Flowing data A data flow describes data that is transported between processes

Flowing data a data flow describes data that is

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Flowing data A data flow describes data that is transported between processes, data stores, and sources/sinks [Yourdon 1989] . In requirements models, a data flow can model both the transport of material and immaterial objects, e.g., information flow or material flow. Typically, only the most important data flows are modeled in data flow diagrams. Data flows that are not relevant for the requirements of the system can be neglected. Example of a Data Flow Diagram System interfaces Figure 6-11 shows a simplified data flow diagram of a navigation system in the notation suggested by DeMarco. The interfaces of the system to the Data Flow Process Source/Sink Data Store [Name] [Name] [Name] [Name] 7. In the structured analysis, the flow of data, information, documents, or material is considered a data flow.
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78 6 Model-Based Requirements Documentation context are defined by the data flows to the sources “GPS satellite system” and “traffic information server” as well as to the sink “driver”. Process “calculate route” The functionality of the navigation system is separated into three dis- tinct processes. Process one, named “calculate route”, receives up-to-date traffic information via its interface to the source “traffic information server” as well as data about the current location via its interface to the source “GPS satellite system”. In addition, the process “calculate route” is provided with the desired destination by the driver of the vehicle. The cal- culated route is stored in the data store “route data”. Process “determine next waypoint” Process two—“determine next waypoint”—accesses the data store and retrieves data concerning the current route. The process determines the next waypoint and outputs this information. Process “recalculate route” Process three—“recalculate route”—plots a new course to the destina- tion. In order to do so, it gathers traffic information from the source “traf- fic information server” and, potentially, information about the current location. The newly calculated course is stored in the data store “route data”. Figure 6-11 Data flow diagram in the notation suggested by DeMarco 6.6.2 Models of the Functional Perspective and Control Flow In data flow diagrams, it cannot be seen which conditions trigger which processes. Data flow diagrams merely depict data dependencies of the processes in a system and document necessary input and generated output data. Approaches used in structured system analysis, however, often offer Route data Driver Recalculate route Deviant location Determine next waypoint Calculate route Location data Traffic information server GPS satellite system
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