Data Flow Diagramming Rules Basic rules that apply

Data Flow Diagramming Rules Basic rules that apply to all DFDs n n Inputs to a process are always different than outputs Objects always have a unique name w In order to keep the diagram uncluttered, you can repeat data stores and sources/sinks on a diagram 8. 1

Data Flow Diagramming Rules Process n n n 8. 2 No process can have only outputs (a miracle) No process can have only inputs (black hole) A process has a verb phrase label Data Store n n Data cannot be moved directly from one store to another Data cannot move directly from an outside source to a data store Data cannot move directly from a data store to a data sink Data store has a noun phrase label

Data Flow Diagramming Rules Source/Sink n n 8. 3 Data cannot move directly from a source to a sink A source/sink has a noun phrase label Data Flow n n A data flow has only one direction of flow between symbols A fork means that exactly the same data goes from a common location to two or more processes, data stores or sources/sinks

Data Flow Diagramming Rules Data Flow (Continued) L. A join means that exactly the same data comes from any two or more different processes, data stores or sources/sinks to a common location M. A data flow cannot go directly back to the same process it leaves N. A data flow to a data store means update O. A data flow from a data store means retrieve or use P. A data flow has a noun phrase label 8. 4

8. 5

Incorrect and Correct ways to draw data flow diagram 8. 6

Decomposition of DFDs Functional decomposition n Act of going from one single system to many component processes Repetitive procedure Lowest level is called a primitive DFD Level-N Diagrams n 8. 7 A DFD that is the result of n nested decompositions of a series of subprocesses from a process on a level-0 diagram

Figure 8 -4 Context diagram of Hoosier Burger’s food ordering system 8. 8

Figure 8 -5 Level-0 DFD of Hoosier Burger’s food ordering system 8. 9

Level-1 diagram showing the decomposition of process 1. 0 from the level-0 diagram for Hoosier Burger’s food ordering system 8. 10

Level-1 diagram showing the decomposition of process 4. 0 from the level-0 diagram for Hoosier Burger’s food ordering system 8. 11

Level-2 diagram showing Process 4. 3 from the level-1 diagram for process 4. 0 for Hoosier Burger’s food ordering system 8. 12