Flow-oriented modeling represents how data objects are transformed as they move through a system. A data flow diagram (DFD) is the diagrammatic form used to depict this approach. DFDs show the flow of data through processes and external entities of a system using symbols like circles and arrows. They provide a unique view of how a system works by modeling the input, output, storage and processing of data from level to level.

1. Flow-Oriented Modeling
Represents how data objects are transformed at they
move through the system
A data flow diagram (DFD) is the diagrammatic form
that is used
Considered by many to be an ‘old school’ approach, flow-
oriented modeling continues to provide a view of the
system that is unique—it should be used to supplement
other analysis model elements
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2. The Flow Model
Every computer-based system is an
information transform ....
computer
input based output
system
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3. Flow Modeling Notation
external entity
process
data flow
data store
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4. External Entity
A producer or consumer of data
Examples: a person, a device, a sensor
Another example: computer-based
system
Data must always originate somewhere
and must always be sent to something
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5. Process
A data transformer (changes input
to output)
Examples: compute taxes, determine area,
format report, display graph
Data must always be processed in some
way to achieve system function
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6. Data Flow
Data flows through a system, beginning
as input and be transformed into output.
base
compute
area
triangle
height area
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7. Data Stores
Data is often stored for later use.
sensor #
sensor #, type,
look-up location, age
sensor
report required data
type,
location, age
sensor number
sensor data
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8. Data Flow Diagramming
Guidelines
• All icons must be labeled with meaningful names
• The DFD evolves through a number of levels of
detail
• Always begin with a context level diagram (also
called level 0)
• Always show external entities at level 0 and 1
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9. • The level 0 data flow diagram should depict the
software/system as a single bubble
• Primary input and output should be carefully
noted
• Refinement should begin by isolating candidate
processes, data objects, and data stores to be
represented at the next level
• All arrows and bubbles should be labeled with
meaningful names
• Information flow continuity must be maintained
from level to level
• One bubble at a time should be refined
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10. Constructing a DFD – level 0
• Review the data model to isolate data
objects and use a grammatical parse to
determine “operations”
• Determine external entities (producers
and consumers of data)
• Create a level 0 DFD
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13. Constructing a DFD – level 1
• A “grammatical parse” on the narrative that
describes the context level bubble.
• Isolate all nouns (and noun phrases) and verbs
(and verb phrases).
• Verbs are processes which are represented as
bubbles in a subsequent DFD.
• Nouns are external entities / data objects /
control objects / data store.
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15. Constructing a DFD – level 2
• Refines the monitor sensors process
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17. PSPEC
• The process transform performs password validation at the control panel
for the SafeHome security function.
• Process password receives a four-digit password from the interact with
user function.
• The password is first compared to the master password stored within the
system.
• If the master password matches , [valid id message = true] is passed to the
message and status display function.
• If the master password does not match , the four digits are compared to a
table of secondary passwords (they may be assigned to house guests
and/or workers who require entry to the home when the owner is not
present).
• If the password matches an entry with the table, [valid id message = true]
is passed to the message and status display function.
• If there is no match, [valid id message = false] is passed to the message
and status display function.
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