What is the software development life cycle (SDLC)

The software development life cycle (SDLC) refers to the step-by-step process developers take to build quality software from its inception to the end product.

An SDLC ensures that the finished product at the end of software development is of exemplary quality, cost-effective, timely, and meets user requirements. While at it, the SDLC goes a long way to preventing project failure.

In this regard, software development is less than a destination and more of a journey, and the steps of this journey make up the software development life cycle.

Every software in use today was once an idea that was refined and thoroughly crafted into a useful end product. And though we may cherish the software, most people don't appreciate its intricate development process.

SDLC is the planned process most companies use to develop high-quality software at optimum costs and timeframes.

In today's highly competitive and demanding environment, most companies don't just want software. They want an application that:

• Is of excellent quality

• Meets cost estimates

• Meets and even exceeds user requirements

• Is developed within given timelines (time is money)

• Has minimal maintenance and running costs

Though these goals may seem far-fetched, they are attainable with a phased approach that enables proper planning and foresight. And this is where SDLC comes in.

Nearly 7 in 10 projects fail. This reality is what pushes most companies to take a structured, planned, and deliberate approach to software development.

The software development life cycle is essential to avoiding project failure, mitigating risks early, and avoiding pitfalls in software development.

The SDLC works by ensuring:

1. Problem breakdown

The SDLC takes the enormous and overwhelming software development process and breaks it down into modular phases that are easy to understand and tackle.

This breakdown also makes the delegation of tasks easier, which saves time and resources.

2. Specialization

The software development life cycle allows for specialization in the development process. Instead of everyone doing everything, it ensures that different parties handle what they excel in—coders code, designers design, and testers test in progression.

3. Visibility and foresight

The SDLC enables the different parties to visualize the end product through the various steps that go into creating it.

It puts the whole software development team on the same page and working towards the same goals throughout software development.

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The software development life cycle will vary from one organization to another since each organization has changing needs.

However, the six stages of software development that are consistent across several organizations are:

1. Planning and requirements analysis

Planning and requirements analysis is the most crucial phase of software development as it sets the stage for other phases. 

During planning, the stakeholders come up with the problem they want the software to solve or the gap they see in the market.

This knowledge allows the developers to ascertain early on:

• The feasibility of the project

• Project objectives

• The total cost of bringing the product to market

• The estimated revenue potential

The developers at this stage go on to perform requirements analysis. In software, requirements refer to a detailed description of the software's capabilities, expected deliverables, and features.

2. Requirements definition

Armed with an idea of the problem, the developers can then analyze the requirements of the software and get a rough idea of what’s expected of the software. This stage makes up the requirements analysis stage.

In this phase, developers define and document the software's functional and non-functional requirements.   

• Functional requirements

These are requirements necessary for the program to function and meet the expectations of its users.

• Non-functional requirements

These are additional requirements that may not be necessary for program function but are still essential for efficient program function.

The defined requirements are then drafted and documented in an SRS (software requirements specification) document that is availed to all parties concerned.

3. Designing of the project architecture

This aspect of the software development life cycle deals with creating a visual representation of the fundamental structure of the software.  

This stage includes defining the system architecture, prototypes, templates, interfaces, and user experience design modules and settling on the programming languages and platforms to be used.

4. Coding and development

This is part of the SDLC, where coders and developers bring the project or parts of the project to life. Teams of developers build KLOCs (thousands of lines of code) for each module or functional requirement of the software.

The modules of each functionality or feature are then integrated into a single and functioning code that becomes the application's source code.

5. Testing and quality assurance

The testing and quality assurance team then takes over this stage of the software development life cycle. This stage aims to test the source code for any potential bugs and fix them immediately.

Quality assurance teams achieve this by subjecting the software to several types of tests, the most fundamental being:

• Unit tests

This includes testing the parts of the program closest to the code. It tests the functions, methods, and classes that make up the source code and assesses if the program works on a modular level.

• Integration testing

Integration testing assesses if the different modules of the program function together.

• Functional tests

Function testing checks if the software meets the deliverables set by the user requirements. Basically, it looks at whether the program functions as expected.

6. Deployment and maintenance

After the above stages of the SDLC, the whole software, part of it, or the minimum viable product (MVP) is launched into the market.

Deployment in most types of software will be gradual. It may start with a minimum viable product and then proceed to the beta version of the software before the final launch of the software as a whole.

The deployment of software isn't an end in itself but a beginning. Going forward, the software must be maintained and updated occasionally to meet changing requirements. 

Though the SDLC may make software development seem relatively straightforward, this isn't always the case.

Often user requirements change while the software is still in development. In other scenarios, the project may come as an emergency with limited timelines.

For these reasons, more specific software development life cycle models are applied to deal with the nuances of application development.

These SDLC models are:

1. Waterfall

Waterfall is one of the SDLC models that has stood the test of time. This model takes a phased and systematic approach to software development, with simplicity as its greatest strength.

In waterfall, the developers move to the next phase of the cycle only after completing the previous phase. The data collected in one phase of the software development life cycle is used in the next. This way, it's like a series of waterfalls, each pouring water onto the next.

2. Agile 

The agile methodology is one of the latter SDLC models. In this model, the large SDLC cycle is broken down into small cycles with minimal turnaround times and clear deliverables.

In agile, developers prefer to discover any issues or bugs early and fix them there instead of waiting for the quality assurance (QA) teams at the tail end of the cycle.

3. Spiral

The spiral model is one of the most widely used models in software development. In this methodology, the developers run the software through the SDLC cycle perpetually until it meets requirements.

It's easier to visualize this model as a spiral because after the last stage of the SDLC, which is testing, the final product is then taken back to the planning and requirements analysis stage.

4. Iterative

The iterative model focuses more on the coding and developing phase of the SDLC. In the iterative model, the developers start coding modules of the software early on in the cycle.

The modules are tested continuously against the requirements and then coded again until they meet all the requirements. That's when these models are deployed.

5. Prototype 

As the name suggests, this SDLC model focuses more on developing a prototype or a minimum viable product in the early stages of software development.

After the requirements analysis and documentation stage, the developers build a prototype.

The finished model is then brought before the stakeholders, who can decide on any improvements and changes in the requirements.

6. V-shaped

The V-shaped model, also known as the verification and validation, is closely related to the waterfall model. The only difference is that the V model adds a corresponding testing phase to each phase of the software development life cycle. 

For example, the requirements phase can run parallel with the acceptance testing, as the system analysis runs parallel with system testing.

The coding and development phases can also run parallel with unit and integration testing and so on.