The four main software development lifecycle models and how they work

The software development life cycle (SDLC) in software engineering is a methodology that defines the logical steps in the development of a custom software product. This methodology is used to structure, plan and control the software development process.

Simply put, we can define SDLCs as a series of distinct methodologies that a developer can use to standardize the software development process. A number of SDLC models are available, but choosing the right one is not an easy task: and for businesses relying on software, it is essential to ensure that the right model is chosen and implemented.

In this article, we will try to highlight the main pros and cons of some commonly used SDLCs.

1. Waterfall model

the waterfall software development model illustrated

The waterfall method is one of the simplest development models because each step must be completed before the next. (Image credit: Paul Smith/Paulsmith99 (Wikimedia Commons))

This is one of the simplest classical life cycle models, also known as the “linear-sequential” life cycle model. In a waterfall model, each phase must be completed before moving on to the next. A review process is planned at the end of each phase to verify that the project is on the right track. The steps are as follows:

Advantages of the waterfall model

  • Simple to understand and use
  • Each phase is independent of the other phases and is treated and completed separately
  • Suitable for small projects and projects where requirements are clearly defined

Disadvantages of the waterfall model

  • No output or working software is produced until the end of the lifecycle
  • High degree of uncertainty and risk
  • Not a good choice for large projects or ongoing projects

2. Iterative model

the iterative software development model illustrated

The iterative software development model is divided into smaller, manageable iterations composed of phases (Image credit: Krupadeluxe (Wikimedia Commons))

The iterative model can be considered as a “multi-cascade” cycle. Cycles are broken down into smaller, manageable iterations. Each iteration goes through a series of phases, so after each cycle you will have working software.

Advantages of the iterative model

  • Produces working software early in the lifecycle
  • More flexible, as changes in scope and requirements can be implemented at low cost
  • Testing and debugging is easier because the iterations are small
  • Low risk factors, as risks can be identified and resolved at every iteration

Disadvantages of the iterative model

  • This model has phases that are very rigid and do not overlap
  • Not all requirements are met before starting development; this could lead to system architecture issues in later iterations

3. Spiral pattern

the illustrated spiral software development model

The spiral software development model, similar to the iterative model, puts more emphasis on risk analysis (Image credit: Wikimedia Commons)

The spiral model is similar to the iterative model, but puts more emphasis on risk analysis. The steps involved in this model can be generalized as follows:

  1. System requirements are defined in as much detail as possible involving different users, in order to identify different aspects of the system
  2. A preliminary system design is created; this is the most crucial step in the spiral model, as it helps to develop profitable strategies for working on a project
  3. Using the preliminary design, a prototype of the new system is developed; it is usually a scaled-down system, which represents an approximate characteristic of the final output

Consecutive prototypes are then developed using a four-step procedure:

  1. The strengths, weaknesses and risks of the previous prototype are assessed
  2. The requirements for the new prototype are defined
  3. Planning and design of the new prototype begins
  4. The development and testing of the new prototype is carried out

Advantages of the spiral model

  • Good for large and critical projects
  • Working software is produced early in the lifecycle
  • Large amount of risk analysis

Disadvantages of the spiral model

  • Involves a higher cost
  • Not suitable for small projects
  • The success of the project depends on the risk analysis phase; therefore, it requires very specific expertise in risk analysis

4. Prototype model

the illustrated prototype software development model

The prototype software development model overcomes the limitations of the waterfall model (Image credit: Chad250 (Wikimedia Commons))

The prototype model is used to overcome the limitations of the waterfall model. In this model, instead of freezing the requirements before coding or designing, a prototype is built to clearly understand the requirements. This prototype is built on the basis of current requirements.

By examining this prototype, the customer gets a better understanding of the characteristics of the final product. The processes involved in the prototyping approach are illustrated in the image above.

Advantages of the prototype model

  • Benefits from user input
  • As a working model of the system is provided, users get a better understanding of the system being developed
  • Errors and risks can be detected at a much earlier stage, as the system is developed using prototypes

Disadvantages of the prototype

  • Increases overall system complexity
  • Involves an exploratory methodology, and therefore involves a higher risk
  • Involves implementing and then fixing the way a system is built, so that mistakes are part of the development process

Software Development Lifecycles: Summary

Through these four common patterns, you can see the variety of software development lifecycle approaches, with different levels of processes applied. As with all development, quality assurance is critical when it comes to software, and aligning development goals with business strategy is part of a smoother process.

Further reading on software development

With software development, we looked at whether Covid-19 has changed it for better or worse, and explored how you can ensure application security in any of the given development cycle models. Plus, we covered how you can embed continuous improvement in software development, regardless of model, and explained why developers are in high demand as the acceleration of digital transformation continues.

Gordon K. Morehouse