Functional and
Behavioural Modeling
“What is the software supposed to do?”
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Lecture Objectives
To illustrate the modeling of functional
and behavioural characteristics of the
problem domain
To describe the elements of data flow
diagrams and the associated rules for
drawing them correctly
To describe the elements and usage of
state transition diagrams
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Functional Modeling
In understanding the requirements of the
software, the functions required by the
customer will be identified
All the functions process information in
some way in the system
Basically input  process  output
Representation of how information is
transformed
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Data Flow Diagram
(DFD)
Graphical representation of functional
modeling
In analysis, provide representation of
information flow in existing and required
system
In design, the DFDs can be decomposed
into lower level processes (sub-systems)
for implementation
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Context Diagram
Customer
Receipt
Customer Order
Food
Ordering
System
Kitchen
Food Order
Management
Reports
Restaurant
Manager
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Level-1 DFD
Customer Order
Customer
Receipt
Goods Sold
1. Process
Customer
Order
2. Update
Goods Sold
Goods Sold
Record
Goods Sold
Daily Goods
Sold Amounts
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Kitchen
Food Order
Inventory
Data
3. Update
Inventory
4. Produce
Management
Reports
Management
Reports
Inventory
Record
Daily Inventory Inventory
Depletion Amounts
Restaurant
Manager
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External Entity
A producer or consumer of information
that resides outside the bounds of the
system to be modeled
Source - producer of information
Sink - consumer of information
Examples:
Customer
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Supplier
Management
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Process
A transformer of information (a function)
that resides within the bounds of the
system to be modeled
Examples:
1.Process
New
Member
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2. Student
Registration
2.1 Accept
Registration
Details
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Data Flow
Data object that flows in the system; the
arrowhead indicates the direction of data
flow
new student record
student record
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Data Store
A repository of data that is to be stored
for use by one or more processes
May be as simple as a buffer or queue or
as sophisticated as a relational database
Examples:
Students
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Inventory
Courses
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DFD Rules
Process
No process can have only outputs.
No process can have only inputs.
A process has a verb label.
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DFD Rules
Data Store
Data cannot move directly from one data
store to another data store.
Data cannot move directly from an outside
source to a data store.
Data cannot move directly to an outside sink
from a data store.
A data store has a noun phrase label.
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DFD Rules
Source/Sink
Data cannot move directly from a source to a
sink. It must be moved by a process if the
data are of any concern to our system.
A source/sink has a noun phrase label.
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DFD Rules
Data Flow
A data flow has only one direction of flow
between symbols.
A fork in data flow means that exactly the
same data goes from a common location to
two or more processes/stores/sources/sinks.
A join in a data flow means that exactly the
same data comes from any two or more
processes/stores/sources/sinks.
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DFD Rules
Data Flow (continued)
A data flow cannot go directly back to the
same process it leaves.
A data flow to a data store means update.
A data flow from a data store means retrieve
or use.
A data flow has a noun phrase label. More
than one data flow noun phrase can appear
on a single arrow.
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DFD Characteristics
Can be used to model physical or logical,
current or new systems
Does not represent procedural or timerelated processes
Revisions to the same DFD are done to
improve model based on understanding
Decision to stop iterative decomposition
may be difficult
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Behavioural Modeling
events
Outside
world
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behavior
Application
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Behavioural Modeling
Representation of how the system
changes and the events that cause the
changes to happen
Also represent actions that may be taken
as consequences of events
Graphically drawn as state transition
diagram
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State Transition
Diagram (STD) Notation
State
Event causing transition
Action that occurs
New state
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State Transition
Diagram (STD)
announce
complete
hangup
button
pressed
Idle
incoming call
initiate answer
Connected
Ringing
answered announce message
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State Transition
Diagram Elements
State - any observable mode of behaviour
represented as a node in STD
State transition - change of one state to another
caused by an event
represented as labeled arrow in STD
label is the event causing the transition
Event - external or internal occurrence that has
an effect on the system
Action - process taken as response to event
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References
“Software Engineering: A Practitioner’s
Approach” 5th Ed. by Roger S. Pressman,
Mc-Graw-Hill, 2001
“Software Engineering” by Ian Sommerville,
Addison-Wesley, 2001
“Modern Systems Analysis and Design” by
Jeffrey A. Hoffer, Joey F. George & Joseph
S. Valacich, Benjamin/Cummings, 1996
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