Functional perspective functional perspective the

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Functional perspective Functional perspective: The functional perspective documents which information (data) is received from the system context and manipulated
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4.2 Types of Documentation 35 by the system or one of its functions. This perspective also documents which data flows back into the system context. The order in which functions processing the input data are executed is also documented. Behavioral perspective Behavioral perspective: In the behavioral perspective, information about the system and how it is embedded into the system context is documented in a state-oriented manner. This is done by documenting the reactions of the system upon events in the system context, the con- ditions that warrant a state transition, and the effects that the system shall have on its environment (e.g., effects of the system analyzed that represent events in the system context of a different system). 4.2.2 Requirements Documentation using Natural Language Advantages of using natural language Natural language, particularly prose, is the most commonly applied docu- mentation form for requirements in practice. In contrast to other docu- mentation forms, prose has a striking advantage: No stakeholder has to learn a new notation. In addition, language can be used for miscellaneous purposes—the requirements engineer can use natural language to express any kind of requirement. Disadvantages of using natural language Natural-language-based documentation is well suited to document requirements in any of the three perspectives. However, natural language can allow requirements to be ambiguous, and requirements of different types and perspectives are in danger of being unintentionally mixed up during documentation. In that case, it is difficult to isolate information pertaining to a certain perspective amidst all of the requirements in natu- ral language. 4.2.3 Requirements Documentation using Conceptual Models In contrast to natural language, the different types of conceptual models cannot be used universally. When documenting requirements by means of models, special modeling languages must be used that pertain to the appropriate perspective. Assuming the modeling language selected for a documentation task is applied correctly, its use constructively guarantees that the models created depict information pertaining to the respective perspective only. The models depict the documented requirements much more compactly and they therefore are easier for a trained reader to under- stand than is natural language. In addition, conceptual models offer a decreased degree of ambiguity (i.e., fewer ways to be interpreted) than
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36 4 Documenting Requirements natural language due to their higher degree of formality. However, using conceptual modeling languages for requirements documentation requires specific knowledge of modeling. The following list includes short descrip- tions of the most important diagrams discussed in chapter 6.
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