Agile vs. Waterfall Software Development: Understanding the Differences

DevOps concept shows methodology options, including Agile and Waterfall.

Just bring up the topic of software development methodologies. You’ll realize that most engineers are biased. Those who favor the waterfall approach are often labeled “old school.” Agile supporters who rigorously adhere to the Agile Manifesto are considered “fanatics.” The truth is, no methodology is perfect for every development project. In fact, many software companies are mixing Agile and Waterfall solutions, trying to leverage the best of both methods.

What is Agile?

Agile is a software development approach that delivers software incrementally. Put simply, it follows the principles of the Manifesto for Agile Software, published in 2001. An Agile approach uses the following phases:

  • Concept. Product owners determine the project scope based on customer requirements. First, they document the features that will be supported and what the end results will be. Second, they estimate the delivery schedule and the costs in sufficient detail. Ultimately, this helps determine a project’s feasibility. 
  • Inception. Product owners assess resource availability to create a team that will design the project. The team looks at customer requirements, such as user interfaces and product functionality.
  • Iteration. The third phase is where the work gets done. It occurs in sprints that typically last two to four weeks. The process goes through five steps. These are plan requirements, code development, software testing, project delivery, feedback, and updates.
  • Release. Developers turn over their code for added testing. Testers determine if the software is functional and bug-free. This phase includes user training and documentation.
  • Maintenance. After releasing the software, development teams provide ongoing support. If bugs are found or inconsistencies appear, they are addressed as part of the Agile process. Upgrades and new features are new iterations.
  • Retirement. When the software is being replaced or is no longer viable, products are retired.

Each step is designed to maintain a customer focus. Fast delivery is a priority. In addition, the process remains flexible enough to incorporate new requirements.

What is Waterfall?

A waterfall model is described as a linear, sequential approach to software development. It progresses through seven steps, from requirement collection to ongoing support and maintenance. Dr. Winston Royce coined the term waterfall when describing the process in industrial design. At its core, each step in the process is completed before moving to the next step, creating a waterfall effect.

The Waterfall software development methodology is composed of the following stages:

  1. Requirements. The required functionality, deadlines, and other project constraints are collected and documented in a functional specification.
  2. Analysis. The specification is used to model the end result. Business analysis determines financial, technical, and operational resources. Ultimately, this step determines the project’s feasibility.
  3. Design. This step is based on the requirements and preliminary model. Design specifications are created that identify hardware, system services, program languages, and architecture.
  4. Coding. Coding begins using the information set down in the functional and design specifications. The overall project may be broken into smaller components that are merged prior to testing. 
  5. Testing. Aside from programmer testing, this phase includes quality assurance, unit, system, and beta testing. Any problems or defects are returned to the coders for correction and retesting.
  6. Deployment. The software passes all testing and is deployed to live or production environments.
  7. Maintenance. Ongoing support is provided to improve, update and enhance the final deliverable. It may include patches or updates. In addition, it might include new versions of the software, depending on the service level agreement (SLA).

Waterfall methods focus on reliable end-to-end performance.

How These Software Development Methodologies Differ

Aside from different terminology, are Agile and Waterfall really that different? After 20 years of Agile and over 50 years of Waterfall applications, many organizations find themselves operating in a multi-method software development ecosystem. 

The end result should determine the methodology. In other words, Agile’s iterative releases work well in a web environment. For example, agile works well for e-commerce merchants who need frequent updates to add functionality to their site. Waterfall’s focus on collecting all requirements before writing a line of code could delay delivery beyond the merchant’s deadline.

Waterfall methods work well in critical application environments such as medicine or space travel. These applications require end-to-end testing. They ensure all components are operational and there are no conflicts. For example, sending a bug fix to imaging software in the middle of a medical procedure will not be an acceptable end-user outcome.

At a high-level, Agile and Waterfall methodologies differ in terms of how fast and how complete a project can be delivered. But how do they differ in the step-by-step processes?

Concept

Step one in an Agile project is similar to Waterfall’s first step. Both steps focus on collecting product requirements. But Agile stipulates the requirements come from the client. Waterfall projects are not prohibited from working directly with the client. However, it is not explicitly stated.

Inception

Agile’s step two brings the project team together to design the project using the requirements collected in step one. In a Waterfall approach, step two puts together a prototype or model. This is then used to determine feasibility. Software projects may include some preliminary lines of code. However, the focus is on delivery and costing.

Waterfall’s step three would fall under inception. This is because it is where the product design is formulated. A design specification is the tool that is used to stipulate how the product is put together. As a result, it identifies programming languages, system architectures, and interdependencies.

Iteration

Within a two- to four-week software development cycle, Agile teams are performing the following on specific features. One use case is building a web form to collect and persist customer data.

  • Defining requirements
  • Writing code
  • Testing software
  • Delivering product
  • Receiving feedback
  • Issuing updates

When this step is finished, the code enters the release process. This is where it undergoes final testing.

With a Waterfall approach, coding falls under this step. The overall project can be broken into units, subroutines, services, or other logical components. They will eventually come together for the final product. The time to complete the coding phase can range from days to years.

Step five of the Waterfall methodology would reside under Agile’s iteration step. This provides the end-to-end testing that ensures that all components are operating reliably and to spec.

Release

Both Agile and Waterfall methodologies have a release step. This involves turning the project over to production for delivery to a client or customer. Ultimately, Agile projects perform their final tests during the release process. On the other hand, Waterfall projects use the release step for deployment in a live environment.

Maintenance

Maintenance for both methods involves ongoing support of the software. It may include bug fixes and updates. And new features may be added in some cases.

Retirement

Waterfall projects do not have a retirement step. But at some point, the software reaches its end of life. The software no longer receives updates or support. As a result, the customer is encouraged to move to the latest version of the product.

How to Choose?

Although the processes follow the same steps, it’s when they use them that has the most significant impact. As mentioned earlier, Waterfall provides an end-to-end, tested solution. On the other hand, Agile delivers incremental improvements and enhancements. In general, Waterfall approaches are more expensive if the software design does not match the final product or significant problems surface during testing. These mismatches are not realized until the end of the project. Unfortunately, this is when making changes is typically more costly and takes longer to correct.

Agile methods can generate stress if looking at a fixed-cost solution. The method is not designed to deliver a comprehensive project assessment. As a result, a project’s cost and delivery may result in higher costs than originally projected. This situation results in an equally poor customer experience. 

To get the most from both software development methodologies, contact EC Group. Our expert developers have extensive experience with both approaches.

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