Data flow oriented design
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Data-Flow Oriented Design. “From DFD to Structure Chart”. 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

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Data-Flow Oriented Design

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Data flow oriented design

Data-Flow Oriented Design

“From DFD to Structure Chart”

TCS2411 Software Engineering


Lecture objectives

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


Expanding the dfd

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

Example of Level 1 DFD

Member

application form

Process

Application

new member record

Members

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Expanded to level 2

Expanded to Level 2

Member

Members

formatted

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record

application

form

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Form

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Prepare

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Format

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new

member

details

TCS2411 Software Engineering


Five step process

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

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

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Transform mapping

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

TCS2411 Software Engineering


Example of boundaries

Example of Boundaries

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application

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Afferent flow

Central

transform

Efferent flow

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First level factoring

First Level Factoring

Process

Membership

Application

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Application

Process

Application

Generate

New Member

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Second level factoring

Second Level Factoring

Process

Membership

Application

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Application

Process

Application

Generate

New Member

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New

Record

TCS2411 Software Engineering


Refinement

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

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

Example of Transaction Flow

action paths

user commands

read

user

command

invoke

command

processing

command

type

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Transaction mapping1

Transaction Mapping

transaction

control

a

reception

path

b

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dispatcher

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a

c1

p

p

q

q

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Factoring and refining

Factoring and Refining

  • Each action path has to be refined into a substructure, either by transform or transaction mapping

  • Similar to transaction flow, apply design concepts to improve quality of design

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Completing the structure chart

Completing the Structure Chart

  • For each data flow on the DFD add exactly one data couple. Use the same data flow name

  • For each control module, decide how it will control subordinates

  • For modules that select one of several paths, show selection logic with a diamond attached to the link

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Design postprocessing

Design Postprocessing

  • A processing narrative must be developed for each module

  • Interface description is provided for each module

  • Define local and global data structures

  • All design restrictions/limitations noted

  • Conduct design review

  • Optimisation is considered

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References

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

  • “The Practical Guide to Structured Systems Design” by Meilir Page-Jones, Benjamin/Cummings, 1988

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