Incremental Model in Software Engineering – What It Is and How to Implement It

The incremental model in software engineering is a development approach in which the product is built and tested in small, manageable segments called increments. Each increment adds new functionality to the previous ones, progressively creating the complete system. This method allows for flexibility, continuous testing, and early risk identification, ensuring a higher quality final product. This model is also known as the Successive Version Model. In this article, we will briefly understand the incremental model, what its requirements are, and where to use it.

What is the Incremental Model in Software Engineering?

Initially, a basic version of the system with essential features is created and provided to the customer. Following this, multiple iterations or versions are developed and delivered, each enhancing the system with additional features and improvements until the final, fully functional system is completed.

Imagine developing a mobile shopping app using the incremental model. First, you create a basic version allowing users to view products and add them to a cart, then deliver it to customers for feedback. Next, you add user registration, login, and checkout features, releasing this updated version. Subsequent increments include payment options, order tracking, and product search, each delivered to customers. Further enhancements, like user reviews and wish lists, are added in later iterations. This process continues until the app is fully developed, with customers benefiting from early use and continuous improvements.

In the incremental model, it consists of four phases, which are mentioned below:

1. Requirement: This is the first phase of the incremental model, where all the requirements are gathered by business analysts and project managers, whether it’s a functional requirement or a non-functional requirement. These requirements are the building blocks for the next phases and software.
2. Design and Development: During this stage, the development team initially prioritises the creation of the fundamental functions of the system that are independent of other features. After the basic elements are complete, they are improved in future versions by introducing additional features. The iterative waterfall model is usually used for developing each successive version.
3. Deployment and Testing: In the incremental model, the testing phase assesses the performance of every current function and any new features. During the testing stage, different techniques are employed to evaluate the performance of individual tasks.
4. Implementation: In the final phase of the incremental model, the product is ready to go live after passing all testing phases. Once the software is fully tested and free of errors, the client reviews and approves it for deployment. Upon deployment, the new functionality becomes available to users. Sometimes, deployment is phased based on the company’s strategy. A user acceptance test allows companies to gather feedback from users in a pre-production environment, ensuring better results before full production.

Also read: How to Become a Software Engineer

Types of Incremental Model

There are two types of the Incremental model:

1. Staged Delivery Model
2. Parallel Development Model

1. Staged Delivery Model: Software is delivered in stages, with each stage adding new functionality to the previously delivered version, allowing for early feedback and use.
2. Parallel Development Model: Development teams work concurrently on separate modules, integrating them once each module is completed, suitable for projects with distinct and independent components.

When to Use the Incremental Model?

Funding Schedule, Risk, Program Complexity, or Need for Early Realisation of Benefits:

• Allows for incremental funding based on delivered increments, reducing financial risk.
• Manages program complexity by breaking down development into manageable stages.
• Delivers essential benefits early, satisfying stakeholders sooner.

When Requirements are Known Up-front:

• Ideal for projects with clear, well-defined initial requirements.
• Supports structured development based on known deliverables.

Projects with Lengthy Development Schedules:

• Facilitates phased development, ensuring continuous progress and feedback.

Projects with New Technology:

• Allows gradual adoption and integration of new technologies.
• Reduces risks associated with unfamiliar technologies through iterative testing and refinement.

Error Reduction:

• Core modules are delivered and tested early, minimising overall project risks.

Divide and Conquer Approach:

• Divides complex tasks into smaller, manageable modules for easier development and integration.

Lower Initial Delivery Cost:

• Reduces upfront costs by focusing on essential features first before expanding functionalities.

Incremental Resource Deployment:

• Allows for gradual scaling of resources as project needs evolve.

Emphasis on Planning and Design:

• Requires thorough planning and design at each increment to ensure integration and functionality.

Superior Requirements Handling:

• Supports development based on prioritised and refined requirements.

Quick Release Demands:

• Enables rapid delivery of basic functionalities early in the development process.
• Provides flexibility to adjust features based on immediate feedback.

Prioritised Requirements Implementation:

• Focuses on delivering high-priority features early, ensuring critical needs are met promptly.

Also read: Waterfall Model in Software Engineering

Advantages of the Incremental Model

• Early Delivery of Functionality: Allows for early release of basic features, providing value sooner and enabling quick feedback.
• Flexibility and Adaptability: Changes in requirements can be accommodated more easily during development, reducing the risk of delivering a final product that does not meet user needs.
• Lower Initial Delivery Cost: Costs are spread out across multiple increments, reducing the initial investment compared to traditional models.
• Early Detection of Defects: Each increment undergoes testing, allowing for early detection and correction of defects, which reduces overall project risk.
• Stakeholder Involvement: Facilitates ongoing stakeholder feedback throughout the development process, ensuring alignment with user expectations.
• Progressive Refinement: Each increment builds upon previous ones, allowing for progressive refinement and enhancement of the software.

Disadvantages of the Incremental Model

• Complexity in Management: Managing multiple increments and their dependencies can be challenging.
• Higher Initial Planning Requirements: Detailed planning and design are necessary upfront to ensure each increment fits into the overall architecture.
• Potential for Scope Creep: Each increment may expand in scope beyond the original plan, leading to delays and increased costs.
• Dependency Risks: Dependencies between increments can introduce integration issues or delays.
• Increased Testing Overhead: Testing effort and complexity can increase with each increment, especially in integrated systems.
• Cost Increases: The cumulative cost of developing and testing multiple increments may exceed that of a single, well-planned project, particularly if the scope changes significantly.
• Requires Skilled Developers: Effective implementation relies on skilled developers capable of modular design and iterative development practices.

Conclusion

In conclusion, the incremental model of software development offers significant advantages such as early delivery of basic functionality, flexibility in accommodating changing requirements, and iterative refinement based on stakeholder feedback. However, it also presents challenges like increased management complexity, the potential for scope creep, and higher initial planning and testing overheads.

Successful implementation of the incremental model requires meticulous planning, skilled resources, and effective project management to harness its benefits while mitigating its inherent risks. Ultimately, its suitability depends on project size, complexity, and the need for adaptive development practices to meet evolving user needs and market demands.