Models of Software Development Life Cycle

Last Updated on 2 years by Touhid

Software development life cycle (SDLC) is an organized methodology that defines required activities in software development project. There are different models of software development life cycle to develop a software. The main aim of SDLC is to develop quality based software and ensures the quality of the software according to customer requirements. In this post, we will discuss on different models of software development life cycle with their advantages and disadvantages.

Models of Software Development Life Cycle

Software Development Life Cycle or SDLC is a software development framework that defines required steps to develop standard and quality based software. The models of software development life cycle are very much important to develop a software or application. It meets the client’s requirements, ensure correctness and timely delivery to the client. The SDLC consists of different phases to develop a software or application, which are as follows:

• Requirement analysis
• Planning
• Design
• Development
• Testing
• Deployment and
• Maintenance

A software development life cycle model is processes that are being selected before software development. There are different models of software development life cycle, which are as follows:

1. Waterfall model
2. Iterative model
3. Spiral model
4. V-shaped model
5. Agile model

Now, we will discuss each type models of software development life cycle with their advantages and disadvantages.

1. Waterfall Software Development Model

Waterfall model is the models of software development life cycle, where software development process is divided into different phases. The output of one phase works as input for the next phase. The development of next phase starts only when the previous phase is complete.

The Waterfall model is also known as the linear sequential model. There are six sequential phases in Waterfall model, which are as follows:

1. Requirement analysis
2. Design
3. Development
4. Testing
5. Deployment and
6. Maintenance

1. Requirement Analysis

Requirement analysis is the first phase of Waterfall software development life cycle which define the system inputs, processes, outputs and interfaces. In this phase, all the possible business requirements are gathered and documented in a software requirement specification (SRS).

2. Design

The software requirement specifications are studied in this phase and system design is prepared based on that requirements. It specifies the required hardware, system requirements and overall system architecture of the software .

This system design phase covers the technical design requirements such as programming language, database, services, and high-level technical details of the project. Finally the work is documented as a Software Design Document (SDD).

3. Development

In this phase, system design is converted into source code using any suitable programming language. Here, each module of the software is developed and checks whether the module is working correctly or not (Unit Testing).

4. Testing and Integration

Testing and Integration phase is very important phase of software development life cycle which ensure the quality and efficiency of the software. When the development of each module has done, then all modules are integrated into a system following the testing process.

Here, each module is tested for their interactions with each other module. The system testing consists of different types of testing activities such as alpha testing, beta testing and acceptance testing. This phase perform all the testing activities to make sure that the system meets the software requirements specification.

5. Deployment

Now, it is time to deliver the software to the customer. Once the functional and nonfunctional testing is done and there has no error, the software is deployed in the customer hosting environment. It will ensure that the software is up and running in the customer environment.

6. Maintenance

It is another important phase of software development life cycle. This phase will start when the software has been delivered, installed, and operational in the customer environment.

During this phase, if the software not run properly or found any problem, the developer shall fix the problem and the updated in server. Developer also enhances the software with more features and released better versions to improve the software quality.

A. Advantages of Waterfall Model

The advantages of Waterfall model are as follows –

• It allows departmentalization and control
• It is very simple and easy to understand
• Easy to manage and use
• It is suitable for small projects where requirements are easy to understood
• Each phase has specific deliverable
• Each phase is clearly well defined.
• Easy to arrange tasks.
• Process and results are well documented.

B. Disadvantages of Waterfall Model

The main disadvantage of Waterfall model is that it is time consuming process and very difficult to go back in the previous stage. However, the other disadvantages of the Waterfall  model are as follows –

• Its provide low flexibility
• Difficult to measure progress within stages
• Very difficult to estimate time and cost
• It is very difficult to go back previous phase
• Not suitable for long and ongoing projects.
• Requirements changing is very difficult while developing.
• Not a good quality model for complex and object-oriented application.
• It is also not suitable for the projects where requirements are high risk of changing.

If someone ask me, which model is the best for software development? My answer will be the best models of software development life cycle is waterfall model if the project size is small.

Iterative Development Model

The Iterative model is also called an incremental model which has designed to improve the existing waterfall model. This model is almost same as the previous waterfall model except few changes are made to increase the effectiveness of the software development.

There are several phases of Iterative Model such as planning, design, implementation, testing, deployment, review and maintenance phase.

Once the initial requirement planning process is completed, the other phases are repeated to make new versions of the software for every cycle. The requirements are included, designed, coded, tested and added to the software on each iteration.

1. Planning 

This is the first stage of the iterative model, where the system related information is gathered from customers and analyzed. Then, proper planning is done after collecting the requirements.

2. Design 

In the design phase of iterative software development model, the developer team designs the different diagrams of software such as data flow diagram (DFD), activity diagram, class diagram and state transition diagram.

This design phase covers the technical design requirements such as programming language, database models, business logic and high-level technical details of the project.

3. Implementation

The third and the most important phase of the iterative model is software implementation. In the implementation phase, the planning, specification, and design phases are transformed into source code. Here, each module of the software is developed and checks whether the module is working correctly or not (Unit Testing).

4. Testing 

After completion the implementing phase, the software starts for testing using different testing methods. In this phase, each module of the software is tested for their interactions with other module. The system testing consists of different types of testing activities such as alpha testing, beta testing and acceptance testing.

This testing stage allows user to identify any potential bugs and make sure that the system meets the software requirements specification.

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5. Deployment

Once the testing is done and the software is deployed in the customer hosting environment.

6. Review

When the software is deployed in the customer environment, review phase checked as per the current requirements. If there found any error or need to change any requirements then the process starts for next iteration.

A. Advantage of Iterative Model

The advantages of iterative model are as follows:

• Software can be developed quickly
• To change the software requirements is more cost effective.
• It is more flexible to change the software scope and requirements.
• Each iteration is easily managed.
• Risks are identified on each iteration and resolved during next iteration.
• It takes corrective action in a limited financial plan.
• Results are obtained early and periodically.

B. Disadvantage of Iterative Model

The disadvantages of iterative development model are as follows:

• It requires more resources.
• Although changing the software requirements are cost effective, but it is not suitable for changing the requirements.
• It also requires more management and high skilled resources for risk analysis.
• The Iterative Model is ineffective for small project.
• Finally, project ending date is not confirmed because of changing the requirements.

Spiral Model

Spiral model is another models of software development life cycle which is combination of iterative model and waterfall model. The Spiral model is used for large projects. It is based on the risk driven process model where project’s success depends on the risk analysis phase.

Spiral model, generally consists of four different phases such as planning, risk analysis, engineering and evaluation. These phases are followed repeatedly, in each round, until no further requirements are needed to be implemented in the final products.

1. Planning 

Planning is the first phase of the software development life cycle (spiral model), where the business and system related information is gathered from customers and analyzed. Then, proper planning is done after collecting the requirements.

The planning phase includes the estimating cost of the project, schedule and resources for the iteration.

2. Risk Analysis

In the spiral model, the Risk Analysis phase identifying, estimating and monitoring the technical feasibility, management risks and find out alternate solutions of the project. If any risk is found during the risk analysis then necessary steps are taken to reduce the risks and alternate solutions are implemented.

However, a standard prototype is developed at the end of the risk analysis phase.

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3. Engineering

When the planning and risk analysis phase finalized then the engineering phase will start for developing the software. In the engineering phase, software is developed, tested and deployed in the customer environment.

4. Evaluation 

This is the last phase of spiral model. In this phase, customers evaluate the output of the project and provide feedback also revert if any changes required. The evaluation phase includes all the above phases, where customer goes through each phase for evaluating the software.  At last, the project continues to the next spiral or iteration.

A. Advantages of Spiral model

The advantages of Spiral development life cycle are as follows:

• This model is useful for large projects
• It provides Flexibility to change the requirements
• Software development is very fast
• It provides strong approval and documentation.
• The features are added in a systematic way.
• The spiral model facilitates risk management

B. Disadvantages of Spiral model

The disadvantages of Spiral model are as follows:

• It requires expert people to identify risk of the project.
• Project completion date may not be known early
• It is not suitable for smaller projects
• The spiral model is costly to develop a project
• It is more complex than other model

V-Shaped Software Model

V- Shaped model is a models of software development life cycle which directly includes a set of verification and validation steps for every single phase in the development cycle.

It is an extension of the waterfall model and it is also known as Verification and Validation model. The process of V-model is in a sequential manner that means next phase starts only after completion of the previous phase.

A. Verification

Verification is the process of evaluation, where requirements specification and design meet for software development. There are several Verification phases in the V-Model, which are described as follows:

1. Requirement Analysis

Requirement analysis is the first Verification phases in the V-Model, where all possible business and system requirements are gathered. This is very important phase of software development life cycle because most of the customers do not what exactly they desire. In requirements analysis phase, acceptance tests are designed which to be implemented later during software testing phases.

2. System Design

In this phase, software requirement specifications (SRS) are studied and prepared system design based on the requirements. This system design phase covers the technical design requirements such as programming language, database and services. During this phase, system tests are designed for later use of testing phases.

 3. Architectural Design

The architectural design consists of modules, their functionalities, interfaces, database relationships, architecture diagrams and technology details. It is also referred to as High Level Design (HLD), which creating a blueprint for the hardware, software and network diagram of the system.

The high-level design focuses on overall system architecture and design which provide overview of solution, platform, service, and process. An Integration test plan is developed in this phase to test the ability of software.

4. Module Design

In the module design phase, the high level design is broken down into small modules and programs, where the internal design for each module is specified. It is also referred to as Low-Level Design (LLD), which defines the business logic for each and every component of the system.

Module design is important because the design is compatible with the other modules and external systems. The unit test is designed during this phase to eliminate the faults and errors at early stage.

5. Coding 

Coding Phase is the last and bottom of the V-Shape model. In this phase, modules design is converted into source code using any suitable programming language based on the coding guidelines and standards. The coding is done by software developer or programmers.

Here, each module of the software is developed and testing is performed by the developers to check whether the module is working correctly or not.

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B. Validation

Validation is the process of evaluation the software (after the completion of the development phase) in order to determine whether software meets the customer requirements.

The validation phases in a V-Model are as follows.

1. Unit Testing

In the V-shaped Model, the Unit Test Plans (UTPs) are designed during the module design phase. These UTPs are executed at code level and ensuring that all potential bugs or errors are removed at early stage.

2. Integration testing

The integration testing is developed during the architecture design phase. Here, the modules are integrated and ensure that all modules and architectural designs are correct. In integration testing, system is tested by verifying the communication between all modules within the system after adding any new functions.

3. System Testing

System testing is associated with the system design phase of V-model. The System testing test the complete application such as functional and non-functional requirements, inter dependency, communication and performance testing of the application.

4. User Acceptance Testing (UAT)

The final testing phase of V-model is acceptance testing, which is designed at requirement analysis phase. The user acceptance testing is performed in a user environment. It ensures that delivered system meets customer’s requirement and system is ready for deployment in customer environment.

A. Advantages of V-Shaped Model

The advantages of the V-Model are as follows −

• The V-Model is simple and easy to use.
• It is highly discipline model
• The model is easy to manage
• This model improves the reliability and quality of the software.
• Each phase has specific output and a review system.
• It is suitable for small projects where requirements are easily understood.

B. Disadvantages of V-Shaped Model

The disadvantages of the V-Model are as follows-

• The model does not provide flexibility to changes the requirements
• It is not a good quality model for complex and object-oriented projects.
• It is very expensive to changes the requirements

Agile Software Development Model

Agile model is the models of software development life cycle which is combination of the Iterative and Incremental model. The agile model focuses on the flexibility while developing a software. The main aim of the Agile Model is to complete the project very quickly and improve the quality of an application. In this model, the application is broken into small incremental builds and the builds are given in iterations.

The time duration for each iteration is near about one to three weeks. Every iteration involves cross functional teams working through a full software development life cycle including:

1. Planning
2. Requirements Analysis
3. Design
4. Coding
5. Unit Testing and
6. User Acceptance Testing (UAT)

The product is displayed to the customers for their feedback after end of the iteration. Customer’s feedback is playing an important role in software development life cycle because their feedback will be helpful for next iteration.

The feedback will also ensure that the features meet their requirements. To minimize the risk of the application testing is done on every development iteration.

A. Advantages of Agile Model

The advantages of the agile model are as follows –

• This model is realistic approach to software development.
• It requires minimum resources
• This model provides flexibility to developers.
• Easy to manage
• Customers can change their requirements at any stage.

B. Disadvantages of Agile Model

The disadvantages of the agile model are as follows –

• It is not work for small projects.
• It requires expert persons to take important decisions in the meeting
• Cost is slightly more as compared to waterfall or interactive model.
• If the project manager is not clear about the requirements then the project can go out off way.

Importance of Software Development Life Cycle 

The models of software development life cycle are very much important to develop a software or application. The main importance of software development process is that it provides full control of the software development and also ensures that the developed software meets the customer’s requirements.

However, the others importance’s models of SDLC are as follows:

• The SDLC model provides a standard framework to develop software.
• It provides goals and deliverable of the software.
• Customer requirements are find out at early stage.
• To find out the bugs and errors in the software before implementation.
• It ensures that the software will be timely delivery to the customer.
• SDLC model provides a guideline to develop a software.
• It ensures the security of the software.

Learn more about Cyber Security threats.

Best Models of Software Development Life Cycle

What are the best models of software development life cycle? Actually, it depends on the different factors of the project such as project requirements, size of the project, software developers, business environment, time and cost. Already we have discussed different models of software development life cycle such as waterfall model, agile model, V-shaped model, Spiral Model.

Waterfall model is the best models of software development life cycle if the project size is small, where the requirements of the software are fixed, easy to collect and the organization has experience of related projects.

On the other hand, agile model is the best model of software development process if the project size is large, where clients can change their requirements at any stage of the software development process even if the initial planning phase has been completed.

This agile method allows more flexibility than traditional methods, it reduces the risks, saves the time and cost of the software development.

Conclusion

Finally, We have discussed different models of software development life cycle with their advantages and disadvantages and also mention the importance of software development life cycle. Hope the article “models of software development life cycle” will be helpful, who want to develop software !!!