TCS2411 Software Engineering 1

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 outputRepresentation 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

RestaurantManager

FoodOrderingSystem

Food Order

Customer Order

Receipt

ManagementReports

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Level-1 DFD

Customer Kitchen

RestaurantManager

1. ProcessCustomer

Order

Food Order

Customer Order

Receipt

ManagementReports

2. UpdateGoods Sold

3. UpdateInventory

4. ProduceManagement

ReportsGoods SoldInventory

Goods Sold InventoryData

InventoryRecordGoods Sold

Record

Daily GoodsSold Amounts

Daily InventoryDepletion Amounts

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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 informationSink - consumer of informationExamples:

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.ProcessNew

Member

2. StudentRegistration

2.1 AcceptRegistration

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

Outsideworld Application

events behavior

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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

New state

Event causing transition

Action that occurs

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State Transition Diagram (STD)

Idle

RingingConnected

incoming call

buttonpressed

initiate answer

announcecomplete

answered announce message

hangup

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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