Software Development Life Cycle: A Guide to Phases and Models

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Published: 19 Aug 2019

Software Development

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People want to build complex things that make our lives easier. Think self-driving cars, smart homes, or augmented reality capabilities built into eyewear.  To make these things a reality, companies need to design powerful software. 

Software is the epitome of complexity. However, no matter how complex, it needs to be flexible, easy to maintain and enhance. How to achieve that? Planning each step of the software development process is a prerequisite for a successful product. 

Understanding the concept of software development life cycle (SDLC) is a great kick-off point towards planning any IT project. This article aims to touch the notion of SDLC, its phases and methodologies. 

First off, what is SDLC? 

Software development life cycle (SDLC) is a series of steps that must be followed by a development team to develop and maintain software. SDLC life cycle starts with a decision to build software and ends with removing it from exploitation. It consists of a set of tasks required to complete at each stage of the development process. 

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Why do IT projects need SDLC? It’s probably the only way to ensure the resulting software meets the demands of a business and users. Poorly planned software projects tend to go out of hand. Budget and deadline breaches. The uncertainty about the project’s future grows, rushed decisions and futile attempts are made in hopes to bring the project under control. With SDLC, clients can enjoy a predictable development process. For software engineers, it means seeing the big picture and understanding what they do and why. 

Why the software life cycle is important:

  • it provides visibility for the engaged parties
  • it allows to control the project
  • predictable deliveries throughout an entire development process
  • eliminating risks like going over budget or deadline breach
  • the process goes on until all the requirements are met

What are SDLC phases? 


Requirements collection 

Goal: to gather and document business requirements 

Discussing the requirements with stakeholders and industry experts is the first step of SDLC. Alternatively, business analysts can use the insights they received from customers. After this stage, everyone should have a clear picture of the scope of the project, budget, resources, and deadline, as well as possible risks and quality assurance requirements. 

All requirements are encapsulated in a formal document – Software Requirement Specification (SRS). This document will be frequently used by project managers, business analysts, and senior software engineers.


Goal: to translate requirements into software design

This stage involves the design of the entire system and its elements. There are two kinds of design, high-level design and low-level design. According to their definitions, a high-level design (HLD) is the overall plan of the system, while a low-level design (LLD) is a design of its components. 

How are they connected? 

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LLD is a detailed description of all the components, configurations, and processes of the IT infrastructure previously described in the HLD. There is no clear set of rules to structuring the System Design Document. It’s written for each project individually, but usually it involves: 


  • Description of the elements of the system and how they interact. For convenience, the information is presented in the form of practical cases (by performing step X, you get the result Y).
  • Implementation. This section provides a summary table that contains general information about the main stages of work necessary for the implementation of the project. 

In addition, HLD contains information about the resources and technologies, as well as information on possible risks, how to prevent them, and ways to recover the system in case of a failure.


  • a description of the layout and connection of equipment
  • a description of software module installation schemes
  • specifications of the operating modes of individual components of the system

Designing software, engineers use proven patterns to solve technical problems with algorithms. A software architect is familiar with most of the patterns and can recommend the most suitable one.

Software development

Goal: To build the actual software 

This is a lengthy phase but less complicated than the previous one. Using the design document, programmers code the modules. The coding tasks are divided between the team members according to their area of specialization. Front-end developers are responsible for creating an interface and it’s communication with the server. Database administrators add the necessary data to the database. In their work, developers use coding guidelines and various tools to write and implement code. The end result of this phase are a working software product and a Source Code Document.


Goal: To ensure the software meets the requirements

After development teams complete programming the software, it’s time for the Quality Assurance (QA) team to step in. The QA team test the software to measure its quality. In this phase, the software undergoes different kinds of testing:

  • Functional testing: Whether software is in line with the requirements described in the SRS. 
  • Performance testing: Testing aimed to find out how the software works under a workload (its speed, responsiveness, and stability).
  • Unit testing: Testing each module individually. If any of them has a flaw, the developer needs to go back and fix it. 
  • Security testing: As the name suggests, this type of testing aims to verify the security of the system. 
  • Usability testing: This type involves testing of user-facing components to find out if the software is intuitive, easy to use, and understandable.

If any bug comes up, it is forwarded back to the development team. After the bug is fixed, the QA team need to re-test it. Quality Assurance is an ongoing process that continues until the software is completely free of bugs and meets the requirements.


Goal: To deliver the software to users

When the software is completed and has no bugs, it is shipped to the market for beta testing. The support team collects feedback of the first users, and if any bugs come up, the development team fixes them. After that, the final version is rolled out. Software updates are implemented at the maintenance stage to make sure it’s tolerant to security breaches.

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SDLC may also entail ideation (or initial planning) and maintenance as separate phases, thus making the 7 stages of the system development life cycle. 

You may also be interested in Most Popular Web Frameworks in 2019.

SDLC models defined

SDLC models allow to plan a software development process effectively and make it predictable. There are different SDLC models in the industry, each of them offering their own approaches to the development process. No matter which model you choose, phases of SDLC will remain the same. Below, we take a look at the two common methodologies. 

Agile Methodology

What is Agile SDLC model?

With the Agile model, development teams can easily adapt to the market situation, as it allows to make changes within at any stage of development. This approach perfectly suits projects with unstable requirements. 

What does Agile software development life cycle look like? Agile lets you build products that customers really want, using short cycles (“sprints”) which end with a working product, although with limited features. Each cycle includes design, development, testing, and deployment. The client or stakeholders get to see the results of each cycle and provide their feedback. In the next cycle, the team revises the product and presents it again for the next round of feedback. As such, Agile development is a continuous process. 

 Agile is easy to identify by its key characteristics: 

  • small deliverables, adding new changes on the go 
  • testing is performed throughout the entire development cycle
  • communication between customers, software engineers, project managers, and Quality Assurance engineers are key. 

Keep reading Web Development Tools Trends and Resources.

What is SDLC Waterfall model? 

Agile and Waterfall are different approaches to software development, both of them being suitable for different kinds of projects. Waterfall model suits projects with stable and defined requirements. 

Waterfall is a rigid model as compared to the flexible Agile model. Because it doesn’t allow for any changes throughout the SDLC  process, the development team only proceeds to the next phase after the previous one has been finalized. It means that there will be only one resulting software, unlike with Agile where each sprint ends with a working product.

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How does the Waterfall model work? It starts with planning and design. Software development is followed by the testing phase and deployment. Because Waterfall is a rigid model, it doesn’t imply the possibility for feedback or changing the requirements at any point along the way. 

Key characteristics of the Waterfall model:

  • a rigid sequence of development steps
  • transition to the next development phase is possible after completing the previous phase successfully
  • fixed cost
  • the customer is not involved in the development process
  • changes can only be implemented after the development process is finalized

Software development is a huge undertaking and requires serious planning, no matter which model you choose. All software begins with requirements gathering and goes through such steps as architecture design, development, testing, and deployment. After that, the SDLC continues with continuous post-launch maintenance, including updates and support, until the software is removed from service. Waterfall and Agile are the most common methods applied in software development, although many companies these days incline towards Agile.

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