- ✓An SDLC provides a structured framework of phases that guide a software project from initial concept through to deployment and maintenance.
- ✓The Waterfall model is linear and sequential, completing each phase fully before moving to the next, which suits stable, well-understood requirements.
- ✓The Spiral model combines iterative development with risk analysis, making it appropriate for large, high-risk projects.
- ✓Rapid Application Development prioritises speed of delivery through prototyping and close user involvement throughout the process.
- ✓No single SDLC model is universally superior; the right choice depends on the size, complexity, and nature of the specific project.
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Start learning →Alex: We're starting Unit 7 today: Software Development Lifecycles. Sam, what's the purpose of having a defined lifecycle for software development?
Sam: Software development without a structured approach is risky. Without a lifecycle framework, projects tend to lack clear phases, deliverables, and checkpoints. People jump straight into coding without fully understanding requirements, testing gets rushed or skipped, and projects frequently fail to deliver on time, within budget, or to the quality required. An SDLC provides a shared framework that guides the team from initial idea through to a delivered, operational product.
Alex: What are the main SDLC models we need to know?
Sam: The key ones are Waterfall, Spiral, RAD, and the various Agile frameworks. Each represents a different philosophy about how software development should be structured, with different trade-offs in terms of predictability, flexibility, and risk.
Alex: Let's start with Waterfall.
Sam: Waterfall is the oldest and most straightforward model. It's linear and sequential: you complete each phase fully before moving to the next. The typical phases are requirements, design, implementation, testing, deployment, and maintenance. Each phase produces documented deliverables that are reviewed before the next phase begins. It's called Waterfall because progress flows downward like water over a series of steps.
Alex: What are its strengths and weaknesses?
Sam: Waterfall is strong on predictability and documentation. When requirements are stable and well-understood upfront, and when the technology is mature, Waterfall can deliver reliable results. Its weakness is inflexibility: if requirements change after the design phase, making those changes is costly and disruptive. Real-world projects rarely have perfectly stable requirements, which is why Waterfall became increasingly criticised from the 1990s onwards.
Alex: What about Spiral?
Sam: The Spiral model was developed by Barry Boehm as an alternative for high-risk projects. It organises development into a series of cycles, or spirals, where each cycle goes through four phases: determine objectives and constraints, evaluate alternatives and identify risks, develop and test, and plan the next iteration. The explicit focus on risk analysis at each cycle makes it particularly appropriate for large, complex projects where uncertainty is high.
Alex: And RAD?
Sam: Rapid Application Development emphasises speed by replacing extensive upfront planning with rapid prototyping and iterative development. Requirements and design emerge through the prototyping process as users interact with working software and provide feedback. It's particularly effective when time to market is critical and when users can be actively involved in development. The trade-off is that it can produce systems that lack the architectural rigour of more carefully planned approaches.
Alex: And all of these set the context for understanding Agile, which we cover next?
Sam: Exactly. Agile grew partly as a reaction to the perceived inflexibility of plan-driven models like Waterfall, drawing on ideas from Spiral and RAD but formalising them into frameworks like Scrum and Kanban. Understanding the historical context makes Agile's principles much more comprehensible.
Alex: Thanks Sam. In the next lesson we do a deep dive into Waterfall versus Agile.