Iterative vs. Incremental Development Explained

Iterative and incremental development are two approaches to software development that emphasize flexibility, adaptability and continuous improvement. They both follow the Agile framework and are used by software developers to manage small and large projects. However, there are some key differences.

Iterative software development aims to build a working product as soon as possible, while continuously adding and adapting new features based on user feedback. It concludes with the deployment of completed software at the end of each cycle. Iterative development cycles commonly include Agile methodologies like scrum and Kanban. These methodologies emphasize collaboration, frequent communication and adaptive planning.

Incremental development focuses on building software in distinct stages. Each stage involves completing an increment of the overall software development cycle and adding it to the final product.  

Here’s what you need to know about each one.

What Is Iterative Development?

Iterative development is a process in which the software is developed in successive cycles, each of which builds on the previous cycle. Each cycle involves a full development process that includes planning, design, implementation, testing and deployment. The goal of iterative development is to deliver working software to the customer early and often, so that feedback can be incorporated into the development process. There are some cases where iterative development is more useful:

• The requirements of the project are not well-defined or may change over time.
• The project is complex or has a high risk of failure.

In an iterative model, a new version of the software is produced after each iteration until the optimal product is achieved. Teams are constantly planning to revisit parts of the system to improve them based on user feedback. Each cycle is intended to bring the solution closer to completion and is always a collaborative process.

Planning and being able to break down larger problems and features into small chunks that can be delivered in a manageable timebox, or a predefined fixed period of time during which activities are completed, is crucial to a successful iterative development process. Realistic timeboxes ensure that work is focused, progress is measured and deliverables are produced within the necessary timeframe.

There are two ways that development may be considered: A requirement focus or a solution focus.

1. Requirement Focus  

There are three different types of requirements that can dictate development:

• Functionality 
• Usability
• Non-Functionality

An individual cycle of iterative development or even the work of a timebox may focus on evolving the solution to meet one or more of these requirement types. On a simple feature, a cycle may encompass all three perspectives at the same time. However, where iterative development of a feature involves many cycles involving several different people, the team may decide to focus a cycle on one or perhaps two specific perspectives rather than covering all of them at the same time.

2. Solution Focus 

This identifies that the solution may be considered to have a number of architectural layers. The below figure used here relates to a business system development but the concept can also be applied to a non-IT project, such as a marketing campaign.

Iterative development may follow an approach in which timeboxes deliver horizontal slices of the solution, vertical slices or a combination of the two.

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Iterative Development Steps

Iterative development typically follows a cyclical process, with each iteration consisting of several steps. Below are the common steps involved in iterative development.

1. Requirements Gathering

The first step is to gather the initial set of requirements for the software. This involves understanding the needs and expectations of the stakeholders and users, the development team works closely with stakeholders to gather and analyze requirements.

2. Design 

Once the requirements are understood, the team moves on to designing the software. The high-level design of the software is created based on the initial requirements. This includes defining the architecture, modules and interfaces. Here are the commonly recognized design types in iterative software development:

• High-level design (HLD)
• Detailed design
• User interface (UI) design
• Database design
• Component design

3. Implementation

The design is translated into code during the implementation phase. Developers write the code for the software components and integrate it to create a working system.

4. Testing 

Once the initial implementation is complete, testing is conducted to identify defects or issues. Various testing techniques, such as unit testing, integration testing and system testing, are employed to ensure the software meets the specified requirements.

5. Feedback and Evaluation 

After testing, feedback is collected from users, stakeholders, and the testing team. This feedback is used to evaluate the software’s performance and identify areas for improvement. It thrives on feedback loops, allowing for continuous improvement. This step provides valuable insights on the software’s functionality, usability and alignment with requirements.

6. Iteration Planning 

Based on the results from the feedback and evaluation stage, the development team plans the next iteration. This involves prioritizing features, setting goals and defining the scope for the next iteration. This step involves several key activities that help establish a clear direction and define the scope of work for each iteration. It provides a high-level understanding of the project’s goals and helps align the team’s efforts.

7. Release and Deployment 

Once the software reaches a satisfactory level of functionality, stability, and quality, it can be released to users. This typically involves packaging the software, creating documentation, and deploying it to the production environment. The key points involved in the release and deployment process include:

• Release planning
• Build and packaging
• Testing and quality assurance
• Deployment planning
• Deployment execution
• Post-deployment activities
• Documentation and communication

8. Review and Refinement

After the release, the development team gathers feedback from users and monitors the software’s performance in the real-world environment. This feedback is used to further refine and enhance the software in subsequent iterations.

Examples of Iterative Development

Below are a few other examples of iterative development:

User Interfaces

Consumers experience the products and create new specifications that are rigorous prioritization down to fewer workdays. In this manner, the system emerges to be beneficial and simple to utilize.

2. Software Prototyping

Prototyping is an iterative approach commonly used in user interface design and user experience (UI/UX) design. The development team creates a basic prototype of the software, which is then tested with users to gather feedback. Based on the feedback, the team iteratively refines and improves the prototype until it meets the desired user requirements and expectations.

3. Web Development

Web development projects can also benefit from an iterative approach. The development team can start by creating a minimum viable product (MVP) with essential features and then release it to gather user feedback. Based on the feedback, subsequent iterations can add new features, improve performance, enhance user experience and address any issues or bugs.

4. Software Updates

When software products receive regular updates, each update can be seen as an iteration. The development team releases updates to address bugs, security vulnerabilities, and performance issues, as well as to introduce new features based on user feedback and market demands. These updates are typically released in iterative cycles, ensuring continuous improvement and evolution of the software.

Benefits of Iterative Development

Iterative development offers several benefits, including:  

1. Reduced risk: By delivering software in iterations, risks associated with the development process are identified and managed early on.
2. Faster time to market: Iterative development allows for the delivery of functional software increments in shorter cycles. This enables the team to release a working product or its features sooner, providing value to users and stakeholders more quickly.
3. Flexible and adaptable: By breaking the development process into iterations, iterative development allows for flexibility and adaptability. It accommodates changes and feedback during each iteration, allowing the development team to incorporate them into subsequent iterations. 
4. Improved quality: Each iteration includes testing and feedback, which leads to improved software quality. Defects and issues can be identified early and addressed promptly, resulting in a higher-quality end product. Functional prototypes are developed early in the project life cycle.
5. Progress is easily measured.
6. Focused testing: Testing is more because the modules are relatively small.

Challenges of Iterative Development:

1. Complex planning: Iterative development requires careful planning and coordination of multiple iterations. It can be challenging to estimate the effort and resources required for each iteration, as requirements may evolve and new priorities may emerge.
2. Continuous involvement and availability: Successful iterative development relies on continuous involvement and availability of clients throughout the development process.
3. Integration and compatibility issues: Integrating new features and increments into an existing system can present challenges.
4. System architecture complications: Issues around system architecture may turn out to be a constraining factor because of the lack of a full requirements specification for the entire system
5. No overlaps: Each successive phase is rigid with no overlaps.

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What Is Incremental Development?

Incremental development involves breaking down the development process into smaller, manageable portions known as increments. Each increment adds new functionality to the software and builds on the work done in the previous increment. The final product is built through the gradual addition of these increments. 

Incremental development is commonly used in various situations where flexibility, adaptability and early delivery of value are prioritized. When the requirements for a software project are not fully known or are subject to frequent changes, incremental development allows for flexibility in accommodating evolving needs. However, it’s not as useful in situations where requirements are well-defined and stable, there’s a fixed timeline and budget, and for small and simple projects. 

Incremental Development Steps

Below are the typical steps involved in incremental development.

1. Requirement Analysis 

In this initial phase, the development team works with stakeholders to define and prioritize the requirements for the software. The team identifies the most critical or high-priority requirements that will be included in the initial increment.

2. Design and Planning

The team designs the architecture and framework for the software system, considering the requirements defined in the previous step. The planning phase involves identifying the functionalities to be implemented in the initial increment and defining the timeline and resources required for its development.

3. Development of Initial Increment 

The team starts developing the initial increment of the software. This typically involves implementing the core functionality or features that are essential for the software to provide value. The development is done in a focused and iterative manner, ensuring that each increment is implemented, tested and integrated with the existing system.

4. Testing and Evaluation

Once the initial increment is developed, it undergoes testing to ensure that it meets the specified requirements and functions as expected. The testing phase includes unit testing, integration testing and possibly user acceptance testing to validate the functionality and identify any defects or issues.

5. Review and Feedback

The stakeholders and end-users review the initial increment and provide feedback on its functionality, usability and alignment with their requirements. This feedback is crucial for guiding subsequent increments and making necessary adjustments or improvements.

6. Development of Subsequent Increments 

Based on the feedback received, the development team proceeds to develop subsequent increments, each of which adds new functionality to the software. The increments are developed in priority order, focusing on delivering the most valuable features first.

7. Integration and Deployment

As each increment is developed and tested, it is integrated with the previously developed increments to form a complete software system. The integrated software is then deployed to the end-users or customers, who can start benefiting from the added functionality.

8. Iterative Improvement

The development process continues in an iterative manner, with each increment building upon the previous ones. The team collects feedback, evaluates the software’s performance, and refines the requirements for subsequent increments.

Incremental Development Examples

Here are a few examples of how incremental development can be applied:

1. Content Management System (CMS) 

A team is tasked with developing a CMS that allows users to create, manage, and publish web content.

2. Mobile Application 

A team is developing a mobile application for task management. The initial increment may focus on creating a simple interface for creating and managing tasks.

3. Project Management Software

The development team is building a project management software solution. They begin with the fundamental features like task lists, assigning tasks and basic project tracking.

4. E-commerce Platform

The development team is building an e-commerce platform. They start with the basic functionality, such as product catalog, shopping cart and checkout process.

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Incremental Development Benefits

Incremental development offers several benefits, including:

1. Less risk: By breaking down the development process into increments, incremental development helps mitigate risks.
2. Enhanced quality: With each increment, there is an opportunity to validate and test the software.
3. Flexible and adaptable: Incremental development accommodates changes in requirements and priorities. As new functionality is added in each increment, it allows for the software to evolve and adapt to changing needs, market conditions or user feedback.
4. Early value delivery: Incremental development allows for the early delivery of functional software increments. 

Incremental Development Challenges

1. Incremental planning: Planning and coordinating the development of multiple increments can be challenging.
2. Requirement volatility: Incremental development relies on requirements evolving and being refined throughout the development process.
3. Documentation and knowledge management: As the software evolves through multiple increments, maintaining up-to-date documentation and knowledge transfer can become challenging.
4. Increased complexity: As functionality is added with each increment, the system becomes more complex, which can make it more difficult to manage and maintain.
5. Difficulty in estimation: Incremental development can be challenging to estimate accurately.