

Answer 13

• Quicker delivery and deployment of useful software to customers
• Earlier feedback from customers on work completed
• Reduced cost of accommodating changes to customer
  requirements
• Earlier identification of risks and mitigations

Question 14

What are the cons of IID?

Answer 14

• Lack of visible process and complete documentation
• Degrading system structure as more increments are added
• Challenges in identifying common concerns and utilities that apply across the system
• Conflicts with procurement models of organisations without complete specification at the start

Question 15

What is the integration and configuration model?

Answer 15

Software reuse is common in projects
- Reuse-oriented approaches
- Reusable software components
Examples
- General-purpose stand-alone systems that can be
configured
- Web services satisfying service standards and can be
remotely invoked
- An integrating framework for composing components

Question 16

What are the stages in reuse-oriented software engineering?

Answer 16

Requirement specification
-> Requirement refinement

If there is an application system available to refactor, the application system is configured

If there are components available (but not the full system), they are developed and adapted to be integrated in the system