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10/21/99 Prof. Ann Hickey 1
Chapter 8 (continued)
Process Modeling
10/21/99 Prof. Ann Hickey 2
Class Outline - DFDs
DFD Decomposition Context Diagram Level-0 DFD Level-1 to Level-n DFDs
Types of DFDs Current or Proposed System Logical or Physical Description
DFD AnalysisDFD Discussion (Problem 13a & 13b)
Data Flow Diagram Set
Context Diagram Level-0 DFD
Level-1 DFDs
Level-n DFDs
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....
....
....Primitive DFDs
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Primitive DFDs
Lowest level of decomposition for a DFD
Stop decomposing when: Process is a single decision, calculation, DB
operation, or menu choice Data store represents single entity Data flows do not need further splitting Each form, transaction, display, & report is
represented as a single data flow
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Types of DFDs
PhysicalDescription
LogicalDescription
CurrentSystem
NewSystem
1
2 3
4
Figure 8-13a: Context DiagramHoosier Burger’s Current Physical Inventory Control
©1999 Addison Wesley Longman
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See Text, Figure 8-13a, p. 294
Figure 8-13b: Level-0 Data Flow DiagramHoosier Burger’s Current Physical Inventory Control System
©1999 Addison Wesley Longman
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See Text, Figure 8-13b, p. 294
Figure 8-15: Level-0 Data Flow Diagram Hoosier Burger’s Current Logical Inventory Control System
©1999 Addison Wesley Longman
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See Text, Figure 8-15, p. 296
Figure 8-16: Level-0 Data Flow Diagram Hoosier Burger’s New Logical Inventory Control System
©1999 Addison Wesley Longman
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See Text, Figure 8-16, p. 297
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Additional DFD GuidelinesCompleteness
All necessary DFD components included & fully described
Consistency Compatible system descriptions at all levels
Timing Not shown on DFDs; use other diagrams
Iterative Development Parallel rqmts determination & structuring Quality DFDs require multiple revisions
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DFD Analysis
Gap Analysis - Discover discrepancies between sets of DFDs/single DFD
Problem/Inefficiency Analysis Redundant data flows Unused data Identical data updates Excessive processing steps
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ConclusionDFDs are a simple, graphical method for
modeling processes and data flowsMany possible DFD representations of a
system; should be mechanically correctGood DFDs require multiple iterationsFour types of DFDs: current physical,
current logical, new logical, new physical -- focus on New Logical DFDs quickly
