Unit 1: Process models

Software is a set of programs plus documentation and data that make it work. Unlike hardware, it does not wear out, but it deteriorates as changes introduce errors, and it is largely custom-built. Categories: system software, application software, engineering/scientific software, embedded software, product-line software, web and mobile apps, and AI software. Software engineering (IEEE) is the application of a systematic, disciplined, quantifiable approach to the development, operation and maintenance of software.

The generic process framework has five activities: communication, planning, modelling, construction (coding and testing) and deployment, supported by umbrella activities such as project tracking, risk management, quality assurance and configuration management.

Phases of the Unified Process: inception, elaboration, construction, transition (and production).

• Advantages: simple, well-documented, easy to manage, suitable for stable requirements. Disadvantages: working software arrives late, changes are costly, risk is high, users see the product only at the end.

• Each increment follows a mini-waterfall; useful when staff are limited or an early market release is needed. RAD (rapid application development) is a high-speed incremental model using component reuse and short cycles (60–90 days).

• Advantages: clarifies unclear requirements, early user feedback, reduces risk of building the wrong product. Disadvantages: customers may mistake the prototype for the final system; quick-fix code may creep into the product.

• Proposed by Barry Boehm (1986); combines prototyping with the systematic waterfall approach and stresses risk analysis; each loop of the spiral is a phase.

• Advantages: risk-driven, suits large and high-risk projects, changes accommodated. Disadvantages: complex, costly, needs risk-assessment expertise, not for small projects.

• Activities (communication, modelling, construction) exist simultaneously, each in a state — inactive, under development, awaiting changes, under review, baselined or done. Events (such as a requirements change) trigger transitions. It reflects real projects in which several activities proceed in parallel, and suits client–server and web systems.

• A use-case driven, architecture-centric, iterative and incremental process created by Jacobson, Booch and Rumbaugh, using UML.

• Work products: vision document, use-case model, analysis and design models, software architecture description, test cases, deployment plan.

• Both were developed by Watts Humphrey at the SEI.

Agility is the ability to respond to change quickly. The Agile Manifesto values individuals and interactions over processes and tools, working software over comprehensive documentation, customer collaboration over contract negotiation, and responding to change over following a plan.

• Extreme Programming (XP): user stories, small releases, pair programming, test-first development, continuous integration, refactoring and simple design.
• Scrum: work is done in sprints (usually 2–4 weeks). Roles: Product Owner, Scrum Master, Development Team. Artefacts: product backlog, sprint backlog, increment. Events: sprint planning, daily stand-up, sprint review and retrospective.