Software Development Life Cycle

Software Development Life Cycle

1. 1-SOFTWARE DEVELOPMENT LIFE CYCLE MODEL

   • Requirements
   • Design
     • In the design phase, the results of the requirements-gathering phase are translated into a software design plan. Focus shifts from the system's results to the way in which those results will be achieved and how the ideas of the requirements-gathering phase are accomplished. Designers consider many different criteria, from the hardware and operating system platform that hosting the software to the way subsystems will communicate with each other. In essence, during the design phase, the designers attempt to turn the dreams of the managers and users into reality. Emphasis during this phase is on making a practical, working design for what has been outlined in the requirements-gathering phase.
   • Implementation
   • Testing
   • The term software development life cycle model is a way of describing the planning, designing, coding, and testing of a software system, as well as the method in which these steps are implemented. A variety of life cycle models exist, but they all include the same constituent parts. All life cycle models take a project through several primary phases: a requirements-gathering phase, a design phase, a construction or implementation phase, and a testing phase. Figure 4-1 provides a simplified illustration of the general software development life cycle model.

2. 2-WATERFALL LIFE CYCLE MODEL

   • Requirements
     • Design
       • Implementation and Unit Testing
         • Integration and System Testing
           • Operation
   • The Waterfall life cycle model, also known as the classic or linear-sequential life cycle model, is one of the simplest to understand and use. The Waterfall model is characterized by a series of steps that must be completed in a linear, sequential order. Each phase is completed and verified before development progresses to the next phase. Figure 4-2 illustrates the Waterfall life cycle model.

3. Requirements

   • High Level Design
     • Low Level Design
       • Implementation
         • Unit Testing
           • Integration Testing
             • System Testing
         • 3-V-SHAPED LIFE CYCLE MODEL
           • Like the Waterfall model, the V-Shaped life cycle model provides a sequential path of discrete phases that must each be completed before development proceeds to the next phase. The phase test plans are developed during each level of development, and once coding is completed, the tests are conducted. Figure 4-3 is a simplified illustration of the V-Shaped life cycle model.
   • System Test Planning
     • Integration Test Planning
       • Unit Test Planning

4. 4-INCREMENTAL LIFE CYCLE MODEL

   • Requirements
     • Design
       • Implementation and Unit Testing
         • Integration and System Testing
           • Operation
   • The Incremental life cycle model builds an iterative approach into the Waterfall model. Development projects are divided into several smaller, more manageable iterations. Each iteration passes through a mini-Waterfall process. Requirement, design, implementation and testing phases are completed for each iteration. Figure 4-4 illustrates the Incremental life cycle model.

5. 5-Advantages of the Incremental model

   • Planning
     • Risk Analysis
       • Engineering
         • Evaluation
           • Customer Evaluation
             • Project Cost
               • Requirements Gathering
                 • Risk Analysis
                   • Prototyping
                     • Coding
                       • Testing
   • The Spiral model is represented by a spiral passing through four quadrants, which represent the four phases of development. Requirements gathering is performed in the planning phase. During the risk analysis phase, a formal process is undertaken to identify alternative courses of action and their relative risks. A prototype is also developed during this phase. Software is coded and tested during the engineering phase. During the evaluation phase, the customer has an opportunity to evaluate the output before the project proceeds to the next spiral. Notice that the angular component represents the progress in the current spiral, and the radius represents the project cost. Figure 4-5 illustrates the Spiral life cycle model.