Transcript Appendix B - Official Site of Parno

MANAGEMENT INFORMATION SYSTEMS 8/E
Raymond McLeod, Jr. and George Schell
Appendix B
Process Modeling
Copyright 2001 Prentice-Hall, Inc.
B-1
Data Flow Diagrams (DFDs)

Graphic representation of a system that uses
a small number of symbol shapes to
illustrate how data flows through
interconnected processes
– Most natural way to document processes
– Emphasis on processes rather than data
B-2
DFD Symbols

DFDs consist of four symbols
1) Environmental elements called terminators
» Person
» Organization
» Another system
2) Processes which transform inputs to outputs
» Labeled with verb and object
» Also labeled with system or computer program
name
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DFD Symbols [cont.]

DFD symbols [cont.]
– Data flows which consist of logically related
data elements that travel from one point or
process to another. In other words, data in
motion.
» Structures
» Diverge
» Converge
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DFD Symbols [cont.]

DFD symbols [cont.]
– Data stores which are data repositories. In
other words, data at rest.
B-5
Mail
Customer
1.
Open
mail
Entered
sales order
data
3.
Sort
sales
order s
A Data Flow Diagram (Figure 0
Diagram) of a Sales Commission
System
Sales
orders
2.
Enter sales
order data
Entered
sales orders
Sales order
form file
Sorted
sales
records
4.
Compute
sales
commissions
Sales commission
report
Sales
manager
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When Drawing a Context
Diagram
1. Use only a single process symbol
2. Label the process symbol to represent the
entire system
3. Do not number the single process symbol
4. Include all terminators for the system
5. Show all the data flows between the
terminators and the system
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Mail
Customer
A Context Diagram of a
Sales Commission System
Sales
Commission
System
Sales
commission
report
Sales
Manager
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Figure n Diagrams
Documents a single process of a DFD in a
greater amount of detail
 n represents the number of the process on
the next higher level that is being
documented
 The term “leveled DFDs” describe the
hierarchy of diagrams ranging from context
to the lowest-level figure n diagram

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Figure 4 Diagram of a Sales Commission System
3
Sorted
sales
records
4.1
Compute
commission
amounts
Sales
commission
report
4.2
Accumulate
totals
Sales
manager
Commission
amounts
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How Many Levels to Use?
Restrict a single DFD to no more than six to
eight processes
 Use another tool to document the lowest
level of detail but use no more than a single
page.

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Data Flow Diagramming
Guidelines
1. Label each data flow with a unique name.
2. Keep data flow names constant between levels.
3. Show proper disposition of records deleted from a data
store.
4. When documenting a computer program, do not include
reads/writes.
5. Avoid read-only processes.
6. Write-only processes are permissible when time serves as
the trigger.
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Structured English
Narrative form of computer code
documentation
 Based on Pseudocode
 Abbreviated, formalized pseudocode in a
particular format that looks like computer
code

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Structured English Guidelines
1) Use a verb when describing each
processing strip.
 2) Supplement verb with one or more
objects when necessary.
 3) Use only three constructs of
programming.

– Sequence
– Selection
– Repetition
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Structured English
Guidelines [cont.]
4) Use only data names defined in the data
dictionary.
 5) Use uppercase for all data names and
computer syntax.
 6) Indent to show a hierarchical structure.

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Structured English
Guidelines [cont.]
7) When documentation is subdivided into
modules, use the first line of each module
for an identifying label and leave at least
one blank line in-between.
 8) Restrict each module to a single entry
and exit point.

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Structure English Example
START
Initialize storage
TOTAL.SALES, TOT.COM = 0
Process sales data
DO WHILE (more records)
PERFORM READ DATA
PERFORM PROCESS DATA
PERFORM PRINT DATA
END DO
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Summary
Process modeling is an important part of
system design
 Various techniques exist for process
modeling

– DFDs
– Structured English

Manager can use Structured English and
DFDs to communicate system requirements
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