The interface type in turn may also impose specific

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interface). The interface type in turn may also impose specific constraints or additional sources of requirements on the system to be developed. Gray zone between system and system context Frequently, the system boundary is not precisely defined until the end of the requirements engineering process. Before that, some or several interfaces as well as desired functions and qualities of the system to be developed are only partially known or not known at all. We refer to this initially vague separation of the system and its context as the gray zone between the system and the context (see figure 2-3 ). At the beginning of the requirements engineering process, it may, for example, not be clear whether the system should implement a certain function (e.g., “pay by credit card”) or whether there is another system in the system context providing such a function that should be used (e.g., “payment process- ing”).
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2.2 Defining System and Context Boundaries 15 Adjusting the gray zone The system boundary may not only shift within the gray zone ( 1 in figure 2-3) but also the gray zone itself may shift during the requirements engineering process ( 2 in figure 2-3 ). This kind of shifting is caused by the fact that aspects, pertaining at first to the system context, now will be modified during system development. Such a situation occurs during requirements engineering, for example, if it is not clear in the system con- text whether certain activities of a business process should be imple- mented or supported by the system to be developed or not. In this situa- tion, it is not clear which aspects belong to the system and can thus be changed or modified and which aspects belong to the system context. This causes a corresponding shift of the gray zone between system and system context (see figure 2-3 ). Figure 2-3 Gray zone of the system boundary The gray zone shifts, for instance, when interfaces are attributed to the system boundary and the gray zone is extended to comprise aspects of the environment that concern these interfaces. 2.2.2 Defining the Context Boundary The context boundary distinguishes between context aspects, i.e., those aspects of the environment that need to be taken into account during requirements engineering (e.g., as requirements sources) and those aspects that are irrelevant for the system. The context boundary can be defined as follows:
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16 2 System and Context Boundaries Concretion and shift of the context boundary At the beginning of the requirements engineering process, frequently only part of the environment as well as single specific relationships between the environment and the system to be developed are known. In the course of requirements engineering, it is necessary to concretize the boundary between system context and irrelevant environment by analyzing relevant aspects within the environment with regard to their relationships to the system. Besides the system boundary, the context boundary typically also shifts during requirements engineering. For instance, it may be possible
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