# **Software Development Life Cycle (SDLC)** The Software Development Life Cycle (SDLC) is a structured process used by the software industry to design, develop, and test high-quality software. It aims to produce a high-quality system that meets or exceeds customer expectations, reaches completion within times and cost estimates, and is effectively maintainable. ## **1.4.1 Different Phases of SDLC** The SDLC consists of a series of well-defined phases or steps. While the exact number and naming can vary, a comprehensive model includes the following: 1. **Defining the Problem Phase:** The initial step where the problem to be solved or the system to be developed is clearly defined. All product requirements are documented and approved. 2. **Planning Phase:** The project's goals are identified, and requirements are assessed. This includes a thorough evaluation of resources, personnel, costs, and the creation of a comprehensive project plan for management approval. 3. **Feasibility Study Phase:** This phase determines the viability and practicality of the proposed system by evaluating it across several dimensions. * ***Technical Feasibility:*** Assesses if the necessary technology (hardware, software, tools) is available to build the system. * ***Economic Feasibility:*** Evaluates the financial viability by comparing the project's costs and benefits. * ***Operational Feasibility:*** Assesses how well the proposed system aligns with the organization's current operational processes and goals. * ***Legal Feasibility:*** Checks if the proposed system complies with all applicable laws and regulations. * ***Schedule Feasibility:*** Determines if the project can be completed within the specified timeframe. 4. **Analysis Phase:** The project team determines the end-user requirements, often through client focus groups. The team analyzes the existing system to understand its functions and decides if the new project is justified with the available resources. 5. **Requirement Engineering Phase:** This crucial phase focuses on gathering, analyzing, documenting, and managing the system's requirements to ensure it meets stakeholder expectations. The output of this phase is the Software Requirement Specification (SRS) document. * ***Requirement Gathering:*** The process of identifying and documenting the needs of stakeholders. Common techniques include: * *Interviews:* Direct conversations with stakeholders. * *Surveys and Questionnaires:* Collecting information from a large number of people. * *Observation:* Watching users in their work environment to understand current processes. * *Document Analysis:* Reviewing existing documentation, reports, and manuals. * ***Requirement Validation:*** Scrutinizing gathered requirements for completeness, accuracy, and alignment with stakeholder intentions. * ***Requirements Management:*** A continuous process of collecting and managing new or changing requirements throughout the project's lifecycle. 6. **Design Phase:** The system architecture is planned, and detailed specifications (logical and physical blueprints) are created based on the approved requirements. This phase transforms requirements into a blueprint for development. * ***Algorithms:*** A precise, step-by-step procedure designed to solve a specific problem. For more on logic, see . | Algorithm to find the Percentage Marks | Algorithm to find the Student's Result | | :--- | :--- | | 1. Start | 1. Start | | 2. Read Total Marks, TM | 2. Read Percentage Marks, PM | | 3. Read Obtained Marks, OM | 3. If PM >= 40 Then Print "Pass" Else Print "Fail" | | 4. PM = (OM / TM) \* 100 | 4. End | | 5. Print "Percentage Marks", PM | | | 6. End | | * ***Flowcharts:*** A diagrammatic representation that illustrates an algorithm or process using standardized symbols. 7. **Development/Coding Phase:** Developers write the actual code based on the design specifications. The database structures are built, data flow processes are coded, and the user interface is created. For coding basics, see . 8. **Testing/Verification Phase:** The system is thoroughly tested to find and fix errors, commonly known as *bugs*. The goal is to ensure the system meets the specified requirements and functions correctly. * ***Black Box Testing:*** Testing the functionality of the software without knowledge of its internal code structure. The tester focuses only on inputs and expected outputs. * ***White Box Testing:*** Testing the internal structures and logic of the software. The tester has access to the source code and evaluates code paths, statements, and conditions. 9. **Deployment/Implementation Phase:** The finalized and tested software is delivered to the client or released to the market. This involves installation, configuration, user training, and transitioning from the old system to the new one. * **Deployment Methods:** * *Direct:* The old system is completely replaced by the new system at once. * *Parallel:* Both old and new systems run simultaneously for a period. * *Phased:* The new system is introduced in stages or modules. * *Pilot:* The new system is rolled out to a small group of users first for testing and feedback. 10. **Documentation Phase:** Creating detailed records of the system's design, architecture, and user instructions. This is crucial for future maintenance, error diagnosis, and user training. 11. **Maintenance/Support Phase:** An ongoing process of monitoring, modifying, and enhancing the system after deployment. This includes fixing newly discovered bugs, updating the system to meet new requirements, and ensuring it continues to perform as expected. ### **1.4.2 Software Development Models** These models provide a structured framework for managing the software development process. #### **Waterfall Model** A linear, sequential approach where progress flows steadily downwards through the phases of development, much like a waterfall. Each phase must be fully completed before the next begins. * **Phases:** Requirements -> Design -> Development -> Testing -> Deployment -> Maintenance. * **Best For:** Projects with stable, well-defined requirements that are unlikely to change. * **Advantages:** Simple to understand, easy to manage, well-documented. * **Disadvantages:** Inflexible to change, long delivery time, high risk if requirements are misunderstood. #### **Agile Model** An iterative and incremental approach that emphasizes flexibility, collaboration, and customer feedback. The project is broken down into small, rapid cycles called *sprints*. * **Phases:** The phases (Requirements, Planning, Design, Implementation, Testing, etc.) are repeated in each iterative cycle. * **Best For:** Projects where requirements are expected to evolve and change. * **Advantages:** Flexible and adaptive, high customer satisfaction due to continuous involvement, early delivery of functional software. * **Disadvantages:** Heavy reliance on customer availability, potential for scope creep, can be challenging for large teams. | Feature | Waterfall Model | Agile Model | | :--- | :--- | :--- | | **Approach** | Linear, Sequential | Iterative, Incremental | | **Flexibility** | Rigid, difficult to change | Highly flexible and adaptive | | **Customer Involvement**| Limited to the beginning | Continuous throughout the project | | **Delivery** | Single delivery at the end | Frequent, small deliveries | | **Best Suited For** | Projects with stable, clear requirements | Projects with evolving requirements |