Incremental Model vs Spiral Model

The software development life cycle (SDLC) is a continuous process, which starts from the moment when a company takes a decision to create software and ends up at the moment of its release. SDLC models define the phases the software goes through to be delivered. Software quality, budget, timeframes, and ability to meet the client’s expectations largely depend on the chosen model.

There are more than 50 software development methodologies and they all have both pros and cons. So none of them is perfect however they all work best in different scenarios. In this article, we will take a look at the essence of incremental and spiral models and compare their core features.

Incremental Model

An incremental model is a software development model where the software is analyzed, designed, developed and tested incrementally (a little more is added each time) until it is finished. The software development process ends when the product meets all requirements.

The software is broken down into a number of components, each designed and created separately. Every component is presented to the client upon completion therefore it is easier to modify the version when necessary. Also, this model helps to ease the introduction of a completely new system and avoid a long development time.

The development team first builds the core features of the software and then refines them in the subsequent iterations. As every subsequent version of the software is delivered, the client provides feedback that is incorporated in the next iteration. Each iteration adds more functionality to the previous release.

Advantages of Incremental Model

• The working software is produced quicker and earlier during the software life cycle.
• The process is more flexible.
• It is less costly to make changes in software through the development stage.
• It is easier to test and debug due to smaller iterations.
• It is easier to manage risk because risky components are identified and handled during its iteration.

Disadvantages of Incremental Model

• Refining in one iteration requires changes in all the other software versions which is time-consuming.
• It needs thorough planning and design.
• Issues in software architecture may arise if some of the requirements aren’t collected before the development stage.
• Each iteration is rigid and does not overlap with each other.
• Requires a clear and complete definition of the whole system before it can be broken down into components.

When to Use Incremental Model

This model is effective when the requirements are well defined and there is a clear understanding of how the system will be decomposed.

This model is popular in web application development and among product-based companies. Besides that, the model can be used when there is a need to deliver a product to the market early. On top of that, the incremental model can be used in the following scenarios:

• New technology is being used.
• Specialists with needed skills can hardly be found.
• There are some high-risk features and goals.

Spiral Model

The spiral model looks like a spiral with many loops. The loops are called phases and the number of the loops needed to create software can vary depending on the project risks. Project managers play an important role in the spiral model since they determine the number of phases the software development process will go through.

The radius of the spiral represents the expenses of the project, and the angular dimension represents the progress made. The phases in the spiral model are similar to the ones in the iterative software development model. The software is built during the first phase and refined in the subsequent phases. Each phase is divided into the following stages:

1. Objectives identification. Requirements are gained from the client and the objectives are identified and analyzed. Then alternative solutions are introduced.
2. Risk management. It involves the evaluation of all potential solutions in order to find the best one. The risks associated with this solution are then identified and resolved.
3. Development and testing. During this phase, the software is built and tested for quality. The components are developed and integrated to form a complete software product or a prototype. In the early cycles, the software at this phase is a prototype and in subsequent cycles, it is a fully developed software product.
4. Evaluation. It determines whether the goal set at the first stage has been achieved or not. The evaluation phase also helps the development team to identify how many cycles will be required to complete the whole project.

The spiral model is where intensive client engagement is needed. The client is usually involved in the objectives identification and evaluation stages of each cycle.

Advantages of Spiral Model

• It is easy to make changes and add features to software.
• It is easy to estimate the cost because software is built in small sets.
• Making changes continuously helps to manage risks.
• The development process is faster because features are added systematically.
• Clients are involved in the development process to provide timely feedback.

Disadvantages of Spiral Model

• It is costly for small projects due to multiple iterations.
• It involves intermediate phases with too much documentation.
• The stages of development need to be followed obediently.
• It requires an expert in risk assessment.

When to Use Spiral Model

The spiral model is a risk-driven model that puts focus on thorough risk assessment. It is suitable for long-term projects where the client is not able to specify all the requirements explicitly or the business requirements may change in between the project. Therefore, it is used in software development projects with unclear business needs or ambitious requirements. Moreover, the model can be used for projects where the requirements are complex and there is a need for frequent evaluation.

Bottom Line

Every business strives to achieve maximum productivity using minimum resources. Both incremental and spiral models may help them achieve this by determining optimal resources for every phase of the software development life cycle. They can guide you in the right direction and help you harmonize your business processes. However, you should keep in mind that they are efficient in certain scenarios. There is no only one suitable model for all projects since each of them has different business requirements and budget.

If you would like to get a clearer understanding of which software development model will fit your project best – or if you need a top-notch software development team to develop your software – drop us a message on our contact page.