WHAT IS SOFTWARE DEVELOPMENT MODELS?

• Software Development life cycle (SDLC) is a spiritual model used in project management that defines the stages include in an information system development project, from an initial feasibility study to the maintenance of the completed application.
• There are different software development life cycle models specify and design, which are followed during the software development phase. These models are also called "Software Development Process Models." Each process model follows a series of phase unique to its type to ensure success in the step of software development.

WATERFALL MODEL

• The Waterfall Model is a classical software development methodology. It was first introduced by Winston W. Royce in 1970.
• The waterfall model is a software development model used in the context of large, complex projects, typically in the field of information technology. It is characterized by a structured, sequential approach to project management and software development.
• It is a linear and sequential approach to software development that consists of several phases. It must be completed in a specific order.

• Following are the features of the waterfall model:

  1. Sequential Approach: The waterfall model involves a sequential approach to software development, where each phase of the project is completed before moving on to the next one.
  2. Document-Driven: The waterfall model depended on documentation to ensure that the project is well-defined and the project team is working towards a clear set of goals.
  3. Quality Control: The waterfall model places a high emphasis on quality control and testing at each phase of the project, to ensure that the final product meets the requirements and expectations of the stakeholders.
  4. Rigorous Planning: The waterfall model involves a careful planning process, where the project scope, timelines, and deliverables are carefully defined and monitored throughout the project lifecycle.

• Here are some cases where the use of the Waterfall Model is best suited:

  • Well-understood Requirements: Before beginning development, there are precise, reliable, and thoroughly documented requirements available.
  • Very Little Changes Expected: During development, very little adjustments or expansions to the project’s scope are anticipated.
  • Small to Medium-Sized Projects: Ideal for more manageable projects with a clear development path and little complexity.
  • Predictable: Projects that are predictable, low-risk, and able to be addressed early in the development life cycle are those that have known, controllable risks.

PHASES OF WATERFALL MODEL:

• The Waterfall Model has six phases which are:

  1. Requirements: The first phase involves gathering requirements from stakeholders and analyzing them to understand the scope and objectives of the project.
  2. Design: Once the requirements are understood, the design phase begins. This involves creating a detailed design document that outlines the software architecture, user interface, and system components.
  3. Development: The Development phase include implementation involves coding the software based on the design specifications. This phase also includes unit testing to ensure that each component of the software is working as expected.
  4. Testing: In the testing phase, the software is tested as a whole to ensure that it meets the requirements and is free from defects.
  5. Deployment: Once the software has been tested and approved, it is deployed to the production environment.
  6. Maintenance: The final phase of the Waterfall Model is maintenance, which involves fixing any issues that arise after the software has been deployed and ensuring that it continues to meet the requirements over time.
• The classical waterfall model divides the life cycle into a set of phases. This model considers that one phase can be started after the completion of the previous phase. That is the output of one phase will be the input to the next phase. Thus the development process can be considered as a sequential flow in the waterfall. Here the phases do not overlap with each other. 

V-MODEL

• The V-model is a type of SDLC model where the process executes sequentially in a V-shape. It is also known as the Verification and Validation model. It is based on the association of a testing phase for each corresponding development stage. 
• The development of each step is directly associated with the testing phase. The next phase starts only after completion of the previous phase i.e., for each development activity, there is a testing activity corresponding to it. 
•  It is based on the idea of a “V” shape, with the two legs of the “V” representing the progression of the software development process from requirement gatherings and analysis to design, implementation, testing, and maintenance.
• This is a highly disciplined model and Phases are completed one at a time.
• This model focuses on verification and validation activities early in the life cycle thereby enhancing the probability of building an error-free and good quality product.

V-MODEL DESIGN:

• Requirement Gathering and Analysis: The first phase of the V-Model is the requirements gathering and analysis phase, where the customer’s requirements for the software are gathered and analyzed to determine the scope of the project.
• Design: In the design phase, the software architecture and design are developed, including the high-level design and detailed design.
• Implementation: In the implementation phase, the software is built based on the design.
• Testing: In the testing phase, the software is tested to ensure that it meets the customer’s requirements and is of high quality.
• Deployment: In the deployment phase, the software is deployed and put into use.
• Maintenance: In the maintenance phase, the software is maintained to ensure that it continues to meet the customer’s needs and expectations.
• The V-Model is often used in safety: critical systems, such as aerospace and defence systems, because of its emphasis on thorough testing and its ability to clearly define the steps involved in the software development process.

WHEN TO USE V-MODEL?

• Raceability of Requirements: The V-Model proves beneficial in situations when it’s imperative to create precise traceability between the requirements and their related test cases.
• Complex Projects: The V-Model offers a methodical way to manage testing activities and reduce risks related to integration and interface problems for projects with a high level of complexity and interdependencies among system components.
• Waterfall-Like Projects: Since the V-Model offers an approachable structure for organizing, carrying out, and monitoring testing activities at every level of development, it is appropriate for projects that use a sequential approach to development, much like the waterfall model.
• Safety-Critical Systems: These systems are used in the aerospace, automotive, and healthcare industries. They place a strong emphasis on rigid verification and validation procedures, which help to guarantee that essential system requirements are fulfilled and that possible risks are found and eliminated early in the development process.

PROTOTYPE MODEL

• Prototype model is an activity in which prototypes of software applications are created. First a prototype is created and then the final product is manufactured based on that prototype.
• The prototype model was developed to overcome the shortcomings of the waterfall model. 
• This model is created when we do not know the requirements well.
• This model is used when the customers do not know the exact project requirements beforehand. In this model, a prototype of the end product is first developed, tested, and refined as per customer feedback repeatedly till a final acceptable prototype is achieved which forms the basis for developing the final product. 
• Prototype Model is suggested to create applications whose prototype is very easy and which always includes human machine interaction within it.

STEPS OF PROTOTYPE MODEL:

• Step 1: Requirement Gathering and Analysis: This is the initial step in designing a prototype model. In this phase, users are asked about what they expect or what they want from the system.

• Step 2: Quick Design: This is the second step in the Prototyping Model. This model covers the basic design of the requirement through which a quick overview can be easily described.
• Step 3: Build a Prototype: This step helps in building an actual prototype from the knowledge gained from prototype design
• Step 4: Initial User Evaluation: This step describes the preliminary testing where the investigation of the performance model occurs, as the customer will tell the strengths and weaknesses of the design, which was sent to the developer.
• Step 5: Refining Prototype: If any feedback is given by the user, then improving the client’s response to feedback and suggestions, the final system is approved.
• Step 6: Implement Product and Maintain: This is the final step in the phase of the Prototyping Model where the final system is tested and distributed to production, here the program is run regularly to prevent failures.

RAD MODEL

• The RAD model or Rapid Application Development model is a type of software development methodology that emphasizes quick and iterative release cycles, primarily focusing on delivering working software in shorter timelines. 
• Unlike traditional models such as the Waterfall model, RAD is designed to be more flexible and responsive to user feedback and changing requirements throughout the development process.
• IBM first proposed the Rapid Application Development or RAD Model in the 1980s. The RAD model is a type of incremental process model in which there is a concise development cycle. The RAD model is used when the requirements are fully understood and the component-based construction approach is adopted.
• The main objective of RAD model is to reuse code, components, tools, processes in project development.

PHASES OF RAD MODEL:

• This model consists of 4 basic phases:

  1. Requirements Planning – This involves the use of various techniques used in requirements elicitation like brainstorming, task analysis, form analysis, user scenarios, FAST (Facilitated Application Development Technique), etc. It also consists of the entire structured plan describing the critical data, methods to obtain it, and then processing it to form a final refined model.
  2. User Description – This phase consists of taking user feedback and building the prototype using developer tools. In other words, it includes re-examination and validation of the data collected in the first phase. The dataset attributes are also identified and elucidated in this phase.
  3. Construction – In this phase, refinement of the prototype and delivery takes place. It includes the actual use of powerful automated tools to transform processes and data models into the final working product. All the required modifications and enhancements are to be done in this phase.
  4. Cutover – All the interfaces between the independent modules developed by separate teams have to be tested properly. The use of powerfully automated tools and subparts makes testing easier. This is followed by acceptance testing by the user.

WHEN TO USE RAD MODEL?

• Well-understood Requirements: When project requirements are stable and transparent, RAD is appropriate.
• Time-sensitive Projects: Suitable for projects that need to be developed and delivered quickly due to tight deadlines.
• Small to Medium-Sized Projects: Better suited for smaller initiatives requiring a controllable number of team members.
• High User Involvement: Fits where ongoing input and interaction from users are essential.
• Innovation and Creativity: Helpful for tasks requiring creative inquiry and innovation.
• Prototyping: It is necessary when developing and improving prototypes is a key component of the development process.
• Low technological Complexity: Suitable for tasks using comparatively straightforward technological specifications.

SPIRAL MODEL

• Spiral model is a Software development process model. This model has characteristics of both iterative and waterfall models. This model is used in projects which are large and complex. 
• This model was named spiral because if we look at its figure, it looks like a spiral, in which a long curved line starts from the center point and makes many loops around it. The number of loops in the spiral is not decided in advance but it depends on the size of the project and the changing requirements of the user.
• The Spiral model is called a Meta Model because it subsumes all the other SDLC models. 

• The Spiral Model is a risk-driven model, meaning that the focus is on managing risk through multiple iterations of the software development process. It consists of the following phases:

  1. Objectives Defined: In first phase of the spiral model we clarify what the project aims to achieve, including functional and non-functional requirements.
  2. Risk Analysis: In the risk analysis phase, the risks associated with the project are identified and evaluated.
  3. Engineering: In the engineering phase, the software is developed based on the requirements gathered in the previous iteration.
  4. Evaluation: In the evaluation phase, the software is evaluated to determine if it meets the customer’s requirements and if it is of high quality.
  5. Planning: The next iteration of the spiral begins with a new planning phase, based on the results of the evaluation.

RISK HANDLING IN SPIRAL MODEL:

• A risk is any adverse situation that might affect the successful completion of a software project. The most important feature of the spiral model is handling these unknown risks after the project has started. Such risk resolutions are easier done by developing a prototype.

  1. The spiral model supports coping with risks by providing the scope to build a prototype at every phase of software development. 
  2. The Prototype Model also supports risk handling, but the risks must be identified completely before the start of the development work of the project.
  3. But in real life, project risk may occur after the development work starts, in that case, we cannot use the Prototyping Model.
  4. In each phase of the Spiral Model, the features of the product dated and analyzed, and the risks at that point in time are identified and are resolved through prototyping.
  5. Thus, this model is much more flexible compared to other SDLC models. 

EXAMPLE OF SPIRAL MODEL:

• Real-Life Example of Spiral Model: Developing an E-Commerce Website

  • First Spiral – Planning and Requirements: The initial phase involves gathering basic requirements for the e-commerce website, like product listing, shopping cart, and payment options. The team analyzes any risks, such as security or scalability, and creates a small prototype.
    • Example: The team builds a simple homepage with a basic product catalog to see how users interact with it and identify any design flaws.
  • Second Spiral – Risk Analysis and Refining the Design: After gathering feedback from the prototype, the next spiral focuses on adding more features and fixing early issues. The team addresses security risks, such as secure payment processing, and tests how well the site handles increasing user traffic. 
    • Example: A basic shopping cart and user registration system are added. The payment system is also tested with dummy transactions to ensure security. 
      • Third Spiral – Detailed Implementation: With more feedback, the team further refines the design, adding advanced features like order tracking, customer reviews, and search functionality. Risks like scalability (handling many users) are re-evaluated, and more testing is conducted.
        • Example: The website now supports user profiles, product reviews, and real-time inventory updates. The team tests how the system handles large volumes of orders during peak times.
      • Final Spiral – Full Deployment: The final phase involves full implementation, thorough testing, and launching the e-commerce website to the public. Ongoing risks like system crashes or user feedback are monitored and addressed as needed.
        • Example: The website goes live with all features, including secure payments, product listings, and order tracking, ready for users to shop online.

AGILE MODEL

• The Agile Model was primarily designed to help a project adapt quickly to change requests. So, the main aim of the Agile model is to facilitate quick project completion. To accomplish this task, agility is required.
• In earlier times, iterative waterfall model was used to create software. But in today's time developers have to face many problems. The biggest problem is that in the middle of software development, the customer asks to make changes in the software. It takes a lot of time and money to make these changes, so Agile Model is proposed.

STEPS IN AGILE MODEL:

• Requirement Gathering:- In this step, the development team must gather the requirements, by interaction with the customer. development team should plan the time and effort needed to build the project. Based on this information you can evaluate technical and economical feasibility.
• Design the Requirements:- In this step, the development team will use user-flow-diagram or high-level UML diagrams to show the working of the new features and show how they will apply to the existing software. Wireframing and designing user interfaces are done in this phase.
• Construction / Iteration:- In this step, development team members start working on their project, which aims to deploy a working product.
• Testing / Quality Assurance:- Testing involves Unit testing, Integration testing, and System testing. A brief introduction of these three tests is as follows:
  • Unit Testing:- Unit testing is the process of checking small pieces of code to ensure that the individual parts of a program work properly on their own. Unit testing is used to test individual blocks (units) of code.
  • Integration Testing:- Integration testing is used to identify and resolve any issues that may arise when different units of the software are combined.
  • System Testing:- Goal is to ensure that the software meets the requirements of the users and that it works correctly in all possible scenarios.
• Deployment:- In this step, the development team will deploy the working project to end users.
• Feedback:- This is the last step of the Agile Model. In this, the team receives feedback about the product and works on correcting bugs based on feedback provided by the customer.

INCREMENTAL PROCESS MODEL

• In Incremental Model, the software development process is divided into several increments and the same phases are followed in each increment. In simple language, under this model a complex project is developed in many modules or builds.
• For example, we collect the customer's requirements, now instead of making the entire software at once, we first take some requirements and based on them create a module or function of the software and deliver it to the customer. Then we take some more requirements and based on them add another module to that software.

PHASES OF INCREMENTAL MODEL:

• Requirement analysis: In Requirement Analysis At any time, the plan is made just for the next increment and not for any kind of long-term plan. Therefore, it is easier to modify the version as per the needs of the customer.
• Design & Development: At any time, the plan is made just for the next increment and not for any kind of long-term plan. Therefore, it is easier to modify the version as per the needs of the customer. The Development Team first undertakes to develop core features (these do not need services from other features) of the system. Once the core features are fully developed, then these are refined to increase levels of capabilities by adding new functions in Successive versions. Each incremental version is usually developed using an iterative waterfall model of development. 
• Deployment and Testing: After Requirements gathering and specification, requirements are then split into several different versions starting with version 1, in each successive increment, the next version is constructed and then deployed at the customer site. in development and Testing the product is checked and tested for the actual process of the model.
• Implementation: In implementation After the last version (version n), it is now deployed at the client site.