In addition further perspectives that emerge from the

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In addition, further perspectives that emerge from the individual context of the development project can be created as need be. Define validation directives for each perspective. During perspective-based validation, each auditor is assigned a per- spective (at the proper point in time) from which she reads and validates the requirement. For each perspective defined, detailed instructions for performing the validation should be laid down because the auditor might
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7.5 Requirements Validation Techniques 101 not be familiar with all relevant details of her assigned perspective. It is advisable to associate questions with each validation instruction that must be answered by the content of the requirements or by the auditor after she has read the requirement, respectively. In addition, validation instructions can be amended with a checklist that summarizes the most important con- tent aspects that ought to be addressed by a requirement with regard to the appropriate perspective. Follow-up During the course of the follow-up to a perspective-based reading ses- sion, the results of the chosen perspective are analyzed and consolidated. On the one hand, the results of the perspective-based reading contain answers to the predefined questions, and on the other hand, open issues that the auditors noticed while reading may be present. The consolidation can be done as a group effort, similarly to a review. Support of other techniques Perspective-based reading can be both an independent technique for requirements validation and a support technique for other validation tech- niques, such as inspections or reviews of requirements documents by means of perspective-based reading. 7.5.5 Validation through Prototypes Requirements validation by means of prototypes allows auditors to expe- rience the requirements and to try them out. Experiencing requirements directly through prototypes [Jones 1998] is the most effective method to identify errors in requirements. Stakeholders can try out the prototype and compare their own idea of how the system ought to be implemented with the prototype at hand and thereby find discrepancies between their ideas and the current implementation. Evolutionary vs. throw-away prototypes Depending on the further use of the prototype, one can distinguish between throw-away prototypes and evolutionary prototypes [Sommer- ville 2007] . Throw-away prototypes are not maintained once they have been used. Evolutionary prototypes are developed with the goal to be developed further and improved in later steps. In contrast to throw-away prototypes, implementation plays a much more significant role here. Therefore, the effort to create evolutionary prototypes is much higher. Selection of relevant requirements Before a prototype can be implemented, the requirements that shall be validated through the prototype must be selected. The set of requirements to be validated is limited by development resources (e.g., time, money, etc.) that can be allocated for validation. For example, a selection criterion can be the criticality of a requirement.
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