Functional and Behavioural Modeling

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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
Kitchen
Customer Order
Food Ordering System
Receipt
Food Order
Management Reports
Restaurant Manager
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Level-1 DFD
Customer
Kitchen
Customer Order
1. Process Customer Order
Food Order
Receipt
Inventory Data
Goods Sold
2. Update Goods Sold
3. Update Inventory
Inventory Record
4. Produce Management Reports
Goods Sold Record
Inventory
Daily Inventory Depletion Amounts
Goods Sold
Daily Goods Sold Amounts
Management Reports
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
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
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
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 time-related
  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
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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)
Idle
announce complete
hangup
incoming call
button pressed
initiate answer
Ringing
Connected
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 Practitioners 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