Software Design 2e - DIM

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13.3 The SSA/SD process263As already mentioned in Section 13.1, in its original form the over-arching strategyadopted in this method can be regarded as a refinement of the classic top-downstrategy of ‘divide and conquer’ discussed in Chapter 11. The designer begins byconstructing a model of the top-level problem in terms of the operations that areperformed by the system, and then this description of the problem is transformed intoa plan for a program; this plan is in turn described in terms of the set of subprogramsthat are used to perform the relevant operations, together with the details of the interactionsbetween the subprograms.The form of the design process is more subtle than that of the simple top-downdesign strategy, however: it extends the simple description of the system, expressed interms of operations, by also considering the flow of information between the operations.The wider foundation that this provides assists the designer in producing a moreconsistent structure for the eventual design than is likely to arise from the use of thesimple top-down strategy, since the information-flow component of the model helps toreduce and constrain the ‘solution space’ available to the designer.Returning to the framework that is provided by the transformational model of thedesign process introduced in Chapter 9: the design transformations involved in thismethod can be viewed as forming a set of sequential steps, with feedback occurringautomatically between them. The five basic steps, shown in Figure 13.5, are:The SSA/SD process1. Construct an initial DFD to provide a top-level description of the problem (the‘Context Diagram’).2. Elaborate this into a layered hierarchy of DFDs, supported by a data dictionary.3. Use Transaction Analysis to divide the DFD into tractable units.4. Perform a Transform Analysis on the DFD created for each transaction, in orderto produce a Structure Chart for that transaction.5. Merge the resulting Structure Charts to create the basic implementation plans,and refine them to include any necessary error-handling, initialization, and otherexceptions.Steps 1 and 2 are essentially those that make up the process that we are terming‘Structured Systems Analysis’, while the other three can be considered as forming theprocess of Structured <strong>Design</strong>. This section concentrates on describing the nature of thefirst four steps, since the actions of step 5 do not involve major design decisions,although they play an important role in the form of the final design. (To do properjustice to the actions of step 5 also requires a more detailed description than can beprovided in an overview such as this.)13.3.1 Steps 1 and 2: Structured Systems AnalysisMost of the basic operations involved in these steps were outlined in Section 7.2.1,when discussing the use and the development of the DFD. However, as StructuredSystems Analysis is quite a large topic, which merits textbooks in its own right, it isappropriate to add a few more comments at this stage.
264Structured systems analysis and systems designFigure 13.5Transformation diagram for SSA/SD.
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Software Design
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Software DesignDavid Budgen
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viContentsChapter 4 Design Qualitie
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viiiContentsChapter 16 Designing wi
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xPreface to the second editiondescr
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xiiPreface to the First EditionWhy
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xivPreface to the first editionto t
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xviPublisher’s AcknowledgementsWe
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chapter 13The Nature of the Design
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Design is just as important with so
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Initialobservations7More systematic
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development. However, it should als
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From this relatively simple case st
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nnWhere possible, the panels used i
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It might well be argued that while
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system being developed. Clearly, in
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case study, the outline plan on squ
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nnnWicked problems do not have an e
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on to Pittsburgh. Airline B is the
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262.1 What is software?The software
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28nChangeability. Software suffers
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30The software design processFigure
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32The software design processthat a
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38The software design processproces
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40The software design processform p
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44The software design process2.3 De
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463.1 A context for designDesign in
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48Design in the software developmen
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54A personal itchDesign in the soft
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60nthe associated role of requireme
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chapter 463Design Qualities4.1 The
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is virtually impossible to modify i
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measurable characteristic that can
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69Assessing design qualityFigure 4.
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nnnnreliabilityefficiencymaintainab
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Table 4.1The cognitive dimensions73
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system. The results of this study u
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nnnmodules are easy to replace;each
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Table 4.3The principal forms of coh
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Identifying attributes that are the
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Our study of the nature of the desi
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nTechnical design reviews can provi
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chapter 589Describing a Design Solu
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91Figure 5.1Example of a ‘physica
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term is used to describe ‘stakeho
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95Design viewpoints for softwareFig
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nnof mark-up languages such as HTML
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nnntextdiagramsmathematical express
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happens with pioneering ideas, it h
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I have termed ‘derived viewpoints
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1066.1 The need to share knowledgeT
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108Transferring design knowledge6.1
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110then briefly consider how the co
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112Transferring design knowledgethe
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114Transferring design knowledge6.2
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116mainTransferring design knowledg
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118Transferring design knowledgennn
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120Transferring design knowledgeOne
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1226.5 A unified interpretation?Tra
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124Transferring design knowledgeA s
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chapter 7127Some Design Representat
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Table 7.1The selection of black box
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131Black box notationsFigure 7.1A f
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133Black box notationsFigure 7.3mac
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135Black box notationsFigure 7.4A
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nattributes are classes of values t
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The ERD viewpointERDs are purely an
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7.2.4 The StatechartLike the STD th
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145Black box notationsFigure 7.13St
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7.2.5 The Jackson Structure Diagram
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149Black box notationsFigure 7.17 A
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153Figure 7.21The UML class notatio
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155Use case (title indicates the ac
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157cardrejectedprocesscardcard acce
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159White box notationsFigure 7.27A
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only the presence of the latter is
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In its most simple form, such a com
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NarrativeUser starts web browserUse
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If anything, pseudocode is used rat
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Many notations can be conveniently
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171Developing a diagramFigure 7.38E
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Stevens P. with Pooley R. (2000). U
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chapter 8175The Rationale for Metho
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provide a methodological analysis o
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179Figure 8.2nnSome properties of f
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ones that may be usefully supported
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183Figure 8.3The use of virtual mac
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In particular, the use of a design
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need to be recognized. Unfortunatel
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A somewhat different approach to cl
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Exercises1918.1 How would you class
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1949.1 The role of strategy in meth
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196Design processes and design stra
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Page 229 and 230: 212ExercisesDesign processes and de
Page 231 and 232: 21410.1 Design by template and desi
Page 233 and 234: 216Design patternspatterns for obje
Page 235 and 236: 218Design patternsFigure 10.1A simp
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Page 256: Further reading239Wirth N. (1971).
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Page 263 and 264: 246Incremental designpossible model
Page 265 and 266: 248Incremental designnnthe roles, r
Page 267 and 268: 250Incremental designFunctionalityT
Page 269 and 270: 252Incremental designBusinessstudyF
Page 271 and 272: 254Incremental designalthough it ma
Page 273 and 274: 256ExercisesIncremental design12.1
Page 275 and 276: 25813.1 Origins, development and ph
Page 277 and 278: 260Structured systems analysis and
Page 279: 262Structured systems analysis and
Page 305 and 306: 288ExercisesStructured systems anal
Page 307 and 308: 29014.1 Some background to JSPJacks
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chapter 15315Jackson System Develop
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317The JSD modelFigure 15.1Top-leve
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319Figure 15.3Generic form of ESD.t
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321Figure 15.6Process 1.The SSD for
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323The JSD processFigure 15.9 The J
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Entity analysis (the entity-action
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327The JSD processFigure 15.13The J
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329The JSD processFigure 15.14 The
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331The JSD processFigure 15.15 The
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333The JSD processFigure 15.16The c
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Information function step335From a
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The situation is analogous to that
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Exercises33915.1 Construct an ESD t
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34216.1 The ‘object concept’Des
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344Designing with objectsThe evolut
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346Designing with objectsFigure 16.
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348Designing with objectsFor the ob
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352 Executable units of code(subpro
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354A summary of the core concepts o
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356Designing with objectsnnnnnnnorg
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358Designing with objectsA rather l
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360Designing with objects16.2.1 Sur
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364closely at the representation pa
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366Designing with objectsAn empiric
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368Designing with objectsof a frame
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370Designing with objects16.3.2 Des
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372Designing with objectsDepartment
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376Designing with objects1. The obj
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378Designing with objectsdescribe a
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380Designing with objectsnnapproach
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382Designing with objectssequence d
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384Designing with objectsnnhow is t
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386step, it is those analysis-relat
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388Designing with objectsStep 7: De
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390Designing with objectsbehaviour,
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392indicate the degree of effort. A
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394Designing with objectsThe UP wor
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398Designing with objectsSimilarly,
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400Designing with objectswww.omg.or
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40217.1 The component conceptCompon
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404Component-based designmore than
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406Component-based designFigure 17.
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408Component-based designto address
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410Component-based designnto decomp
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412Component-based design4. Archite
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41417.3 Designing componentsCompone
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416Component-based designSourceInde
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418Component-based designwww.sei.ed
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42018.1 The case for rigourA formal
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422A formal approach to designmight
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424A formal approach to designFigur
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426A formal approach to design18.2.
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428 Table 18.1 Set operations used
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430A formal approach to designClear
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432InitResSystA formal approach to
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438A formal approach to designThis
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44018.2 Write simple Z specificatio
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44219.1 What is software now?Whithe
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444Whither software design?Figure 1
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446Whither software design?Figure 1
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448Whither software design?Another
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451BibliographyAbbott R.J. (1983).
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Buxton J. and McDermid J. (1992). H
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Guindon R. (1990). Designing the de
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Perry D.E. and Wolf A.L. (1992). Fo
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Ward P.T. and Mellor S.J. (1985). S
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462IndexCcall and return (architect
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464Indexgraphical user interface (G
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466Indexprogram design 290program i
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468WYIndexwalkthrough 81waterfall m
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