Software Development Life Cycle Models. What to choose?

It is handy to know which development life cycle model will be useful for you and your team at this current moment. To choose the correct one we need to know how to assess their pros and cons to ensure they meet our needs.

Each model has its strengths and weaknesses, making it suitable for different project types, based on various factors.

Let's explore key software development life cycle (SDLC) models:

• Waterfall (Predictive),
• Iterative,
• Incremental,
• Agile (which combines Iterative and Incremental models),
• Hybrid model.

Waterfall (Predictive) Model

The Waterfall model is one of the oldest and most straightforward development methodologies. It follows a linear, sequential approach, where each phase of the project is completed before moving on to the next.

The phases typically include

1. Requirement Analysis,
2. System Design,
3. Implementation,
4. Testing,
5. Deployment,
6. Maintenance,
7. Closure.

Characteristics of Waterfall

• Each phase is completed before the next begins.
• Since it is linear, it's easy to estimate the time and resources required for each phase.
• Changes during the project are difficult to incorporate once the requirements phase is complete.

When to Use Waterfall

Waterfall is best suited for projects where the requirements are well understood upfront and unlikely to change. It is ideal for low-risk projects with low uncertainty of requirements, and when the client has a clear vision of the end product.

It is also useful in highly regulated environments (e.g., aerospace or healthcare) where processes and documentation need to be tightly controlled and predictable.

For example: Building software for a banking system where security and regulatory compliance are critical, and requirements are fixed and unlikely to change.

Iterative Model

The Iterative model is an approach where the software is developed in small, repeatable versions (or 'iterations').

Each iteration involves going through all the phases of the SDLC (e.g., design, development, and testing) but with a smaller scope.

After each iteration, feedback is gathered and used to improve the product in the next cycle. The product is released at the end of the project in one big shot, the same as in the predictive model.

Characteristics of Iterative

• Each iteration is an opportunity to get feedback from stakeholders and users.
• Changes can be incorporated after each iteration.

When to Use Iterative

The Iterative model is suitable for projects where requirements are not fully understood at the beginning, and there is a need to evolve the product based on user feedback. It works well in environments with moderate risk and moderate uncertainty in requirements.

For example: Developing an internal tool where user requirements are unclear at the outset and need to evolve with stakeholder input after each version.

Incremental Model

The Incremental model involves dividing the project into smaller, manageable components or increments (features).

Each increment represents a portion of the functionality and is delivered separately.

Unlike Iterative development, which revisits the entire project in each cycle, Incremental development adds new functionality to the existing product with each iteration.

Characteristics of Incremental

• Features are added one at a time, making it easier to manage complexity.
• Similar to Iterative, changes and improvements can be made with each increment.
• New functionality is delivered sooner and more frequently.

When to Use Incremental

The Incremental model is handy when the project can be broken down into smaller parts that can be delivered over time. It is useful when there are uncertain requirements but the client needs to see parts of the system early on. It is also effective in medium-risk projects where the priority is to get a working version of the product quickly and improve it over time.

For example: Developing an e-commerce platform where different features (e.g., payment gateway, product catalog, etc.) are released in increments.

Agile Model (Combination of Iterative and Incremental)

The Agile model is a combination of Iterative and Incremental models, designed to be flexible, adaptive, and efficient in dynamic environments. It emphasizes collaboration, frequent delivery of working software, and responding to change over following a rigid plan.

Agile uses short cycles, known as sprints, usually lasting from 1 to 4 weeks (usually 2 weeks), to deliver functionality incrementally.

Characteristics of Agile

• Continuous feedback and close interaction with the client are integral to the process.
• Agile adapts quickly to changes in requirements.
• New features are released frequently and continuously throughout the project.

When to Use Agile

Agile is best suited for projects with high uncertainty in requirements, where the final product is likely to evolve over time. It is ideal for high-risk projects where frequent feedback and flexibility are needed.

The model is also highly beneficial in dynamic industries, such as software startups, where speed and adaptation are essential for success.

For example: Building a mobile app where new features, such as social sharing or chat, are released in phases based on user feedback and market trends.

Hybrid Model (Predictive + Agile)

The Hybrid model combines both Predictive and Agile approaches, making it ideal for projects that require a balance of both structure and flexibility.

It allows for parts of the project to follow the Waterfall methodology (predictive), especially for phases with well-understood requirements or compliance needs, while other parts of the project, typically those with high uncertainty or complexity, follow an Agile approach.

Characteristics of Hybrid

• Critical phases (e.g., requirements gathering or design) can be handled in a Waterfall manner.
• Agile practices are employed for development and testing, where requirements can evolve and are expected to change.

When to Use Hybrid

The Hybrid model is useful for projects where certain parts of the project need to be tightly controlled (such as the planning or initial design phases), but others are more fluid and need iterative development (such as feature development or testing). It's ideal when project complexity or risk requires a balance between structure and adaptability.

For example: Developing a large-scale enterprise software system where the initial planning and design phases are well-defined, but the implementation and user feedback require iterative adjustments and continuous delivery.

To sum up

When deciding which SDLC model to use, consider factors such as the level of risk, the stability of requirements, and the desired speed of delivery.

Waterfall is suitable for low-risk, well-defined projects, while Iterative and Incremental models are more flexible and adaptive, making them appropriate for projects with evolving requirements.

Agile provides a high level of flexibility and adaptability, particularly for projects with uncertain requirements.

The Hybrid model offers a balance between structure and flexibility, making it suitable for projects that require both predictable outcomes and adaptability.

Best, Olha