A data flow diagram is a picture of the movement of

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A data flow diagram is a picture of the movement of data between external entities and theprocesses and data stores within a system.Systems analysts use data flow diagrams to help them model the processes internal to aninformation system as well as how data from the system’s environment enter the system, areused by the system, and are returned to the environment.DFDs help analysts understandhow the organization handles information and what its information needs are or might be.Analysts also use DFDs to study alternative information handling procedures during theprocess of designing new information services.
2.Explain the rules for drawing good DFDs.
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Chapter 11 / Exercise 6
Introduction to Learning and Behavior
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Data cannot move directly to an outside sink from a data store.Data must be moved byprocesses.A data store has a noun phrase label.Source/Sink:Data cannot move directly from a source to a sink.Data must be moved by a process.Ifthe data are of any concern to our system.Otherwise, the data flow is not shown on theDFD.A source/sink has a noun phrase labelData Flow:A data flow has only one direction of flow between symbols.It may flow in bothdirections between a process and a data store to show a read before an update.The latteris usually indicated; however, by two separate arrows because these happen at differenttimes.A fork in a data flow means that exactly the same data goes from a common locationtotwo or more different processes, data stores, or sources/sinks (this usually indicatesdifferent copies of the same data going to different locations).A join in a data flow means that exactly the same data come from any of two or moredifferent processes, data stores, or sources/sinks to a common location.A data flow cannot go directly back to the same process it leaves.There must be at leastone other process that handles the data flow, produces some other data flow, and returnsthe original data flow to the beginning process.A data flow to a data store means update (delete or change).A data flow from a data store means retrieve or use.A data flow has a noun phrase label.More than one data flow noun phrase can appear ona single arrow as long as all of the flows on the same arrow move together as onepackage.

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DFDs
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Introduction to Learning and Behavior
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Chapter 11 / Exercise 6
Introduction to Learning and Behavior
Honey/Powell
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