Behavioral perspective requirements eg statecharts eg

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Behavioral perspective Requirements e.g. statecharts e.g. UML class diagrams e.g. UML activity diagrams
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72 6 Model-Based Requirements Documentation Modeling Elements of Entity-Relationship Diagrams According to [Chen 1976] , the modeling language used to construct entity- relationship diagrams includes the modeling elements depicted in figure 6-6. Figure 6-6 Important modeling elements of entity-relationship diagrams according to Chen Classification: abstraction from concrete objects Entity types define a set of entities within the universe of discourse (that is, objects with the same properties, such as people or items). An entity type (often mistakenly referred to as an entity) abstracts from the concrete char- acteristics of these entities and therefore classifies a set in the sense of the classification of uniform entities. For instance, the entity type “pilot” clas- sifies all people within the universe of discourse that have the characteristic of holding a piloting license. Abstraction from concrete relationships A relation type abstracts from a concrete characteristic of a relation- ship and of entities that are in relation to one another. A relation type clas- sifies the set of uniform relations between entity types within the universe of discourse. For example the relation type “executes” can be defined between the two entity types “pilot” and “flight” to represent concrete “executes”-relations between concrete pilots and concrete flights. If a con- crete “is_passenger” relation is defined between a concrete passenger “John Locke” 4 and a concrete flight with the flight number “OA 815” 5 , then this relation depicts that “John Locke” is a passenger of the flight with the flight number “OA 815”. Properties of entity types and relation types An attribute can be defined for entity types as well as relation types. An attribute defines the properties of an entity type or a relation type. Pos- sible attributes for the entity type “passenger” could be “family name”, “given name”, “passport number”, and “reserved seat”, for instance. Sketch level vs. instance level An entity-relationship model documents the structure of a universe of discourse by means of entity types (i.e., classes of uniform entities) and 4. More precisely, there is an entity that is an instance of the entity type “passenger” that pos- sesses a unique identity and has the attribute value “John Locke” for the attribute “name”. 5. More precisely, there is an entity that is an instance of the entity type “flight” that pos- sesses a unique identity and has the attribute value “OA 815” for the attribute “flight number”.
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6.5 Requirements Modeling in the Data Perspective 73 relations (i.e., classes of uniform relationships). An entity-relationship model is defined on the modeling level and defines the set of all valid instances on the instance level.
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