# Software Development Life Cycle (SDLC)

The Software Development Life Cycle (SDLC) is a structured process used by the software industry to design, develop, and test high-quality software. It aims to produce high-quality software that meets or exceeds customer expectations, reaches completion within times and cost estimates.

## 1. The Phases of SDLC

The SDLC typically consists of the following stages:

### 1. Planning and Requirement Analysis
The most fundamental stage. Senior members perform requirement analysis with inputs from the customer, sales department, market surveys, and domain experts.
*   **Goal:** Define *what* needs to be built and feasibility (technical, operational, economic).

### 2. Design
Based on requirements, the system architecture is defined. This is often documented in a Design Document Specification (DDS).
*   **High-Level Design (HLD):** Architecture, database design, interface design.
*   **Low-Level Design (LLD):** Detailed logic of modules, error handling.

### 3. Implementation (Coding)
The actual development starts here. Developers write code according to the design documents and coding standards.
*   **Goal:** Translate design into executable code.

### 4. Testing
Code is tested against the requirements to ensure it solves the needs gathered during the planning phase.
*   **Types:** Unit testing, Integration testing, System testing, Acceptance testing.

### 5. Deployment
Once tested, the software is deployed to the production environment. This might happen in stages (Alpha, Beta, Production).

### 6. Maintenance
After deployment, the software needs to be maintained.
*   **Bug Fixing:** Fixing issues reported by users.
*   **Upgrade:** Adding new features or upgrading to newer platforms.

## 2. Common SDLC Models

### Waterfall Model
The classic, linear approach. You finish one phase completely before moving to the next.
*   **Pros:** Simple, easy to manage.
*   **Cons:** Inflexible. Changes are expensive once a phase is passed.

### Agile Model
An iterative and incremental approach. The product is broken into small incremental builds.
*   **Pros:** Flexible, faster delivery of features, high customer involvement.
*   **Cons:** Documentation can get left behind, scope creep.

### DevOps
Combines development (Dev) and operations (Ops) to shorten the systems development life cycle.
*   **Focus:** Automation, CI/CD, monitoring.

[[programming/agile-methodology]]
[[programming/ci-cd-pipelines]]
[[programming/software-testing-basics]]