tcs2411 software engineering1 data-flow oriented design “from dfd to structure chart”

TCS2411 Software Engineering 1

Data-Flow Oriented Design

“From DFD to Structure Chart”

TCS2411 Software Engineering 2

Lecture Objectives

• To describe the process of translating the DFDs to structure charts

• To understand the systematic approach in producing the design from the analysis model

• To understand the different types of conversion that can be done in producing the structure chart

TCS2411 Software Engineering 3

Expanding the DFD

• Initial analysis produces the Context Diagram and Level 1 DFD

• In the design phase, the DFD is expanded to lower levels, giving more sub-processes within the original process

• Level 1 Level 2 Level 3 …• Consistency is to be maintained from level to

level

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Example of Level 1 DFD

ProcessApplication

Member application form

Members

new member record

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Expanded to Level 2

GetForm

CheckForm

AssignCode

FormatRecord

PrepareRecord

Member Members

applicationform

applicationdetails

checkedapplicationdetails

newmemberrecord

newmemberdetails

formattednew memberrecord

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Five-Step Process

• The type of information flow is established• Flow boundaries are indicated• The DFD is mapped into program structure• Control hierarchy is defined by factoring• Resultant structure is refined using design

measures and heuristics

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Types of Information Flow

• Transform Flow– Information enter at a point, transformed, and

exit at another point– Path: incoming flow central transform outgoing

flow• Transaction Flow

– Single data item, transaction, triggers one of many paths

– Path: incoming flow transaction centre action path

Flow Characteristics

Transform flow

Transactionflow

Transform Mapping

data flow model

"Transform" mapping

ab

c

d e fg h

ij

x1

x2 x3 x4

b c

a

d e f g i

h j

Factoring

typical "worker" modules

typical "decision making" modules

direction of increasing decision making

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Transform Mapping

• After transform flow is identified, identify the boundaries of incoming and outgoing flow

• Incoming flow = Afferent flow• Outgoing flow = Efferent flow• In between the boundaries of the two is the

central transform

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Example of Boundaries

GetForm

CheckForm

AssignCode

FormatRecord

PrepareRecord

Member Members

applicationform

applicationdetails

checkedapplicationdetails

newmemberrecord

newmemberdetails

formattednew memberrecord

Afferent flow Efferent flowCentraltransform

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First Level Factoring

GetApplication

ProcessApplication

GenerateNew Member

ProcessMembershipApplication

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Second Level Factoring

CheckApplication

ProcessApplication

GenerateNew Member

ProcessMembershipApplication

GetApplication

GetApplication

Form

FormatNew

Record

GenerateNew

Record

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Refinement

• The hierarchy produced is then refined to improve the quality of the design

• Modules could be exploded or imploded• Apply design concepts of module

independence, good cohesion, minimal coupling, and ease of maintenance

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Transaction Mapping

• If transaction flow is identified, identify the transaction centre and flow characteristics of each action path

• Similar to transform flow, boundaries are identified for incoming flow and the separate action paths

• Each action path is a transform flow or transaction flow as well

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Example of Transaction Flow

readuser

commandinvoke

commandprocessing

user commands

commandtype

action paths

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Transaction Mapping

b d

a c1

qp

transactioncontrol

dispatcher

a

p

b

d

q

receptionpath

Transaction Mapping

a

b

t

g

h

d

e

f

i

k

j

l

m

n

Data flow model

x1

b

a

t

x2 x3 x4

d e f g h x3.1 l m n

i j

k

mapping

program structure

Isolate Flow Paths

readcommand

validatecommand

determinetype

readrecord

calculateoutputvalues

formatreport

produceerror msg

readfixturestatus

determinesetting

formatsetting

sendcontrolvalue

command

commandinvalid command

error msg

status

combinedstatus

raw setting

fixture setting

robot control

start/stop

assemblyrecord

record

values

report

valid command

Map the Flow Model

process operator

commands

command input

controller

read command

validate command

produce error

message

determine type

fixture status

controller

report generation controller

send control value

each of the action paths must be expanded further

Refiningprocess operator

commands

command input

controller

read command

validate command

produce error

message

determine type

send control value

read fixture status

determine setting

format setting

read record

calculate output values

format report

fixture status

controller

report generation controller