SDLC vs STLC: What is the Difference?

Software development is a very simple process that starts from system planning to its deployment. This simple process turns out to be a bit complicated when the developers have to create enterprise-level software solutions and not small products. And the reason behind it is that software development for complex systems requires a proper methodology and QA services. This is why the concepts like Software Development Life Cycle and Software Testing Life Cycle have come into the picture. But if we compare SDLC vs STLC, these two approaches are interrelated to each other in some way. 

Both SDLC and STLC are used by software development companies when it comes to creating a product for a specific purpose. But they both differ in some or the other way. In this blog, we will understand both of these concepts and have a look at the difference between SDLC and STLC.

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

SDLC (Software Development Life Cycle) is a process of activities that every software development company follows in order to create working software. This software development process follows proper steps which include planning, requirement analysis & gathering, software designing, implementation of designs & new approaches, testing, deployment, and maintenance.

This means that if any software development team wants to cover the entire life cycle, it will have to start from the conception of the software and its requirements. Besides, the SDLC life cycle consists of different phases which come with their own processes and deliverables. SDLC makes sure that the apps are developed in a systematic and well-defined manner. This helps the software developers to get a perfect end result and meet the customer’s expectations.

1.1 SDLC Phases

• Requirements Gathering
• Analysis Phase
• Design the software
• Development
• Testing
• Deployment & Maintenance

1.2 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 exposure to risk.
• It provides step-by-step 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.

1.3 Why SDLC?

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

• The aim of SDLC is 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 optimum management control.
• It helps you to create considerable system documentation.
• In every stage, including the testing phase, there are entry criteria and exit criteria, development stages, and specific deliverables.
• It offers management plan overhead and lowers project risk.
• Enables an efficient and faster software development process.

1.4 Software Development Life Cycle Models

Even if the customer has a fuzzy 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. Iterative approach is taken 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.	Project and team size is big. Project is Complex. Ideal for the development over multiple short cycles or sprints. When Continuous integration and Continuous delivery is 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, it is essential that each phase be validated before moving on to the next. This method has the potential to reduce risks throughout the software development process.	Project is short. Ample resources are available to support the project. 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 “Verification and Validation Model” In this model, the testing phase is parallel planned along with the development phase. And the coding phase joins these two phases. Similar to other models, this one breaks the development process down into manageable parts.	Project definition is fixed. Requirements are well defined, and clearly documented. Technology is fixed. 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 for contract basis. 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 Budget is constrained and risk evaluation is important. Long term projects Requirements are complex.
Big Bang Model	The Big Bang theory provides no 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.	Project is smaller. Development team is small (2-3 developers working together). 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 that consists of various activities that 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.

Basically, 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 getting 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.
• STLC process helps in developing a traceability matrix.
• Helps in prioritizing the software feature that needs to be tested the most.
• Describes the test environment setup.
• Assesses automation feasibility.

2.3 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 its development phase and 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 vs 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 both complete software development and 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.
Performed	The SDLC steps are finished before the STLC process begins.	The STLC steps are executed once the SDLC phases are complete.
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 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 two most important tools for software development while creating a perfectly secured system. SDLC is a system that offers a structured and phased approach while STLC validates the projects for their reliability, performance, and functionality. Besides, both of these tools are known as the top platforms that serve as a framework for software creation and testing.