Functional perspective this perspective documents

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Functional perspective: This perspective documents which information of the system context is being manipulated by the system to be devel- oped and which data is being transmitted to the system context by the system. Behavioral perspective: The embedding of the system in the system con- text is documented on the basis of states in this perspective. This is done, for instance, by documenting the reaction of the system to events within the system context, documenting the conditions that trigger a state change, or documenting the effects that the system has on its envi- ronment. Examples of the three perspectives Figure 6-5 illustrates the three perspectives on functional requirements and gives an example of a suitable modeling language for each perspective that can be used to document the requirements. This way, requirements aspects that pertain to the static structure can be modeled using UML class diagrams, for instance. Requirements in the functional perspective can be modeled using UML activity diagrams and requirements in the behavioral perspective can be modeled using statecharts (see sections 6.6 and 6.7 ). Perspectives are not disjoint. Certain aspects of the models of a particular perspective can also be found in other perspectives. The three perspectives are therefore not dis- joint. For example, the data, whose static structure is defined in a UML class diagram can potentially also be found in the functional perspective because it depicts the inputs and outputs of actions in a UML activity dia- gram. As the three perspectives are not disjoint, the models can be recip- rocally checked for completeness and consistency with regard to the infor- mation that is modeled at the intersections.
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6.5 Requirements Modeling in the Data Perspective 71 Figure 6-5 Three perspectives on requirements 6.5 Requirements Modeling in the Data Perspective Several different modeling languages are well suited to modeling structural aspects of requirements in the data perspective. Commonly, entity-rela- tionship models, extensions of the traditional entity-relationship model according to Chen [Chen 1976.], and, increasingly, class diagrams of the UML (e.g., [Rumbaugh et al. 2005] ) are used as requirements models of the data perspective. 6.5.1 Entity-Relationship Diagrams The traditional entity- relationship model Traditionally, entity-relationship diagrams are used for modeling the data perspective because they display the structure of an object of an universe of discourse by means of entity types and relation types [Chen 1976] . Extensions of the entity- relationship model A number of extensions for the entity-relationship model have been suggested. These extensions mainly concern the generalization/specializa- tion relations, inheritance mechanisms, and roles of entities and extend the model by a (min, max)-notation for cardinalities of relations.
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