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Data Flow Diagrams Overview
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Data Flow Diagrams Overview
Data Flow Diagrams Overview
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Question
What is the purpose of process modeling in system analysis?
Answer
Process modeling graphically represents processes that capture, manipulate, store, and distribute data between a system and its environment and among system components, utilizing information gathered during requirements determination to model processes and data structures.
Question
How is a Data Flow Diagram (DFD) defined?
Answer
A Data Flow Diagram is a graphical representation showing the movement of data between external entities and the processes and data stores within a system, illustrating data in motion from one part of a system to another.
Question
What are some examples of data that data flows in a DFD could represent?
Answer
Data flows could represent information on a customer order form, a payroll check, results of a database query, contents of a printed report, or data on a data entry computer display form.
Question
What do the four key symbols in a Data Flow Diagram (DFD) represent?
Answer
The key DFD symbols represent: Process (work/actions performed on data inside the system), Data Store (data at rest inside the system), Source/Sink (external entities outside the system that are origin or destination of data), and Data Flow (arrows depicting data movement).
Question
What are the diagramming rules related to processes in a DFD?
Answer
In a DFD, each process must have both inputs and outputs; processes cannot have only inputs or only outputs, and process labels should be verb phrases to describe the actions performed.
Question
What are the diagramming rules related to data stores in a DFD?
Answer
Data stores must have one input and one output, all flows to or from a data store must move through a process, and data store labels should be noun phrases describing what is stored.
Question
What are the important constraints for source/sink entities in a DFD?
Answer
No data moves directly between external entities without going through a process; interactions between external entities without intervening processes are outside the system and not represented in the DFD. Source and sink labels should be noun phrases.
Question
How is bidirectional data flow between a process and a data store represented in a DFD?
Answer
Bidirectional flow is represented by two separate arrows: one for data moving from the process to the data store and another for data moving from the data store to the process.
Question
What must be true about forked and joined data flows in a DFD?
Answer
Forked data flow must refer to the exact same data item sent from one source to multiple destinations, while joined data flow must refer to the exact same data item coming from multiple sources to a common destination.
Question
Why can data flow not go directly from a process to itself in a DFD?
Answer
Data flow cannot go directly from a process to itself because the data must go through intervening processes; this prevents illogical or meaningless data loops within a single process.