Fixed or Flex? Which Software Development Model is Right for You?

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by Sydney Stone

The software development life cycle (SDLC) involves many different stages of production, including concept, design, development and testing.

Most software development models fall into one of two categories: fixed or flexible. Fixed development methods include Waterfall, Rapid Application Development (RAD), and Spiral. Agile and Extreme Programming (XP) are two examples of popular flexible development models.

Deciding which one of these software development methodologies works best for your project doesn’t have to be complicated. In this blog post, we’ll take a look at the benefits of both fixed and flexible methods when it comes to software development.

Fixed methods

Fixed (or structured) is the more traditional method of software development. It’s a project management style based on linear processes and definitive deadlines. Each phase of development must be completed and approved before moving on to the next.

Some of the most popular fixed development methods include:

Rapid Application Development

Rapid Application Development (or “RAD”) is a trial and error development method focused on prototyping and rapid delivery. RAD is comprised of short development cycles that happen over the following phases: business modeling, data modeling, process modeling, application generation, and testing & turnover.

Because all planning and analyzing happens while the product is being developed as opposed to prior, a prototype can be delivered quite quickly and efficiently.


The waterfall process is a sequential approach to software development. It involves planning and scheduling each and every aspect of the development cycle prior to the commencement of the project and then working on each phase in a linear order.

There are five basic phases that make up the waterfall development process. They are requirements, design, implementation, testing, and maintenance.


The spiral model of software development is similar to the waterfall method, but places much more emphasis on risk assessment and is viewed as an expanding spiral of activities as opposed to a top-down approach.

There are four aspects to the spiral method: determining objectives, assessing risks, developing & validating, and planning the next step (or “loop”).

Flexible methods

Flexible methods of software development have more expansive timelines and budgets and tend to involve the client much more than in structured processes.

Some of the most popular flexible methods of development include:


Agile system development is the most popular software creation methodology used today. It is based on collaboration between all stakeholders involved in the project, including the client, programmers, user groups, QA experts, and others.

The Agile software development life cycle involves a series of “sprints” in which components of the solution are created, reviewed, and tested before moving on to the next sprint. Each sprint is made up of a list of certain deliverables for a specific time period. This cycle continues through each phase of development until the product is ready for release.

Scrum software development is a form of Agile that is used by many development teams and agencies.

Extreme Programming

Extreme Programming – also referred to as XP – is basically Agile on steroids. This method promotes short development cycles and “checkpoints” that allow new features or requirements to be added.

In XP development, code is reviewed on a constant basis and emphasis is placed on verbal communication over time-consuming written documentation.  

Which method should I choose?

Deciding which of these software development methodologies to use will depend on the specifics of your particular project.

If you have a limited budget and time frame, structured software engineering models will work best for you because you’ll know exactly how much the project will cost up front and when it will be finished. Keep in mind, however, that with this approach, you won’t be as involved in the development process and may end up with a product you’re not completely happy with.

Structured development also works well for companies with limited IT resources, as the development team is able to work on other projects while the planning phases are taking place.

On the other hand, flexible methods such as Agile will provide you with a more customized and finely-tuned product. Flexible methods allow the solution to grow and improve throughout the entire development phase and result in a better product with a higher chance for user adoption.

Software development life cycle phases will differ based on the team you are working with. Whether you choose to have your own in-house programmers or work with a highly qualified outsourcing agency, it’s always a good idea to discuss your goals with your developers ahead of time. They are the ones best qualified to point you in the right direction.