Thespiral model combines the idea of iterative development with the systematic,controlled aspects of the waterfall model. The spiral model has four phases. Asoftware project repeatedly passes through these phases in iterations calledSpirals.
This means that the product is released incrementally.TheIdentification phase starts with gathering the business requirements in thebase spiral. In the subsequent spirals as the product matures, identificationof system requirements, subsystem requirements and unit requirements are alldone in this phase. The proof of concept includes identifying, estimating andmonitoring the technical feasibility and management risks, such as scheduleslippage and cost overrun.
After testing the build, at the end of firstiteration, the customer evaluates the software and provides feedback. Thisphase also includes understanding the system requirements by continuouscommunication between the customer and the system analyst. TheDesign phase starts with the conceptual design in the baseline spiral andinvolves architectural design, logical design of modules, physical productdesign and the final design in the subsequent spirals. The architecture of theapplication is designed in this stage, which means the structure of theapplication for example UI features, such as colours, text, tabs, buttons andlinks. After that each module in the application is designed and finally thewhole system is designed in the last build.
The customer gives feedback on thisdesign in the evaluation stage at the end of the iteration. The Buildphase refers to production of the actual software product at every spiral. Inthe base spiral, the product is implemented by software developers, which codethe application so that it functions properly. The developers have to followthe design supplied by the designers. Another build is created later on in thedevelopment, so that new implementations could be provided, which could be moreefficient. The first build is used as a back up if the second build fails. Thebuild is tested in the evaluation stage.
Theevaluation phase consists of managing risks in the application used to tocontain and mitigate threats in the product and also testing how theapplication works, which is done to make the code more efficient and reduceerrors found in the build of the product. The customer gives feedback to thedesign and the build of the system, to see how the product development is beingcompleted. The spiral model is appliedwhen: When the budget is low and risks need to be evaluated Project is medium to high risk. Customer is not sure of their requirements. Requirements are complex and need evaluation to get clarity. Significant changes are expected in the product during the development cycle.Advantages of spiral model: Requirements can be changed.
Promotes the use of prototypes. Requirements can be defined more accurately. Users can see the system in early stages of development. Development can be divided into modules and the difficult modules can be developed earlier.Disadvantages of the model: End of the project may not be known early . Management is more complex. Spiral may go on indefinitely. Not suitable for small or low risk projects WaterfallOfthe many project management models in use today, the waterfall model is one ofthe most easily understandable and manageable models.
The waterfall model is a projectmanagement methodology based on a sequential design process. Much like awaterfall filling lower level pools, phases in the waterfall model flow fromone to another. Also like the pools filling completely before water spills intothe next pool, the waterfall model finishes one phase before another phase canbegin.Developedas a software development life cycle model, waterfall methodology lends itselfto projects that are small in size and whose requirements can be definitivelydetermined up front. A simple waterfall model has 6 phases: requirementsanalysis, design, implementation, testing, deployment, and maintenance.The first phase of thewaterfall model is requirement analysis and in this phase, in which thestakeholders analyse the requirements that will be needed to create the