TCS2411 Software Engineering1 Data-Flow Oriented Design “From DFD to Structure Chart”

TCS2411 Software Engineering2 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 Engineering3 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

TCS2411 Software Engineering4 Example of Level 1 DFD Process Application Member application form Members new member record

TCS2411 Software Engineering5 Expanded to Level 2 Get Form Check Form Assign Code Format Record Prepare Record Member Members application form application details checked application details new member record new member details formatted new member record

TCS2411 Software Engineering6 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

TCS2411 Software Engineering7 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 Transaction flow

Transform Mapping

Factoring

TCS2411 Software Engineering11 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 Engineering12 Example of Boundaries Get Form Check Form Assign Code Format Record Prepare Record Member Members application form application details checked application details new member record new member details formatted new member record Afferent flowEfferent flowCentral transform

TCS2411 Software Engineering13 First Level Factoring Get Application Process Application Generate New Member Process Membership Application

TCS2411 Software Engineering14 Second Level Factoring Check Application Process Application Generate New Member Process Membership Application Get Application Get Application Form Format New Record Generate New Record

TCS2411 Software Engineering15 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

TCS2411 Software Engineering16 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

TCS2411 Software Engineering17 Example of Transaction Flow read user command invoke command processing user commands command type action paths

TCS2411 Software Engineering18 Transaction Mapping b d a c1 qp transaction control dispatcher a p b d q reception path

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 read command validate command determine type read record calculate output values format report produce error msg read fixture status determine setting format setting send control value command invalid command error msg status combined status raw setting fixture setting robot control start/stop assembly record values report valid command

Map the Flow Model

Refining