System Development Life Cycle

What is SDLC?

The System Development Life Cycle (SDLC) is a structured sequence of phases used to plan, build, deploy, and retire an information system. It provides a roadmap so that no critical activity is forgotten.

Phases of the SDLC

A classical SDLC has five (sometimes seven) phases:

1. Planning / Preliminary Investigation — identify the business problem, set objectives, perform feasibility.
2. Systems Analysis — gather requirements, model the current system, specify the new system.
3. Systems Design — design architecture, database, user interface, and programs.
4. Implementation — code, test, install, and train users.
5. Maintenance — fix bugs, add features, adapt to changes for as long as the system is in use.

Planning Phase

Outputs of the planning phase include a project charter, feasibility study, and initial budget. A feasibility study evaluates four aspects: technical, economic, operational, and schedule feasibility.

Analysis Phase

Analysts interview users, observe current operations, read existing documents, and run questionnaires to collect requirements. Outputs are a requirements specification, data flow diagrams, use cases, and an E-R model.

Design Phase

The design phase converts requirements into specifications. It produces architecture diagrams, database schemas, screen mock-ups, input/output designs, and program specifications. Design may be logical (what) then physical (how on this technology).

Implementation Phase

This is where code is written, unit-tested, integration-tested, and finally accepted. It also covers installation strategies:

• Direct — replace overnight; risky.
• Parallel — run old and new together; safe but costly.
• Phased — roll out module by module.
• Pilot — deploy to one group first, then others.

Maintenance

Over a system's life, 60-80% of total effort goes into maintenance. Four maintenance types:

• Corrective — fixing defects.
• Adaptive — adjusting to new environments.
• Perfective — adding features or improving performance.
• Preventive — refactoring to avoid future problems.

SDLC Models

Several models organize the SDLC phases differently:

• Waterfall — strict sequential order.
• V-model — pairs each dev phase with a test phase.
• Iterative / Incremental — build in blocks.
• Spiral — risk-driven iterations.
• Agile / Scrum — short sprints, continuous feedback.
• DevOps — continuous delivery, blurring dev and operations.

Waterfall vs Agile

Summary

The SDLC gives a common vocabulary for building information systems. Choose the SDLC model that matches how stable the requirements are and how quickly the business needs to see results.

Important Questions

1. Define SDLC and list its phases.
2. What is a feasibility study? Describe its four types.
3. Explain the analysis phase and its deliverables.
4. Compare direct, parallel, phased, and pilot installation.
5. List the four types of software maintenance.
6. Describe the waterfall model. What are its limitations?
7. What is agile software development?
8. Compare waterfall and agile.