11.2.1.2 analyze the advantages and disadvantages of waterfall, agile, and spiral models
 

Models of Software Development Life Cycle

When creating software, we go through several stages, we define these stages in the system development life cycle.

Software Development Life Cycle (SDLC) - a series of events that occur with the system in the process of its creation and further use.

There are many SDLC models, in middle school, you learn the most general model.

The Software Development Life Cycle (SDLC) is a structured process used by software development teams and organizations to design, develop, test, deploy, and maintain software systems or applications. It outlines the steps and stages that a software project goes through from its inception to its completion.

Key stages of the software development life cycle

The following are the key stages of the cycle:

Analysis.

This is the first step when the team decides what the software needs to do. The main point is to think about what the user will want from the program. At this stage, it might be a good idea to ask other people what they want from the software. Who is going to use it? What information do they need to input? What information or data does it need to output? Consider existing similar systems or determine how the current system works.

Design

The team works out the details of the program by breaking it down into smaller chunks. This includes thinking about the visual appearance and the programming behind the software. The team will use pseudocode and diagrams to work out how the program should go.

Implementation

The program code is written. Good pseudocode allows the implementation stage to be relatively easy. The code is normally written in a high-level language.

Testing

This involves testing the program under various conditions to make sure it is going to work. You need to think about what devices it could be used on and what might cause the program to crash.

Evaluation

The final stage of the SDLC discusses the level of achievement of the goals. The key evaluation criterion is the use of the system by the intended users.

Models of the software development life cycle

There are various SDLC models, but they typically share common phases, which may vary in name and number. 

Waterfall (Cascade) model

The Waterfall Model is a traditional and linear software development methodology that organizes the software development process into a sequence of discrete phases, with each phase dependent on the deliverables of the previous one. It is often represented as a waterfall, where progress flows in one direction, and each phase is completed before moving on to the next. Here are the key characteristics and phases of the Waterfall Model:

Phases of the Waterfall model

a. Requirements gathering and analysis:

In this initial phase, project stakeholders work closely to define and document the system's requirements comprehensively. This phase aims to establish a clear understanding of what the software must do and achieve.

b. System Design:

Once the requirements are well-defined, the system design phase begins. During this phase, system architects and designers create a detailed blueprint of how the software will be structured, including its architecture, database design, and user interface design.

c. Implementation/Development/Coding:

In this phase, developers write the actual code based on the system design specifications. The implementation phase involves translating the design into executable software and building all the necessary features and functionality.

d. Testing:

After coding is complete, the software is rigorously tested to identify and resolve defects or bugs. This phase includes various types of testing, such as unit testing, integration testing, and system testing, to ensure that the software works as intended.

e. Deployment (or Installation):

Once testing is successful, the software is deployed to a production environment or made available to end-users. This is when users can begin to interact with the software.

f. Maintenance and Support:

The final phase of the Waterfall Model involves ongoing maintenance and support of the software. This includes addressing any issues that arise, making updates, and ensuring the long-term reliability and stability of the system.

Advantages of the Waterfall model

• Sequential and structured. The Waterfall Model follows a linear and structured approach, which can make project management and tracking progress relatively straightforward.
• Clear documentation. Each phase produces well-documented artifacts, which can be useful for auditing, compliance, and future reference.
• Appropriate for well-defined projects. It works well when project requirements are stable, clear, and unlikely to change during development.
• Predictable timelines. It allows for accurate project timelines and cost estimates if requirements are well-understood.

Disadvantages of the Waterfall mode

• Inflexibility to change. The Waterfall Model is not adaptable to changing requirements, making it unsuitable for projects where requirements may evolve.
• Late user involvement. Users typically do not see the software until late in the development process, which can lead to misunderstandings and dissatisfaction.
• High risk. If requirements are misunderstood or incorrectly documented at the beginning, it can result in costly rework.
• Long delivery time. The approach can lead to long delivery times, especially for complex projects.

The Waterfall Model is most appropriate when the following conditions are met:

• Well-known, clear, and fixed requirements. The Waterfall Model is best suited for projects where the requirements are thoroughly understood, well-documented, and unlikely to change significantly throughout the project's lifecycle. Any changes in requirements can be costly and disruptive in a Waterfall approach.
• Stable product definition. The project should have a stable and clearly defined product or system concept from the outset. This means that the project scope and objectives should remain relatively unchanged throughout the development process.
• Technology understanding. The technology stack and tools to be used in the project should be well-known and understood by the development team. This includes having experience with the programming languages, frameworks, and platforms that will be used.
• No ambiguous requirements. There should be no ambiguity or uncertainty in the project's requirements. All stakeholders should have a common understanding of what the final product should be, leaving no room for interpretation or subjective judgment.
• Ample resources with the required expertise. Sufficient resources, including skilled personnel, should be available and dedicated to the project. The team should possess the necessary expertise to execute the project successfully.
• Short project duration. The Waterfall Model is more suitable for shorter projects with well-defined goals and requirements. For longer projects, the risk of changing requirements and evolving technologies over time increases, making other methodologies like Agile more appropriate.

Agile model

The Agile Model, or Agile methodology, is a modern and flexible approach to software development and project management. It emphasizes collaboration, customer feedback, and the iterative delivery of small, working increments of a software product. Agile methodologies are particularly well-suited for projects where requirements are subject to change, and where the ability to adapt quickly is crucial. 

Requirements (User Stories/Backlog):

Agile projects begin with the identification and prioritization of requirements, often expressed as user stories or items in a product backlog. These requirements are typically short, concise, and focused on user needs.

Design (Sprint Planning):

In Agile, design activities are often integrated into the sprint planning phase. During sprint planning, the development team discusses how they will implement the selected user stories or backlog items in the upcoming sprint. Design decisions are made as part of this planning process.

Development (Sprint):

The development phase in Agile is carried out in iterations called sprints. During a sprint, the development team works on implementing the user stories or backlog items selected for that sprint. This phase involves coding, testing, and integration of the features.

Test (Continuous Testing):

Testing is a continuous activity throughout the Agile development process. Agile teams conduct testing alongside development to ensure that each user story or feature is tested as it is built. Automated testing is often used to support continuous testing practices.

Deploy (Incremental Delivery):

Agile promotes incremental delivery, meaning that working software is deployed or released incrementally throughout the project. At the end of each sprint, there is typically a potentially shippable product increment that can be deployed if the product owner chooses to do so.

Review (Sprint Review/Retrospective):

The Agile model includes regular review and reflection phases. At the end of each sprint, a Sprint Review is conducted to demonstrate the completed work to stakeholders and gather feedback. Additionally, a Sprint Retrospective is held to reflect on the sprint process and identify areas for improvement.

Advantages of the Agile model

• Customer-centric. Focuses on customer collaboration and meeting user needs.
• Flexibility. Adaptable to changing requirements and priorities.
• Frequent value delivery. Provides working increments of the product regularly.
• Quality. Emphasizes continuous testing and early issue identification.
• Transparency. Offers clear project visibility through various ceremonies.
• Empowered Teams. Encourages self-organizing, cross-functional teams.
• Rapid Feedback. Enables quick problem-solving and process improvement.
• Risk Mitigation. Divide projects into manageable iterations to reduce risks.
• Efficient Resource Allocation. Optimizes resource utilization for value delivery.
• Continuous Improvement. Fosters a culture of ongoing process enhancement.

Disadvantages of the Agile model

• Complexity for large projects. Agile may face challenges when applied to large, complex projects.
• Limited documentation. Agile often produces less comprehensive documentation, which can be a concern for certain industries or regulatory requirements.
• Requires active customer involvement: Continuous customer involvement may be demanding for some projects.
• Scope creep. Agile's flexibility can lead to scope creep if not managed effectively.
• Team skill requirements. Agile teams need strong communication and collaboration skills.
• Uncertain timelines. Predicting exact project timelines can be challenging due to changing requirements.
• Resource intensive. Frequent meetings and collaboration can be resource-intensive.
• Not suitable for all projects. Agile may not be ideal for projects with highly stable, well-defined requirements.

Spiral model

The Spiral Model is a software development methodology that combines elements of iterative development and risk management. It was developed by Barry Boehm in the 1980s and is particularly well-suited for projects with a high level of uncertainty and risk. The Spiral Model is characterized by its iterative approach, where the project progresses through a series of cycles, or "spirals," each of which includes the following key phases:

Planning:

In the initial phase, project objectives, requirements, constraints, and risks are identified and defined. A preliminary project plan is developed, outlining the overall strategy and approach for the project.

Risk Analysis:

This phase focuses on identifying and assessing project risks. Risk analysis involves evaluating potential technical, schedule, and cost risks associated with the project. Risks are prioritized based on their potential impact and likelihood.

Engineering (Development):

Once the risks have been assessed, the development team works on creating a version of the product based on the requirements and addressing the highest-priority risks. This phase can be viewed as a mini-waterfall or iterative process within each spiral.

Evaluation (Testing):

After the product increment is developed, it undergoes testing and evaluation. This phase includes quality assurance activities to ensure that the product meets the specified requirements and that identified risks have been mitigated.

Review and Planning:

In this phase, the project is reviewed with stakeholders to assess progress, reevaluate risks, and make decisions about whether to proceed to the next spiral. Based on the feedback and results, the project plan is refined and updated.

Advantages of the Spiral model

• Risk management. The model places a strong emphasis on identifying and addressing risks early in the project, which helps in managing and mitigating potential issues.
• Flexibility. The iterative nature of the model allows for changes to be incorporated into the project at any stage, making it suitable for projects with evolving requirements.
• Client involvement. Stakeholder involvement is encouraged at each spiral, ensuring that client feedback is continuously incorporated into the project.
• Quality focus. Testing and quality assurance are integral to each spiral, resulting in a focus on product quality and reliability.

Disadvantages of the Spiral model

• Complexity. The model's iterative nature can make it more complex to manage compared to linear models like the Waterfall.
• Resource Intensive. The risk analysis and evaluation phases can be resource-intensive, requiring significant time and effort.
• Uncertain Timelines. Predicting the exact timeline and number of spirals for project completion can be challenging.
• Not Suitable for Small Projects. The model's overhead may not be justified for small or straightforward projects.
• Documentation. While it emphasizes documentation, the level of documentation may vary depending on project needs and can sometimes be less extensive than in more traditional models.

Any system development lifecycle must result in a high-quality system that meets or exceeds customer expectations, is completed within time and cost, is efficient and effective, is inexpensive to maintain, and is cost-effective to improve.

Questions:

1. What is the Waterfall model in software development?
2. What is the Agile model and how does it differ from Waterfall?
3. What is the Spiral model and how does it integrate risk management?
4. In which types of projects is the Waterfall model most appropriate?
5. When should the Agile model be used in software development?
6. What types of projects benefit from the Spiral model?
7. How does the Waterfall model handle project changes?
8. What are the main advantages of using the Agile model?
9. What are the key phases of the Spiral model?
10. What are the key differences between Waterfall and Spiral models?

Exercises:

Ex. 1 

Ex. 2

Ex. 3

Ex. 4

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