Core Difference Between SDLC and STLC

SDLC and STLC are both important frameworks to ensure software products are built efficiently, meet business requirements, and maintain high quality. But the difference between SDLC and STLC is significant. SDLC focuses on the creation and delivery of software. On the other hand, the software testing life cycle ensures the testing and quality assurance of that product. 

Both are simultaneously working for any software development project to maintain a standard quality. They are deeply interconnected with each other. Testing doesn't wait until development ends. 

So, what are the SDLC vs STLC differences and the relationship between SDLC and STLC? Let's find out in this blog. We go through every detail and break down each section easily, so that all the confusion is cleared away.

Let's start.

What Is SDLC (Software Development Life Cycle)

SDLC =  software development life cycle 

SDLC is a structured process that combines the (plan, design, build, test, and deploy). This process is used to build high-quality software development or app development. A total go-through process of idea generation to post-launch maintenance in any project. With SDLC, a company can achieve their desired goal and also reduce the hidden costs of the project. SDLC has different work tasks in each phase and a time limit. You need to complete each phase properly to take the next steps. All of the phases are well documented, so if anything needs to change in future, it can be easily changed.

Key Characteristics Of SDLC

Every model has some characteristics, and the SDLC is not different. Characteristics are the term that can define a person; just as in any project, it defines how this model works. Below, you can get an idea about those :

• SDLC follows a well-defined structural process 
• The main aim is to deliver high-quality software
• Phase-Based Approach
• Phase has its own timeline and deliverables
• Each step is well documented
• Team Collaboration Process 
• Ensure accuracy, reliability, and performance
• Proper risk management 
• Continuous upgrade and improvement 

Different SDLC Models In Software Development 

The software development life cycle method is not only a single model used to build software. There are other models as well. Include :

• Waterfall Model
• Agile Model
• V-Model
• Spiral Model
• Incremental Model
• RAD Model

Each method is well structured and balanced. Choosing any of those models basically depends on your project goal, budget and requirements. 

Why You Need SDLC in Software Development

The importance of SDLC in software development is quite massive. Proper planning and a well-documented model always provide the best output in any circumstance. Suppose you want to build a restaurant software, and your focus is on the billing system and appointment system. For that, you need a proper plan and a proper team, and most of all a well-organised project plan. Without a proper plan and a proper model, you may face different problems. Include hidden costs, defect issues, unclear requirements, lack of documentation, project delays & more. In the long run, the development software does not perform well, and it costs the reputation of the brands. 

DIfferent Phase Of SDLC

Same as the STLC, the SDLC has several phases, and each stage has different tasks to do. So let's check at a glance :

The phases of sdlc include:

• Requirement Gathering and Analysis
• System Design
• Implementation or Coding
• Testing
• Deployment
• Maintenance

What Is Software Testing Life Cycle

STLC = software testing life cycle 

STLC, is a process that goes through several stages of testing and finds any defects in the development software project. It's basically to ensure quality assessments and software testing. It's a detailed process of finding out all the errors or bugs and fixing them through several phases. 

STLC ensures that the software meets the actual standard, customer satisfaction, and maximises ROI. Through its several phases, it has to complete this process. This whole testing process is performed by the testing QA assurance team.

Key Characteristics of STLC

Software testing is an important part of any software development project. Without any doubt, software testing maintains a standard level of software deployments. There are, though, some characteristics of STLC that they follow to process any project. Those are :

• Follows a structured sequence of phases 
• Ensuring software quality and reliability
• Phase-Based Approach
• Each phase has specific outputs, such as test plans, test cases, and defect reports.
• Testing activities start early
• Feedback from each cycle to improve future testing processes
• Identifies and mitigates potential risks during testing
• Involves systematic recording, tracking, and resolving of software defects.
• Track the correctness (verification) and usefulness (validation) of the existing project 
• Collaboration & Communication through the team 

Why You Need STLC in Software Development 

Customer positive feedback is always a positive sign for any ongoing development project. Bug-free software is always maintainable for the buyer. So, STLC provide this service and ensures an excellent user-friendly software experience. Without this phase, customers may face buggy software, and at the end of the day, customers give a bad review of the software. It's cause the brand reputation and loss of royal customers. This is one of the reasons you must practice this process before deploying any software in production. Another important thing to remember is that it also reduces the unusual cost of the project. 

Different Phases of STLC

Basically, STLC combine six different phases. Each phase has different responsibilities from the other phases. If the phase 1 work is not complete, then it's not possible to move to the next phase. 

The six different phases of STLC 

• Requirement Analysis
• Test Planning
• Test Case Development
• Test Environment Setup
• Test Execution
• Test Closure

All The Difference Between SDLC and STLC

Both are works in software-related fields, but their work processes differ. In this section, we will examine the total difference between these two Sdlc and Stlc. Find out the real difference between them.

Difference Between SDLC and STLC in Software Engineering - At a glance 

Phase-Wise Comparison Between SDLC and STLC

Phase 1: Requirement Analysis

SDLC

In the SDLC phase, Business analysts and developers gather all the requirements for the assigned project from stakeholders. The main focus in this phase is on what to build and all the requirements gathering.

STLC

This phase is assigned to the QA team and the tester. Their ultimate goal is to find the requirements to identify testable components and prepare a requirement traceability matrix.

The difference in SDLC vs stlc life cycle is in phase 1

SDLC - Functional scope

STLC - Requirements are verifiable and testable.

Phase 2: Planning

The name of the phase declares what this phase is doing. The planning phase defines the total planning and process of the two SDLC and STLC. 

SDLC

If we're talking about the SDLC phase, then it's all about the project plan, resource allocation, and cost estimation. How this project plan gets started, and the overall cost of the project, all those things are included in these phases.

STLC

On the other hand, the STLC phase is all about planning, detailing the testing scope, objectives, and tools to be used. The QA team and testing team select the tools and the objective for each of them, and prepare for the next steps.

Key SDLC vs STLC difference - Phase 2 

• SDLC plans for the entire project execution
• STLC plans for the testing strategy within that project

Phase 3: Design

Phase 3 is all about the design and process of the work in software development.

SDLC

In this phase, the developer and the development team translate the requirements gathered during the previous stages into a technical blueprint of the system. This all includes the high-level design and low-level design. The main aim is to understand what needs to be built and the final design of the project.

STLC

In phase 3 of design in STLC, the testing will be conducted based on the system's design documents. The QA team and testing team ensure the case design and test data creation, and other staff as well.

Key difference between STLC and SDLC 

• SDLC: how the system will work 
• STLC: How the system will be tested

Phase 4: Development and Coding

SDLC

In the SDLC, actual coding begins with the developer according to the design and requirements. The developer might talk with other team members and communicate with them. They also need some software for their work. They write the code according to the design and others' work.

STLC

In STLC, testers need to perform some tests and unit test preparations or test environment setup. They might have needed tools and other equipment to do some test work.

Key Difference:

• SDLC produces the software product
• STLC prepares to test that product

Phase 5: Testing

Testing is all about the testing process of the software development sections. In this process in SDLC and STLC 

SDLC

In this phase, developer work is mostly done. They have done all their coding and development; it's time to hand over this code to the tester team to test it. So the QA team is assigned to do their checking process and find out if there are any bugs or defects. If the answer is then the QA team gives it back, and the developer fixes it, and then they again check it. This process is continuously done if the bugs are found again.

STLC

In this phase, the STLC aims to produce defect-free, stable, and ready for deployment software developments. Include :

• Executing test cases 
• Comparing actual results with expected outcomes
• Logging and tracking bugs using testing tools
• Retesting after defects are fixed to confirm resolution

Key Difference in stlc and sdlc 

• The developer sends it to the QA team for testing 
• STLC is entirely dedicated to testing and quality assurance in software testing

Phase 6: Deployment

Another difference between SDLC and STLC is the deployment stage. In this stage, basically it's handover to the users' sections to find out any defects or bugs that are still in the project or the experience with this software before the deployments. 

SDLC

In this phase, the Software is deployed to production for user access. After the production is complete, it's time to collect the user experience of the development products. User give their valuable opinions, and if there's still anything missing, it's high time to fix it before it goes live. This is the last stage of the SDLC model.

STLC

Before proceeding to the final stage, Testers conduct post-deployment validation or user acceptance testing (UAT).  Find out any errors that occur and fix them. 

Key difference between SDLC and STLC

• SDLC ends with deployment
• STLC ensures the deployed software functions correctly 

Phase 7: Maintenance

It's time to maintain it properly with customer feedback or regular updates. If your competitors also bring updates, then you need to make changes to survive in the market. If your target is to lead the market, then always bring a quality upgrade to the software after releasing it. 

SDLC

In this phase, developers need to check and maintain it. The main goal of this phase is to handle updates, enhancements, and bug fixes. 

STLC

On the other side, the software testing life cycle phase theme is the same, but the process is different. The testing team is assigned to Regression testing and re-testing before it submits for the next phase. 

Key difference between SDLC and STLC

• Software performance
• Software quality after release

SDLC Vs STLC: Based on Role & Responsibility

SDLC and STLC are not a one-person job. To complete this process, it's handed over to different people. Each of the people has a different responsibility. Below, we made a comparison table that can provide a detailed idea about it.

When to Choose SDLC And STLC in Software Development 

When we talk about choosing one after another, then it's a tough thing to do. But we can give you a total idea about it. Choose the right process at the right time for better project efficiency and product quality. 

When Choose SDLC

• Starting a new software project for the software company 
• You need structured project management
• You are developing large or complex systems
• You need coordination among multiple teams
• There are strict client or business requirements
• You are using Agile, Waterfall, or Hybrid approaches
• predictable outcomes and software cost estimation

If these are the criteria, then go for the software development life cycle. 

When Choose STLC

• The development phase is completed or near completion
• You want to ensure product quality and a defect-free release
• You are testing new features or modules
• The system involves high user interaction (UI/UX heavy)
• Ensure security and performance
• Maintain or update existing software & more 

If this is our situation and you need to select, then the software testing life cycle is your saviour. 

When to Use Both SDLC And STLC 

In short, they are not the competitors. In many projects, they work side by side. While developers work on building features (SDLC), testers prepare test cases and environments (STLC). If we break down the phase 

Then it'll be easy.

Times are changing, as well as the pattern. Modern software development, like DevOps and Agile methodologies, involves SDLC and STLC that are tightly integrated. 

Included:

• QA involvement begins from the requirement phase, not after coding.
• Developers and testers work in parallel sprints
• Regular testing makes sure each iteration is verified immediately

If you want to build a modern and well-polished software, then go for the software development life cycle method. A well-polished means well secured. Right? In that sense, you need to secure the software as well. If there is a bug, then it's not secure, and anyone can hack the system. So you need a testing team. For that, a proper STLC method needs to be applied. A perfect working software needs these two to work side by side to make an excellent product. Their working process may be different, but they are interconnected.

Final Note

Now we know the real difference between SDLC and STLC. Both are important components in the software development process without any doubt. While SDLC ensures that the software develops efficiently, STLC makes sure that the project is tested thoroughly to meet quality benchmarks.  If you are aware of building a proper world-class software or app, then SDLC and STLC both work as a framework to get the best result.

Together, they create a strong foundation for successful, high-quality, and user-centric software applications.

FAQs

What Is the Main Difference Between SDLC and STLC?

In short, SDLC is about “development”, and STLC is about “validation.”

What Comes First, SDLC or STLC ?

SDLC comes first. It starts when project requirements are gathered and continues through design and coding. STLC starts once the requirements are ready for testing preparation. 

Can SDLC and STLC Run Simultaneously?

Yes. In modern Agile and DevOps environments, SDLC and STLC run in parallel.

Why Is STLC Important in Software Development?

STLC ensures the software is bug-free, reliable, and user-friendly before it reaches customers.

Is Testing a Part of SDLC or STLC?

Testing is present in both SDLC and STLC. In SDLC, testing is one phase where the software is verified. In STLC, testing is the entire lifecycle

What Are the Major Stages of SDLC and STLC?

SDLC Phases 

Requirement Analysis → Design → Development → Testing → Deployment → Maintenance

STLC Phases

Requirement Analysis → Test Planning → Test Case Design → Environment Setup → Test Execution → Test Closure

Can a Project Succeed Without STLC?

No. Skipping STLC can result in undetected bugs, poor performance, or security issues.

How Does STLC Improve SDLC?

STLC complements SDLC by catching defects early, ensuring that every phase of development ensure quality standards. It provides feedback to developers, leading to continuous improvement and faster issue resolution.

Which Is More Important — SDLC or STLC?

Both are equally important. Without SDLC, there’s no product to test. Without STLC, the developed product could contain defects. Together, they ensure software that is functional, reliable, and high-quality.