Note for Principles and Practices in Software Engineering - PPSE by MAVRICKS PROGRAMMERS

Topics ( 6 )

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The selection of model has very high impact on the testing that is carried out. It will define the what, where and when of our planned testing, influence regression testing and largely determines which test techniques to use. There are various Software development models or methodologies. They are as follows: 1. 2. 3. 4. 5. 6. 7. 8. Waterfall model V model Incremental model RAD model Agile model Iterative model Spiral model Prototype model Choosing right model for developing of the software product or application is very important. Based on the model the development and testing processes are carried out. Different companies based on the software application or product, they select the type of development model whichever suits to their application. But these days in market the ‘Agile Methodology’ is the most used model. ‘Waterfall Model’ is the very old model. In ‘Waterfall Model’ testing starts only after the development is completed. Because of which there are many defects and failures which are reported at the end. So, the cost of fixing these issues are high. Hence, these days’ people are preferring ‘Agile Model’. In ‘Agile Model’ after every sprint there is a demo-able feature to the customer. Hence customer can see the features whether they are satisfying their need or not. ‘V-model ‘is also used by many of the companies in their product. ‘V-model’ is nothing but ‘Verification’ and ‘Validation’ model. In ‘V-model’ the developer’s life cycle and tester’s life cycle are mapped to each other. In this model testing is done side by side of the development. Likewise ‘Incremental model’, ‘RAD model’, ‘Iterative model’ and ‘Spiral model’ are also used based on the requirement of the customer and need of the product. What is Waterfall model- advantages, disadvantages and when to use it?

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The Waterfall Model was first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very simple to understand and use. In a waterfall model, each phase must be completed fully before the next phase can begin. This type of software development model is basically used f for the project which is small and there are no uncertain requirements. At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project. In this model software testing starts only after the development is complete. In waterfall model phases do not overlap. Diagram of Waterfall-model: Advantages of waterfall model: • This model is simple and easy to understand and use.

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• • • It is easy to manage due to the rigidity of the model – each phase has specific deliverables and a review process. In this model phases are processed and completed one at a time. Phases do not overlap. Waterfall model works well for smaller projects where requirements are very well understood. Disadvantages of waterfall model: • • • • • • Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage. No working software is produced until late during the life cycle. High amounts of risk and uncertainty. Not a good model for complex and object-oriented projects. Poor model for long and ongoing projects. Not suitable for the projects where requirements are at a moderate to high risk of changing. When to use the waterfall model: • • • • • • This model is used only when the requirements are very well known, clear and fixed. Product definition is stable. Technology is understood. There are no ambiguous requirements Ample resources with required expertise are available freely The project is short. Very less customer interaction is involved during the development of the product. Once the product is ready then only it can be demoed to the end users. Once the product is developed and if any failure occurs then the cost of fixing such issues are very high, because we need to update everywhere from document till the logic. What is agile model – advantages, disadvantages and when to use it? Agile development model is also a type of Incremental model. Software is developed in incremental, rapid cycles. This results in small incremental releases with each release building on previous functionality. Each release is thoroughly tested to ensure software quality is maintained. It is used for time critical applications. Extreme Programming (XP) is currently one of the most well-known agile development life cycle model. diagram of Agile model:

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Advantages of Agile model: • • • • • • • • Customer satisfaction by rapid, continuous delivery of useful software. People and interactions are emphasized rather than process and tools. Customers, developers and testers constantly interact with each other. Working software is delivered frequently (weeks rather than months). Face-to-face conversation is the best form of communication. Close, daily cooperation between business people and developers. Continuous attention to technical excellence and good design. Regular adaptation to changing circumstances. Even late changes in requirements are welcomed Disadvantages of Agile model: • • • • In case of some software deliverables, especially the large ones, it is difficult to assess the effort required at the beginning of the software development life cycle. There is lack of emphasis on necessary designing and documentation. The project can easily get taken off track if the customer representative is not clear what final outcome that they want. Only senior programmers are capable of taking the kind of decisions required during the development process. Hence it has no place for newbie programmers, unless combined with experienced resources. When to use agile model: • • When new changes are needed to be implemented. The freedom agile gives to change is very important. New changes can be implemented at very little cost because of the frequency of new increments that are produced. To implement a new feature the developers need to lose only the work of a few days, or even only hours, to roll back and implement it.