Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Major Topics
Process Modeling and
Dataflow Diagrams (DFDs)
3 process modeling
3 data flow diagram symbols
3 data flow diagram levels
3 creating data flow diagrams
Merrill Warkentin
Mississippi State University
3 physical and logical DFDs
3 partitioning
3 (event driven modeling)
3 (use case and data flow diagrams)
2
© Merrill Warkentin, 2005
Process Modeling
Data Flow Diagrams (DFD)
3 Graphically representing the functions, or
processes, which capture, manipulate, store, and
distribute data between a system and its
environment and between components of a
system
3 Data Flow Diagram (DFD)
3 graphical representation of data processes
and flows throughout the organization
3 emphasizes logic of underlying system
3 based on general systems model
Input
3
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4
Output
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Advantages of DFD
Why Use DFD?
3 early understanding
of system technical implications
3 logical information flow of the system
3 determination of physical system
construction requirements
3 establishment of inter-relatedness
between business and systems
3 simplicity of notation
3 user involvement
with system development
3 establishment of manual and
automated systems requirements
5
Process
3 determine if data and
processes have been defined
properly
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Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
DFD - Four Symbols
DFD - Four Symbols
3 Process - work or actions performed on data so
that they are transformed, stored, or distributed
3 Date Store - data at rest, notebook, file folder,
database
3 Source/Sink - origin and/or destination of the
data (external entities)
3 Data flow - data in motion
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DFD Formatting Symbols
Entity
3 supply data to the system
3 external to boundaries of system
Entity
External Entities
2 sources and destinations of data
3 receive data/information from the system
3 data movement
Data Flow
2.1
Process
2 electronic exchange
2 paper documents
(sometimes shown as)
3 but not considered part of the system
3 transformation of data
2 from input to output
2.1
3 data depository for
D3
Data
Store
9
Entity
2 electronic files
2 paper files
(sometimes shown as)© Merrill Warkentin, 2005
Purchase
order
Enter
Process
orders
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2.1
Data Flows
Process
3 represent data being moved to or from
Processes
3 set of tasks performed on data
to convert inputs to outputs
2 an external entity
2 a process
2 a data store
3 labeled as a verb/noun
2 e.g., ENTER ORDERS
3 shown as a line with arrowheads
3 labeled with description of
the type of data, document, or report
3 data flow out always labeled differently than data flow in
2.1
2.1
Enter
Process
orders
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Order data
D3
Entity
Data
Open
order
file
Store
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Purchase
order
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Enter
Process
orders
Order
data
D3
Data
Open
order
file
Store
© Merrill Warkentin, 2005
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Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Processes - 4 Types
D3
3
3
3
3
3
3
3 create new data
3 change quality but not content of input
2 e.g., verify customer number
2 output = input = (verified) customer number
3 reorganize input
Data
Store
Data Stores
data at rest
corresponds to data files or tables
can be electronic or paper files
shown as a rectangle (electronic)
arrow into file means data written
arrow out means data read
2.1
1.0
2 sort
2 reformat
2 filter/select
Enter
Process
orders
Order
data
3 convey input without any change
Orders
D1
13
D3
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Data
Customer
data
Store
Data
Open
order
file
Store
D2
Data
PO
File
Store
© Merrill Warkentin, 2005
Balancing DFDs
Five guidelines for drawing DFDs
3 Inputs and outputs must be conserved between
levels of DFDs
3 Level n & n+1 must have the same inputs and
outputs
3 Completeness - all necessary components are
included and described
3 Consistency - information on one level is
included on other levels
3 Timing - a DFD does NOT indicate when the
system is flowing
3 Iterative development - it may take 3 or more
DFDs to get it right
3 Primitive DFDs (the lowest level DFD) - stop
decomposing when the lowest logical level is
reached
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Problems with DFDs
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Describe problems (handout)
3 Identify problems on the DFD
(see handout)
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page 3
Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
DFD Development/Levels
DFD Organization
3 context diagram
External
Entity
1
2 general highest level diagram
2 one process representing entire system
Input A
1.0
Name
Processof
System
External
Entity
2
External
Entity
3
Output C
Input B
3 diagram 0
2 exploded view of the entire system
2 up to nine processes
2 all external entities and data stores
1.0
External
Entity
1
Record A
D1
2 exploded view of each individual process
2 outlined in Diagram 0
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© Merrill Warkentin, 2005
Output C
External
Entity
3
Record E
Data Store
1
D2
Data Store
2
Record A
Record E
2.0
3.0
Record E
3.1
Data Flow D
External
Entity
2
Input B
Process
B
Data Flow D
Detailed
Process
C-A
3.2
Record 1
D5
Record
Store 1
Record 1
Detailed
Process
C-B
Process
C
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Creating the Context Diagram
© Merrill Warkentin, 2005
Context Diagram Example
3 highest level
3 contains only one process
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Drawing Diagram 0
Drawing Diagram 0
3 explode context diagram
3 start with data flow
from an external entity
3 work backwards
from an output data flow
3 examine data flow
3 analyze well defined process
3 take note of problem areas
2 more detail
2 close-ups of processes
2 data stores
2 lower-level
data flows
3 may include
up to 9 processes
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4.0
Process
D
Data Flow B
Data Flow C
3 child diagrams
3 original should be an
overview
2 basic inputs
2 general system
2 outputs
Process
A
Input A
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page 4
Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Creating Child Diagrams
Diagram 0 Example
3 more detailed levels
2 each process exploded further
3 parent process
2 exploded diagram 0 process
3 child diagram
2 resulting diagram
2 entities usually not shown at this level
2 may have error lines here only
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Child Diagram Examples
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Child Diagram Examples
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Rules & Guidelines for DFD
Child Diagram Examples
A data store must always be connected to a process.
2.1
This:
D3
Not this:
D3
Nor this:
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Data
Store
Data
Store
Entity
Data Flow
Data Flow
Data Flow
Process
D4
D4
Data
Store
Data
Store
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Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Rules & Guidelines for DFD
Naming Rules for Data Flows
External entity must always be connected to a process.
3 data flows must be named
2 use a NOUN
(what data are being used by a process?)
2.1
OK -
Entity
Data Flow
Process
3 output flow from a process
not OK -
Entity
2 must have a different name than the input flow
2 output cannot be the same as the input
Data Flow
Data
Store
D4
Data may flow out of one process and into another.
OK -
Process
3 data traveling together
2.2
2.1
Data Flow
31
Process
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Rules & Guidelines for Processes
3 if no input data flowing to them,
may not be properly represented
3 process performs one simple, well-defined task,
activity or function
3 must have at least one input and
one output data flow
3 should be uniquely numbered
on the flow diagram
3 description of the data attributes should be
contained in a similarly numbered table
structure / data attribute dictionary
2 if no input, process is creating output from “thin air”
(where is the data to be processed
into output coming from?
2 if no output, process is “black hole” or “data sink”
(why is data flowing to a process
that does not produce any output?)
2 you can create the dictionary by printing out the
ACCESS data structures for each table
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© Merrill Warkentin, 2005
Data Stores’ Rules & Guidelines
2 where did the data
in the data store come from?
33
2 should be shown
and named as one data flow
2 example: orders and payments flowing together
should be labeled as “orders and payments”
© Merrill Warkentin, 2005
34
3 data should be sent only to processes
that use them
© Merrill Warkentin, 2005
Rules & Guidelines for Processes
Common Errors
3 should be uniquely named and numbered
3 not including data flow
3 description of the process should be
in a similarly numbered and indexed
“process dictionary”
3 placing arrowhead in the wrong direction
3 data store to can be the only receiver
of output from a process
3 labeling incorrectly
3 data store to can be the only source
of input to a process
3 omitting data flow
© Merrill Warkentin, 2005
3 directly connecting data stores & external
entities
3 including more than 9 processes
3 having unbalanced composition
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page 6
Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Illegal Data Flows
Common DFD Errors
Dual/Split
Data Flows
Entity to Entity/Data
Store Communication
illegal data flows
B1
2.1
2.1
Entity
corrected data flows
No Data Output
B2
B1
a process is
needed to
exchange data
flows between
boundaries
B1
a process is
needed to
update (or
use) a data
store
DS1
a process is
needed to
present data
from a data
store
DS1
a process is
needed to
move data
from one data
store to
another
Entity
B1
Process
Process
Entity
D3
Data Store
B1
No Data Input
DS1
Data to Data Communication
DS1
B1
2.1
Process
D3
Data Store
D3
Data Store
DS1
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Practice Question - THINK
B1
DS2
© Merrill Warkentin, 2005
DFD for Hoosier Burger (food ordering system)
Which is an error condition?
39
DS2
DS1
Context diagram - highest view of the system
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DFD for Hoosier Burger (food ordering system)
© Merrill Warkentin, 2005
DFD for Hoosier Burger (food ordering system)
Level-1 - decomposes process 1.0 from level-0
Level-0 DFD systems major
processes, data flows,
and data stores
Level-n DFD n nested
decompositions of
sub-processes from
the level-0 diagram
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page 7
Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
DFD for Hoosier Burger (food ordering system)
DFD for Hoosier Burger (food ordering system)
Level-1 - decomposes process 4.0 from level-0
Level-2 Diagram Showing the Decomposition of Process 4.3
from the Level-1 Diagram for Process 4.0
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© Merrill Warkentin, 2005
Logical DFD
Physical DFD
3 focus on how the business operates
3 processes that exist regardless of the type
of system implemented
3 details physical system requirements
3 contains construction specifications
(software, hardware, people)
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Logical to Physical DFD
© Merrill Warkentin, 2005
Logical to Physical DFD
3 create a logical DFD of the current
system
3 add all data and processes not in
the current system which must be
present in the new system
3 derive the physical data flow
diagram for
the new system
3 logical DFD of the current system
will lead
to appropriate logical DFD of the
new system
3 physical DFD will follow naturally if
the logical DFD is accurate
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Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Logical DFD - Advantages
Physical DFD - Advantages
3 better communication
3 clarifying manual & automated processes
3 detailed process description
3 more stable systems
3 sequencing processes
3 better understanding
3 identifying temporary data stores
3 flexibility and maintenance
3 specifying name of files and printouts
3 elimination of redundancies
3 adding controls
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Partitioning Data Flow Diagrams
© Merrill Warkentin, 2005
Reasons for Partitioning
The process of separating activities into groups
based on automation, manual, and user needs
3 different user groups
3 timing
3 identify separate user groups
3 process timing
3 similar task
3 efficiency
3 data consistency
3 security
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3 similar tasks
3 efficiency
3 consistency
3 security
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Indicate with dotted line
Partitioning the DFD
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Look . . .
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page 9
Chapter 7
Process Modeling and Data Flow Diagrams (DFD)
Separate batch programs
Practice Question - THINK
Which of the following is NOT a reason
for partitioning processes into separate
programs?
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Summary
3 standard communication tool for design team
3 promotes better understanding of system
Copyright Notice
This document may not, in whole or part,
be copied, photocopied, reproduced, translated, transmitted,
or reduced to any electronic medium or machine readable form
without explicit permission and written authorization
from Dr. Merrill Warkentin.
3 ensures that all components are included
3 leads to effective logical design
mwarkentin@acm.org
http://www.MISProfessor.com
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