SDLC vs STLC: What is the Difference?

Software development is a very simple process that starts with system planning and ends with deployment. However, this process becomes more complex when the developers are tasked with creating enterprise-level software solutions instead of small products. The reason behind this is that building complex systems requires a comprehensive software development methodology and quality assurance services. That is why we have concepts like Software Development Life Cycle and Software Testing Life Cycle. 

Both these approaches are useful for creating and managing a high-quality software product. They do have their differences and similarities. Let us understand these concepts in detail. 

1. What is SDLC (Software Development Life Cycle)?

SDLC (Software Development Life Cycle) is a process that every software development company follows to design, build, and maintain working software. SDLC process consists of various phases including planning, requirement analysis & gathering, software designing, implementation of designs & new approaches, testing, deployment, and maintenance.

Each of these phases has dedicated processes and deliverables. If you adopt the software development life cycle then you have to start from conception or ideation for the software by considering the requirements. SDLC is a strategic approach to ensure you build software in a systematic and well-defined manner. This helps software developers meet the customer’s expectations and deliver high-quality results.

Here is what Twitter user says about the software development life cycle.

A Software Development Life Cycle (SDLC) is a structured process for:

Planning, designing, developing, testing, and deploying software.
Managing and maintaining software applications from conception to retirement.
Ensuring quality, reliability, and efficiency in software…

— Fatima zarah 🌸🌷 (@fatoomtyzarah) November 1, 2024

1.1 SDLC Phases

The essential stages of the Software Development Life Cycle (SDLC) are outlined below:

• Requirements Gathering and Analysis

Development teams and project stakeholders gather to analyze the needs for the software project during this phase. Understanding the needs and demands of the end users—that is, customers—is the major goal here.

• Design

In this phase, the app architects consider the project requirements and draw out a suitable software design. It covers every little detail, every single functionality along with the architecture lying underneath.  The designers also describe how your software will look on the client side and how its functionalities will work on the server side. 

• Development

This stage involves writing programs that bring your software designs to reality. The developers write code to build different components and features of the software. The development process is often carried out in numerous sprints or iterations. 

Here each sprint includes the creation of a single feature or component. In the end, all the components and features are integrated to form a fully functioning software. 

• Testing

After completion of the development stage, the product needs to be validated as a single working system along with all its individual functionalities. Test the program thoroughly to identify and fix flaws in new features, ensuring that quality standards are met. Conduct retesting until the program meets the client’s requirements.

• Deployment

The software product is launched and made available to customers or end users once it has passed all testing phases and meets all quality criteria.

• Maintenance

The system is handed over to the team responsible for maintaining it for the duration of its existence at the workplace during the maintenance phase. For service desk workers to be able to send user support requests to the right team, the right paperwork and help files will need to be made.

1.2 Benefits of SDLC

Some notable advantages of using SDLC to create software include:

• Structured Approach

For developers, SDLC provides effective planning, organization of work, and a disciplined approach to software development. This systematic strategy not only reduces mistakes but also improves productivity, ensuring the timely delivery of high-quality software.

• Increases Visibility

Every phase of the SDLC has specific benchmarks and requires particular deliverables. Every activity is recorded, and each step is monitored. Stakeholders may therefore see development at each moment and see how resources are distributed in the name of the objectives.

• Manages Risks Effectively

SDLC is designed to reduce these kinds of risks in the software development process. Its methodical and structural approach begins with appropriate planning and implements many tests throughout every stage of software development. Such testing strategies first highlight possible project risks and greatly lower the project failure risk.

• Cost-Effective

Through the early identification of potential challenges using prototype tools like Figma and others, SDLC helps save development costs. Moreover, early identification of problems gives developers an opportunity act to resolve them, therefore lowering the general development expenses.

1.3 Key Features of SDLC

Some of the key features of SDLC are –

• It comes with detailed documentation of the functions, model structure, and test environment.
• SDLC offers an efficient risk management concept that can be utilized by software developers to reduce their risk exposure.
• It provides a step-by-step approach to software development and testing, which helps in completing the project before the deadline.
• With SDLC, the developers, designers, project managers, and business analysts get a clear understanding of their roles and responsibilities in the project.
• It is a cost-effective process.

1.4 Why SDLC?

Here are the reasons that show why one must choose SDLC in software development-

• SDLC aims to deliver high-quality software applications as per the client’s expectations.
• This process ensures that all the stakeholders are aware of the project and its planning.
• Each phase of SDLC is followed by a formal review, which helps in effective management control.
• It helps you to create considerable system documentation.
• In every stage, including the testing phase, there are entry criteria, exit criteria, and specific deliverables.
• It offers management plan overhead and lowers project risk.
• Enables an efficient and faster software development process.

1.5 Software Development Life Cycle Models

Even if the customer has a vague idea of what they want, there are a variety of software development life cycle (SDLC) models that may assist bring the project to perfection. 

SDLC Models	Key Features	When to Use
Agile Model	In the Agile model, the project is divided into smaller tasks to deliver specific features for a release. An iterative approach is used, and after each iteration, working software functions are delivered. The XP and Scrum methodologies are part of the Agile SDLC framework, and they each use a two-week development sprint approach to covering the SDLC cycles.	The project and team size is big. The project is Complex. Ideal for development over multiple short cycles or sprints. When Continuous integration and Continuous delivery are required.
Waterfall Model	This model was the first SDLC model to ensure the success of the project. The sequential phases in this model are: Requirement Gathering and Analysis System Design Implementation Integration & Testing Deployment Maintenance For the Waterfall methodology to work, each phase must be validated before moving on to the next. This method has the potential to reduce risks throughout the software development process.	The project is short. Ample resources are available to support the project. The project definition is stable. Technology is widely used and not dynamic. Each stage and its requirements are clearly defined.
V-Shaped Model	This model is also known as the “Verification and Validation Model” In this model, the testing phase is parallel planned along with the development phase. The coding phase joins these two phases. Similar to other models, this one breaks the development process down into manageable parts.	The project definition is fixed. Requirements are well defined, and documented. Technology is fixed. The project is short.
Iterative Model	Multiple, smaller software development cycles are used in the Iterative approach. This methodology uses testing to guarantee a successful launch of a software product. This model is often regarded as one of the most effective methods because of the ease with which its development cycle can be broken down into more manageable parts.	Project requirements are clearly defined. Resources with required skill sets are available on a contract basis. The project requires complex functionalities that can change in the future.
Spiral Model	When it comes to software development, the Spiral model is the gold standard. This model has four stages. Identification Design Development Evaluation All the crucial stages of creation are neatly compiled here. This SDLC paradigm simplifies the software engineering lifecycle by doing away with its inherent complications.	Suitable for medium to high-risk projects The budget is constrained and risk evaluation is important. Long term projects Requirements are complex.
Big Bang Model	The Big Bang theory provides no specific rules to follow. When a customer has no idea how the final application will appear, this software development life cycle model was created to assist and guide them through the process.	The project is smaller. The development team is small (2-3 developers working together). The project scope is defined and limited. Ideal for academic or practice projects.

2. What is STLC (Software Testing Life Cycle)?

STLC (Software Testing Life Cycle) is a process consisting of various activities to ensure that the software’s quality is up to the mark. This is a part of the software testing process. The software testing life cycle process is performed by the testing team which ensures the quality of the applications.

STLC ensures that each new release rolls out smoothly and successfully. It is known as an important and integral part of the SDLC. But it only applies at the time of test phases. The stages of STLC may be repeated multiple times while the project is being developed before it goes into the software deployment phase. Besides this, an analysis is conducted of all the different tests in the STLC process and it is documented. This is known as a test closure.

2.1 STLC Phases

STLC Phases	Procedure
Requirement Analysis	The purpose of this stage is to review the feature requirements gathered during the SDLC process and determine which ones can be tested. When unsure of what is expected, testing teams should reach out to stakeholders for input.
Test Planning	A test plan document is created in detail about the testing approach. The plan lays out what will be needed, how it will be tested, and who will be responsible for what. A risk and cost analysis, as well as an expected testing timetable, will play a key role in finalizing this plan.
Test Development	In this step, test cases are developed. Inputs, actions, environments, and outcomes are all specified for each test case. The best test cases are those that are open, effective, and malleable. When all test cases have been developed, you can expect to see full coverage in the tests. During this stage, any essential automation scripts are written as well.
Test Environment Setup	Here, you set up and launch the testing environment. During this time, many testing instruments may be employed, and test servers may be put up. After an environment has been put into production, we can run smoke tests to make sure everything is functioning as it should be.
Test Execution	In this stage, test cases are used to validate features in the deployed environment. The test findings correspond to the expected ones, and any discrepancies are reported to the development teams.
Test Closure	A test results report is compiled at this stage of the STLC. All of the tests should be summarized here, along with comparisons of actual to predicted outcomes. This comparison includes efficiency of the outcomes, total time taken, costs, test coverage, etc.

2.2 Key Features of STLC

Some of the key features of STLC are –

• It determines the system testing type and method.
• STLC analyzes the system requirements that the software development team gathered from clients and stakeholders.
• The STLC process helps in developing a traceability matrix.
• Helps in prioritizing the software feature that needs to be tested the most.
• Describe the test environment setup.
• Assesses automation feasibility.

2.3 Benefits of STLC

There are many reasons to adopt the Software Testing Life Cycle for your project. Here are a few: 

• Early Detection of Defects

During the early phases of software development, the STLC initiative was implemented. This means that errors can be discovered and resolved before they evolve into more severe issues later on. This method addresses problems when they are less costly to fix, therefore saving both time and money.

• Enhancing User Experience

High-quality software delivers a good user experience. By identifying and resolving usability issues, software testing ensures that users can quickly and successfully engage with the system.

• Reduced Development Costs

Early in development, catching errors is considerably less expensive than making repairs later on. By addressing significant issues that delay releases, STLC speeds up time-to-market and reduces post-deployment rework.

• Enhanced Software Quality

Early in the development process, STLC actively analyzes and fixes issues to ensure that the tested software system performs as expected and follows the given standards.

2.4 Why STLC?

Here are the reasons that show why one must choose STLC in software development:

• STLC helps various testing teams to carry out quality improvement activities in different ways.
• It is easy to understand and implement, regardless of the development phase or testing processes.
• In STLC, the execution phase develops a high-quality software release.
• Here tests are conducted on each module of the software before the closure of successful software development.
• It helps in improving the efficiency, and consistency of the software testing process.
• Software testing life cycle helps in improving the quality of the software development.
• It helps in removing the flaws of the software at the early stage.
• STLC assures that clients and end-users of the product receive the best results.
• It helps in optimizing the quality control in the entire SDLC process.

3. Difference Between SDLC and STLC

Let’s have a look at the difference between SDLC and STLC –

Parameters	SDLC	STLC
Definition	Software Development Life Cycle is a process that mainly focuses on developing software that can meet the client’s expectations and work efficiently in the technological infrastructure. Besides, it is a cost-effective process.	Software Testing Life Cycle specifies what type of test activities must be carried out and when should the testing team accomplish those test activities.
Relationship	SDLC is taken as the predecessor.	STLC is taken as the successor.
Focus	The focus of SDLC is on complete software development including the testing process.	The focus of STLC is only on the testing process.
Phases	The SDLC phases are Requirement Gathering, System Analysis, Software Designing, Coding, Software Test Execution, and Deployment & maintenance.	The STLC phases are Requirement Analysis, Test Planning, Designing of Test, Environment Setup, Software Test Execution, and Test Cycle Closure.
Requirement Analysis Phase	In SDLC, the business analyst collects all the requirements and creates a software development plan.	In STLC, the QA team analyses requirements and creates a perfect system test plan.
Design Phase	The SDLC team creates the high and low-level designs as per the project’s requirements.	The test lead or test architect creates the test strategy.
Coding Phase	In the coding phase, the software developers create actual code.	The STLC testing team prepares for the test environment setup and executes test cases.
Testing Phase	Here the actual testing process starts which includes testing types like Unit testing, Integration testing, Regression testing, performance testing, etc.	Actual testing in this phase starts with defect reporting & retesting is done here.
Deployment or Maintenance Phase	In this last SDLC stage, the development team offers support and release updates.	The QA team executes regression suites to check the deployment of maintenance code.
Environment setup	After the code has been produced, the team sets up a test environment to ensure it works as intended.	Developers review prerequisites and perform Smoke tests to verify the test environment is ready and stable.
Maintenance	Support, improvement, and update services after deployment are covered if required.	When checking the newly released maintenance code, the QA team conducts regression testing. The team keeps test cases and automated scripts updated to guarantee accuracy.
Team size	We required more programmers to help with the software development life cycle (SDLC).	The number of testers required to complete the STLC process is smaller compared to SDLC.
Outcome	The outcome of SDLC is that users can get a high-quality software system.	The outcome of STLC is that the users can get bug-free software.

4. Conclusion

As seen in this blog, both SDLC and STLC are the most important aspects of a software development project for creating a perfectly reliable and secure system. SDLC is a methodology that offers a structured and phased approach to product development while STLC validates the projects for their reliability, performance, and functionality.

Though there are many differences, SDLC and STLC have some similarities as well such as gathering requirements, working in iterations, and a common objective of providing high-quality deliverables. More importantly, it’s a well-known fact that testing the life cycle is an integral aspect of the development life cycle.