Agile Vs Waterfall - When to use Agile and Waterfall?

When to use Waterfall Model?

Every software development project is different and requires a suitable software development life-cycle approach that is employed based on your team and organization's internal and external factors. There are some project situations where the Waterfall model is appropriate, but as we look at these, you may feel from experience that this doesn't always work out.

First, Waterfall is suitable if your requirements are well documented, clear, and fixed. How often is that the case though? From my own experience as a software developer, I can't remember any of the many projects I've delivered where the requirements have been clear from the start so that they can be captured in a document that doesn't change as the project rolls on.

Next, the product definition must be stable. Again, I can't think of a single project where this has been the case, as external factors like a change in the marketplace or a shift in business priorities mean that your product will change over time. I have worked on many projects where the final delivered product was quite different from what was initially specified. Under Waterfall this shouldn't happen, but in reality, what you are building can change.

There is nothing wrong with this, but it does fight against the software delivery process. Hold this thought in your mind, as this will form a big part of our core theme when we discuss Agile in detail later on.

Next, the technology should be well understood. This means that developers should understand the technologies that they're going to be using and how they work. Once you enter the implementation and construction phase of the project, developers normally have to work toward very rigid and set-time scales. In my experience, a lot of effort is expelled on the requirements and design phases, which normally eat into the time needed to actually develop the code.

Next, Waterfall works best on projects that are short, and by short I mean projects that take around two-to-four months in total. The longer a project runs, the more chance there is of the requirements and product definition becoming out-of-date.

Finally, Waterfall works best when all the members of your project team are available. It is quite normal for a development team to have a pool of resources that might be shared out between many different projects. If another project is overrun for any reason, you may not have all your people available at the time when they are required. This can greatly impact a project's time scale and put delivery dates at risk.

When to use Agile Model?

Agile Model limits the time needed to be spend in planning the project. It adopts the ever changing needs of end users through providing incremental releases and improve over the time. Whenever there is uncertainty in the requirement and need some degree of innovation to proceed agile model helps achieve success in any project.