SDLC Models in Software Engineering
The Software Development Life Cycle (SDLC) is a structured framework used in project management to guide the development of an information system from the initial feasibility analysis to the ongoing maintenance of the finished application.
Over time, various SDLC models have been designed to outline and organize the software development process. These are often referred to as "Software Development Process Models". Each model follows a distinct sequence of phases, tailored to its methodology, to ensure efficiency, quality, and success at every stage of software creation.
Waterfall Model
The Waterfall Model is one of the most widely recognized and traditional SDLC models. In this approach, the entire software development process is divided into distinct, sequential phases.
Development flows in a linear and downward direction much like a waterfall through the stages of requirements analysis, design, implementation, testing (validation), integration, and maintenance. Each phase must be completed before moving on to the next, ensuring a clear and structured progression.
The linear ordering of activities has important implications. To clearly mark the end of one phase and the start of another, formal review or certification techniques are applied at each stage. Verification and validation processes ensure that:
- The output of each phase aligns with the input from the previous phase.
- The deliverables remain consistent with the overall system requirements.
RAD Model
The Rapid Application Development (RAD) Model is an adaptation of the traditional Waterfall Model, designed to deliver software in a much shorter time frame. It emphasizes speed and flexibility, focusing on quickly gathering requirements and rapidly building functional prototypes.
RAD operates on the idea that involving focus groups and end-users early in the process helps capture accurate requirements, resulting in a better-quality system developed in less time.
The RAD process typically involves the following phases:
- Business Modeling – Defining the flow of information and identifying business functions.
- Data Modeling – Designing the data objects needed to support the business model.
- Process Modeling – Defining processes and workflows to manipulate the data objects.
- Application Generation – Using automated tools to quickly create the actual system.
- Testing and Turnover – Validating the system and handing it over to the users.
Spiral Model
The Spiral Model is a risk-driven SDLC approach that combines elements from multiple process models such as Waterfall and Incremental while integrating rapid prototyping and concurrent design-development activities.
It is particularly effective for large, complex, and high-risk projects, as it allows continuous refinement through repeated cycles, or “spirals.”
Each spiral cycle consists of the following key steps:
- Identify Objectives and Constraints – Define the goals for the cycle, explore possible approaches to achieve them, and note any limitations. (Upper-left quadrant)
- Evaluate Alternatives and Risks – Assess the possible solutions, focusing on the risks that could impact the project.
- Resolve Risks – Develop strategies to address uncertainties, which may include activities like benchmarking, simulations, or building prototypes.
- Development and Planning – Proceed with development for the cycle and plan the next iteration.
V-Model
Incremental Model
The Incremental Model is essentially a sequence of smaller waterfall cycles rather than a standalone approach. At the beginning of the project, requirements are divided into manageable groups. For each group, the standard SDLC process is applied to develop a portion of the software. With every iteration, a new release is produced, adding more features and functionality until all requirements are fulfilled.
In this approach, each cycle also serves as a maintenance phase for the previous release, ensuring improvements and fixes are incorporated. A modified version of the incremental model allows development cycles to overlap, enabling the next cycle to begin before the current one is fully completed.
Agile Model
Agile methodology is a software development approach that emphasizes continuous collaboration between development and testing throughout the SDLC. In this model, the project is divided into small, incremental builds, each delivered in iterations lasting one to three weeks.
The Agile approach is based on key realities of most software projects:
- It is often impossible to determine in advance which requirements will remain unchanged and which will evolve. Likewise, user priorities may shift as the project progresses.
- For many types of software, design and development are interwoven. Both activities should be carried out together so that design concepts can be tested and validated as they are created.
- The amount of design needed before construction begins is difficult to predict; iterative building allows early testing to guide further design decisions.
- Planning for analysis, design, development, and testing is less predictable than in traditional models, making flexibility and adaptability essential.
Iterative Model
The Iterative Model is a software development approach that begins with an initial, simplified version of the application. With each iteration, the system is refined, expanded, and enhanced, gradually increasing its complexity and feature set until the final product is complete. In essence, iterative development breaks down the creation of a large application into smaller, manageable cycles, allowing for continuous improvement and adaptation throughout the process.
Big Bang Model
The Big Bang Model is a software development approach that focuses primarily on coding and development, with minimal or no upfront planning. Requirements are addressed and implemented as they arise, rather than being fully defined at the start.
This model is best suited for small projects with a compact development team working closely together. It is also popular in academic or experimental software projects. The Big Bang Model is ideal when project requirements are unclear or when there is no fixed deadline for the final release.
Prototype Model
The Prototype Model begins with requirements gathering, where the developer and the user collaborate to define the software’s purpose, identify needs, and outline key functionalities.
Next, a quick design is created, focusing on the elements of the software that will be visible to the user. Based on this design, an initial prototype is developed and presented to the customer for review.
Feedback from the customer is then used to refine the prototype. This iterative loop building, reviewing, and modifying continues until the customer is fully satisfied. Each improved version of the prototype is shown to the user, ensuring that all requested changes are incorporated.
Once approved, the final prototype is transformed into the complete system, with full attention given to quality, performance, and security.