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SysML for Systems Engineering A Model Based Approach
Jon Holt
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SysMLforSystemsEngineering Othervolumesinthisseries:
Volume1 KnowledgeDiscoveryandDataMining M.A.Bramer(Editor)
Volume3 TroubledITProjects:PreventionandTurnaround J.M.Smith
Volume4 UMLforSystemsEngineering:WatchingtheWheels,2ndEdition J.Holt
Volume5 IntelligentDistributedVideoSurveillanceSystems S.A.Velastinand P.Remagnino(Editors)
Volume6 TrustedComputing C.Mitchell(Editor)
Volume7 SysMLforSystemsEngineering J.HoltandS.Perry
Volume8 ModellingEnterpriseArchitectures J.HoltandS.Perry
Volume9 Model-BasedRequirementsEngineering J.Holt,S.PerryandM.Bownsword
Volume13 TrustedPlatformModules:Why,WhenandHowtoUseThem ArielSegall
Volume14 FoundationsforModel-BasedSystemsEngineering:FromPatternsto Models J.Holt,S.PerryandM.Bownsword
Volume15 BigDataandSoftwareDefinedNetworks J.Taheri(Editor)
PublishedbyTheInstitutionofEngineeringandTechnology,London,UnitedKingdom
TheInstitutionofEngineeringandTechnologyisregisteredasaCharityinEngland& Wales(no.211014)andScotland(no.SC038698).
† TheInstitutionofEngineeringandTechnology2019
Firstpublished2008
Secondedition2013
Thirdedition2018
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throughoutthebook
1.3Understandwhywedowhatwedoanddefineanapproach
1.4Understandtheconceptofthecommonlanguage
1.4.2Thedomain-specificlanguage
1.5Understandhowtoapplytheapproachforspecific areasofSystemsEngineering
1.6Understandhowtoimplementsuchanapproachin realorganisations
2.3TheMBSEfundamentals
2.4TheMBSEapproach
2.4.1The‘MBSEOntology’
3.1.1ProvenanceoftheMBSEOntology
3.1.2TheSystemsEngineeringBodyofKnowledge
3.1.3DisagreementswiththeMBSEOntology
3.2TheMBSEOntology
3.2.1TheSystemconcept
3.2.2TheNeedconcept
3.2.3TheArchitectureconcept
3.2.4The‘LifeCycle’concept
3.2.5TheProcessconcept
3.2.6TheCompetenceconcept
3.2.7TheProjectconcept
4.3.1Complexity
4.3.2Lackofunderstanding
4.3.3Communication
4.3.4Thevicioustriangle
4.4WhatisSysML?
4.4.1SysML’srelationshipwithUML
4.4.2AbriefhistoryofSysML
4.5.1Definingmodelling
4.5.2Thechoiceofmodel
4.5.3Thelevelofabstraction
4.5.4Connectiontoreality
4.5.5Independentviewsofthesamesystem
4.6TheSysMLdiagrams
4.7Structuralmodelling
4.7.1Addingmoredetailtorelationships 103
4.8Behaviouralmodelling
4.8.1Behaviouralmodelling–asimpleexample 108
4.9Therelationshipsbetweenbehaviouraldiagramsandstructurallevel116
4.10Identifyingcomplexitythroughlevelsofabstraction 121
4.10.1Thesystems
4.10.2Structuralview
4.10.3Behaviouralviews
4.11Chaptersummary
5TheSysMLNotation
5.1Introduction
5.1.1Diagramordering
5.1.2Theworkedexample
5.2ThestructureofSysMLdiagrams
5.2.1Frames
5.3Stereotypes
5.4TheSysMLmeta-model
5.5TheSysMLdiagrams
5.5.1Blockdefinitiondiagrams
5.5.2Internalblockdiagrams
5.5.3Packagediagrams
5.5.4Parametricdiagrams
5.5.5Requirementdiagrams
5.5.6Statemachinediagrams
5.5.7Sequencediagrams
5.5.8Activitydiagrams
5.5.9Usecasediagrams
5.6Auxiliaryconstructs
5.7Chaptersummary
6DiagrammingGuidelines
6.1Introduction
6.2Namingconventions
6.2.1Structuraldiagrams
6.2.2Behaviouraldiagrams
6.2.3Stereotypes
6.3Diagramframelabels
6.4Additionalguidelines
6.4.1Blockandinternalblockdiagrams–showinginterfaces245
6.4.2Blockandinternalblockdiagrams–showingitemflows245
6.4.3Activitydiagrams
6.4.4Defaulttoolsettings
6.5Chaptersummary
PartIIIApplications
7ProcessModellingwithMBSE
7.1Introduction
7.1.1Background
7.2Approach
7.2.1TheMBSEOntology(revisited)
7.2.2TheFramework
7.2.3TheViewpoints
viii SysMLforSystemsEngineering:AModel-BasedApproach,3rdEdition
7.3TheProcessModellingFramework 286
7.4Usingtheprocessmodellingframework 286
7.4.1AnalysingexistingProcesses 287
7.4.2Creatinganewprocessdocumentfromscratch 288
7.4.3AbstractingtacitprocessknowledgeforanewSystem289
7.4.4AbstractingtacitprocessknowledgeforanexistingSystem291
7.4.5ProcessimprovementforexistingProcesses 292
7.4.6Summary 293
7.5Chaptersummary 293 References 293
8ExpandedProcessModelling
8.1Introduction
8.1.1Background
8.2ExpandedProcessmodelling–standardsmodelling 296 8.2.1Views 297
8.2.2Summary 303
8.3ExpandedProcessmodelling–compliancemapping 303
8.3.1ProcessMappingProcess(PoMP) 305
8.3.2UsingPoMP 309
8.3.3Summary 314
8.4ExpandedProcessmodelling–competence 316
8.4.1TheexpandedMBSEOntology 316
8.4.2TheFramework 317
8.4.3Views 317
8.5ExpandedProcessmodelling–LifeCyclemodelling 328
8.5.1TheexpandedMBSEOntology 329
8.5.2Summary 342
8.6ExpandedProcessmodelling–projectmanagement 343
8.6.1TheexpandedMBSEOntology 343
8.6.2TheFramework 345
8.6.3Views 346
8.7Summary 351 References 352
9RequirementsModellingwithMBSE
9.1Introduction 353
9.1.1Background 353
9.2Approach 354
9.2.1TheMBSEOntology(revisited) 354
9.2.2TheFramework 363
9.2.3Viewpoints 365
9.3TheRequirementsmodellingFramework 399
9.4UsingtheRequirementsmodellingFramework 400
9.4.1TheACREProcess–ProcessContentView 400
9.5Summary 402 References 402
10ExpandedRequirementsModelling–SystemsofSystems
10.1.2DefiningaSystemofSystems
10.2Approach
10.2.1TheMBSEOntology(revisited)
10.2.2TheFramework
10.2.3TheViewpoints
11ArchitecturesandArchitecturalFrameworkswithMBSE
11.2.1TheMBSEOntology(revisited)
12.1Introduction
12.2AimsoftheValueChainFramework
12.3MainConcepts–theValueChainFramework’sOntology461 12.4Viewpoints
12.4.1EngagementRelationshipViewpoint
12.4.2EngagementDefinitionViewpoint
12.4.3BusinessValueViewpoint
12.4.4ContactInformationViewpoint 471
12.4.5OverviewofOntologyElementsCoveredby theViewpoints 473
12.5RulesGoverningtheuseoftheValueChainFramework 476
12.6ImplementationoftheValueChainFramework 477 12.7Summary
13.1.1Background
13.2TheMBSEArchitecturalFramework
13.2.1TheAFContextView
13.2.2TheOntologyDefinitionView
14.2.1TheSourceElementView
14.2.2TheDefinitionRuleSetView
14.2.3TheRequirementDescriptionView
14.3TheSystemofSystemsPerspective 519
14.3.1TheContextInteractionView 521
14.3.2TheValidationInteractionView 522
14.4TheLifeCyclePerspective 524
14.4.1LifeCycleView 524
14.4.2TheLifeCycleModelView 527
14.4.3InteractionIdentificationView
14.5TheProcessPerspective 531
14.5.1ProcessStructureView 531
14.5.2RequirementContextView 531
14.5.3ProcessContentView 532
14.5.4StakeholderView 533
14.5.5InformationView 533
14.5.6ProcessBehaviourView 535
14.5.7ProcessInstanceView 536
14.6TheProjectPerspective 538
14.6.1TheProgrammeStructureView 538
14.6.2TheProjectScheduleView 541
14.7TheOrganisationalPerspective 542
14.7.1TheOrganisationUnitStructureView 542
14.7.2TheOrganisationUnitInstanceView 543
14.7.3TheRankHierarchyView 545
14.7.4ThePostStructureView 546
14.7.5ThePostInstanceView 549
14.7.6ThePosttoRoleView 549
14.7.7TheMartianInstanceView 550
14.8TheCompetencyPerspective 551
14.8.1FrameworkView 551
14.8.2ApplicableCompetencyView 552
14.8.3CompetencyScopeView 553
14.9TheSystemPerspective 554
14.9.1SystemIdentificationView 555
14.9.2SystemStructureView 558
14.9.3InterfaceDefinitionView 561
14.9.4SystemConfigurationView 562
14.9.5SystemStateView 564
14.9.6SystemBehaviourView 566
14.9.7SystemInteractionView 569
14.9.8SystemParametricView 574
15BenefitsofMBSE
15.1Introduction 579
15.2‘IknowanOldLadywhoswallowedafly’ 579
15.3‘IknowanOldLadywhoswallowedaspider’ 586
15.4‘Iknowanoldladywhoswallowedabird/cat/dog’. 588
15.5‘Iknowanoldladywhoswallowedagoat/cow’ 589
15.6‘Iknowanoldladywhoswallowedahorse’ 590
16The‘People’ 593
16.1Introduction 593
16.2TheMBSEOntology(revisited) 595
16.3Teachingguide 596
16.3.1Differenttypesofteaching 597
16.3.2Professionaltraining 598
16.4Teachingaspartofanundergraduateorpostgraduatecourse600
16.4.1TeachingContext–StakeholderRolesand UseCases 600
16.4.2Agenericcoursestructure 601
16.4.3Summary 605
16.5Competence 605
16.6TheMBSEStakeholderRoles 607
16.7GenericCompetencies 613
16.7.1ExampleCompetencyScope 615
16.7.2GenericCompetencyScope–EvidenceTypes 616
16.8BespokeCompetencies 617
16.8.1ExampleCompetencyScope 618
16.8.2BespokeCompetencyScope–EvidenceTypes 619
xii SysMLforSystemsEngineering:AModel-BasedApproach,3rdEdition
16.9Genericvs.specificCompetencies 619
16.10DefiningabespokeCompetencyFramework 620
16.10.1The‘BespokeCompetencyDefinition’Process 622
16.10.2The‘BespokeFrameworkDefinition’Process 627
16.10.3Competencyassessment 629
16.11Summary 629 References 629
17The‘Process’ 631
17.1Introduction 631
17.2DefiningtheProcess 634
17.2.1TheACREProcess 634
17.2.2TheACREProcess–theProcessContentView(PCV)634
17.3UsingtheProcess 637
17.3.1Exampleuse–quickanddirtyProcess 639
17.3.2Exampleuse–semi-formalProcess 640
17.3.3Exampleuse–formalProcess 642
17.3.4Summaryofprocessimplementation 644
17.4DeployingtheProcess 644
17.4.1‘Makeprocessavailable’ 644
17.4.2‘Makeprocessaccessible’ 646
17.4.3‘Ensureawarenessofprocess’ 646
17.4.4‘Ensureappropriatepresentation’ 646
17.4.5‘Ensurevalueofprocess’ 647
17.4.6‘Providefeedbackmechanism’ 647
17.4.7‘Ensureconsistency’ 648
17.4.8‘Contributetowiderinitiative’ 648
17.5Compliancemappingwithbestpractice 648
17.5.1Automatedcompliance 653
17.6Summary 653 References 654
18The‘Tool’ 655
18.1Introduction 655
18.2ConsideringthetypesofToolsavailable 657
18.2.1The‘IndividualTool’ 658
18.2.2The‘ToolChain’ 658
18.2.3‘ToolCapability’ 660
18.2.4Summary 662
18.3UnderstandingtheNeedfortheTool 663
18.3.1Pemberton’scookinganalogy 663
18.4UsingToolswithexistingProcesses 664
18.4.1ExampleToolrealisation–quickanddirtyProcess665
18.4.2ExampleToolrealisation–semi-formalprocess 667
18.4.3ExampleToolrealisation–formalProcess 670
18.4.4GuidanceforusingTools 674
18.5ConsideringToolselection 675
18.5.1‘Providemodellingcapability’ 676
18.5.2‘Ensurecompatibilitywithmodellinglanguage’ 676
18.5.3‘Understandoperationalenvironment’ 676
18.5.4‘Provideinteroperability’ 677
18.5.5‘Ensurevendor’squalityofservice’ 677
18.5.6‘Ensurecompatibilitywiththeprocessmodel’ 678
18.5.7‘Providecapability’ 678
18.5.8‘Provideapplicationfunctionality’ 679
18.5.9‘Decideontool’ 679
18.6Toolevaluation 679
18.6.1TheMonTEProcesses 679
18.6.2MonTE–theProcessContentView 680
18.6.3InformationView 681
18.6.4ProcessInstanceView 682
18.7Summary 684
19ModelStructureandManagement 685
19.1Introduction 685
19.2Modelstructure 685
19.3Modelmanagement 688
19.3.1Versionmanagement 688
19.3.2Modelaccess 690
19.3.3Sandboxing 691
19.3.4Correctnessthroughscripting 691
19.4Chaptersummary 693 Reference 694
20ModelMaturity 695
20.1Introduction 695
20.2Maturity 695
20.2.1Technologymaturity 695
20.2.2Processmaturity 696
20.2.3Individualmaturity 697
20.3ModellingforTRLs 697
20.4Readinesslevelsformodels 699
20.5Assessmentapproach 702
20.6ApplyingModelMaturity 703
20.7Conclusions 704 References 704 Contents xiii
Authorbiographies ProfJonHoltisaninternationallyrecognisedexpertinthefieldofModel-based SystemsEngineering(MBSE).Heisaninternationalaward-winningauthorand publicspeakerandhasauthored13booksonMBSEanditsapplications.
Since2014JonhasbeenaDirectorandconsultantforScarecrowConsultants, whoare‘outstandinginthefieldofMBSE’.
JonisalsoProfessorofSystemsEngineeringatCranfieldUniversity,wherehe isinvolvedwithteachingofandresearchintoMBSE.HeisafellowofboththeIET andtheBCSandisaCharteredEngineerandCharteredITProfessional.Heis currentlytheTechnicalDirectorofINCOSEUKwhereheisresponsibleforall technicalactivitiesand,in2015,wasidentifiedasoneofthe25most-influential SystemsEngineersinthelast25yearsbyINCOSE.
JonisalsoactivelyinvolvedinthepromotionofScienceTechnologyEngineeringandMathematics(STEM)whereheusesmagic,mind-readingandoccasionalescapologytopromoteSystemsEngineeringatScienceFestivals,theIET PythagoreanCabaret,radioshowsandotherSTEMevents.Hehasalsoauthored thechildren’sSTEMbook‘ThinkEngineer’whichispublishedbyINCOSEUK.
SimonPerryhasspentover30yearsworkinginallaspectsofsoftwareand systemsengineeringandistheco-authorofeightbooksinthefieldofapplied Model-BasedSystemsEngineering(MBSE).HeistheDirectorandPrincipal ConsultantforScarecrowConsultantsLtd,providingconsultancy,trainingand conductingresearchintheapplicationofsystemsengineering.Heisamemberof theIETandINCOSE.
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PrefacetotheThirdEdition Inwriting,asinlife,sometimesprogressisthroughrevolutionandsometimes throughevolution.Whilethepreviouseditionofthisbookwassomewhatofa revolutionarychangefromthefirstedition,thisthirdeditionis,thankfully,an evolutionofthesecondedition.Muchofthecontentremainsunchanged,apartfrom correctingtheerrorsthatcreptinduringpublicationofthesecondeditionandan updatetomostofthediagramstobothreflectourcurrentSysMLtoolofchoiceand toreflectourimplementationanduseofframeworksinthetool.Wehavealsotaken thisopportunitytoupdatethechaptersontheSysMLnotationtoversion1.5ofthe language(releasedinMay2017and,atthetimeofwriting,thelatestversion)and toupdateourmodeloftheinternationalstandardISO15288toitslatestversion (publishedin2015).
Wehave,however,takenthisopportunitytoaddsomenewcontent,withnew chaptersonthebenefitsofModel-BasedSystemsEngineering,onmodelmanagement,onmodelmaturity,andonvaluechainmodelling.Inordertomakeroom forthisnewcontent,somethinghadtobedeleted,andsothreeoftheappendices fromthesecondeditionhavebeenremoved.Forthosereaderswhowouldlikethe removedappendices,theyareavailableviatheauthors’companywebsite (discoverablethroughallgoodsearchengines!).
Wehopethatyouenjoythisneweditionof‘‘SysMLforSystemsEngineering’’ asmuchasweenjoyedwritingit.
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Part1–Introduction P1.1Overview
ThispartofthebookisstructuredaccordingtothediagraminFigureP1.1.
«block» Part 1 – Introduction
«block» Part 1 – Overview
«block» Chapter 2 – Approach
«block» Chapter 1 – Introduction to Model-Based Systems Engineering
«block» Chapter 3 – MBSE Concepts
FigureP1.1Structureof‘Part1–Introduction’
Part1introducesanddescribesallofthebasicconceptsthatwillbeusedinthis book,andcomprisesthreemainchapters.
● ‘Chapter1–IntroductiontoModel-BasedSystemsEngineering’.Thischapter providesahigh-levelgeneralintroductiontothefieldofsystemsengineering, withaparticularemphasisonmodel-basedsystemsengineering.
● ‘Chapter2–Approach’.Thischapterintroducesthestandardapproachthat willbeadoptedintherestofthebookbyintroducinganddiscussingtheconceptsof‘Ontology,FrameworkandViews’.Thischapteralsocoversthe writingconventionsthatwillbeusedthroughoutthebook.
2 SysMLforSystemsEngineering:AModel-BasedApproach,3rdEdition
● ‘Chapter3–MBSEConcepts’.Thischapteridentifiesallofthekeyconcepts thatarerelevantformodel-basedsystemsengineeringandthatwillformthe backboneofeverythinginthisbook.Eachconceptisidentified,basedona numberofsourcereferences,andthendefinedintermsoftheterminologyand themeaningoftheconcept.Alloftheseconceptsarethenbroughttogetherinto theso-calledMBSEOntology.
ItisessentialtoobtainagoodunderstandingoftheconceptsintroducedinPart1 beforemovingontotherestofthebook.Itisimpossibletoimplementthe approachesandtechniquestaughtinthisbookwithoutunderstandingthechapters inthispart.
Chapter1 IntroductiontoModel-Based SystemsEngineering 1.1Introduction TheworldofSystemsEngineeringischanging.Inrecentyears,thewholefieldof SystemsEngineeringhasbeenseenasnolongeranemergingdisciplinebutasa validapproachtorealisingsuccessfulsystems.SystemsEngineeringisabroadfield thatencompassesmanydisciplines,canbeutilisedinmanyindustriesandcanbe appliedacrossmanyandvariedlifecycles.
Ifyouhavereadthisfarintothisbook(thefirsttwosentences)andfind yourselfagreeingwiththebasic,common-sensestatementsinthepreviousparagraph,thenconsiderthefollowing:
● Whatdowemeanbysystems?Forexample,technicalsystems,socialsystems andeconomicsystems.
● Whatdisciplinesdoweincludewhenwereferto‘manydisciplines’?For example,engineering,management,acquisitionandqualityassurance.
● Whatlifecyclesdowereferto?Forexample,theproductlifecycle,theproject lifecycleandtheprogrammelifecycle.
Thereareonlythreequestionshere,buttheyarecertainlysignificantones.Before progressinganyfurtherandtryingtodefinesomeofthesetermsmorefullyconsiderthatevenwiththesimplestatementsinthefirstparagraphandsubsequent threequestions,therearethreepropertiesthatcanbeappliedtoeverythingstatedso far,whichare:
● Complexity.Thereisclearlymuchcomplexityherewithregardtothenumber ofquestionsthatmaybeasked.
● Aneedforunderstanding.Whatexactlydowemeanbytheseterms?
● Aneedforeffectivecommunication.Canweconveythisinformationto interestedparties?
ThemainaimofthisbookistoaddressthesethreepropertiesofSystemsEngineeringbytheapplicationofeffectivemodelling.Infact,thiswillbejustthe startingpointaswewillthenusethesamemodellingtechniquestodriveevery aspectofsystemsengineeringthatfallswithinthescopeofthisbook.
4 SysMLforSystemsEngineering:AModel-BasedApproach,3rdEdition
Wewillbeusingmodellingto:
● Understandtheconceptsandtermsthatwillbeusedthroughoutthebook,
● Understandwhywedowhatwedoanddefineanapproach,
● Understandthecommonnotationthatwewillbeadoptingthroughoutthe book,
● UnderstandhowtoapplytheapproachforspecificareasofSystems Engineering,
● Understandhowtoimplementsuchanapproachinrealorganisations.
WhenweusethemodeltodrivethewholeapproachofSystemsEngineering,we willtermthisModel-BasedSystemsEngineeringorMBSE.WhenweapplyMBSE properly,themodelbecomesthecollectedknowledgeassociatedwiththeprojector systemand,ideally,shouldbeconsideredthesinglesourceoftruth.Theaimofthis bookisthereforetohelppeopleimplementMBSEeffectivelyandefficiently.
1.2Understandtheconceptsandtermsthatwillbeused throughoutthebook ItiscrucialforthesuccessofanySystemsEngineeringendeavourthatwecan communicateandunderstandoneanotheratabasiclevel.Oneaspectofthisis havingaclearandconcisedefinitionofallthekeyconceptsandtermsthatwillbe used.ThisisabookthatisconcernedwithMBSE,soitwouldseemappropriate thatbeforewegoanyfurtherwedefineafewbasicconcepts.Aswithmanykey conceptsinlife,thereisnosingledefinition;therefore,weshalllookatafewofthe maindefinitionsandthenabstractourownworkingdefinitionforthepurposesof thisbook.
1.2.1Systemsengineering InordertounderstandMBSE,itisimportanttohaveagooddefinitionofthe meaningofSystemsEngineering.
TherearemanydefinitionsofSystemsEngineering,allofwhichtendtodiffer dependingonthecontextofthesystemsandthepointofvieworbackgroundofthe author.Thissectionpresentsafewofthemorewidelyrecogniseddefinitionsand thendiscusseseachinturn.
ThefirstdefinitioncomesfromthelegendarySimonRamoaspartofthe AviationAuthoritySystemsEngineeringManual:
‘Systemsengineeringisadisciplinethatconcentratesonthedesignand applicationofthewhole(system)asdistinctfromtheparts.Itinvolves lookingataprobleminitsentirety,takingintoaccountallthefacetsand allthevariablesrelatingthesocialtothetechnicalaspect.’ [1]
Noticethat,inthisdefinition,thereisanemphasisonlookingatthebigger pictureandthisisbroughtupseveraltimes:‘wholesystem’,‘probleminits
IntroductiontoModel-BasedSystemsEngineering 5
entirety’and‘allthefacets’.ThisisakeyconceptinSystemsEngineering,wherea systemislookedatacrossitswholelifecycleandnotjustatonesmallpart.Also noticeherethatnon-technicalfacetsofthesystemarementionedashavingan influenceonthesystem.
ThenextdefinitioncomesfromHowardEisner:
‘Systemsengineeringisaniterativeprocessoftop-downsynthesis, developmentandoperationofareal-worldsystemthatsatisfies,inanear optimalmanner,thefullrangeofrequirementsforthesystem.’ [2]
Thereareafewconceptsintroducedherethatarenotseeninthepreviousdefinitions.Thefirstistheconceptofaniterativeprocess.Real-lifesystemsarerarely developedinalinearfashionas,evenwithwhatmaybeperceivedasalinearlife cyclemodel,forexample,therewillbemuchiterationinvolvedinsideeachstage. Thesecondinterestingpointhereisthatrequirementshavebeenmentionedforthe firsttimeinanyofthedefinitions.Indeed,thisdefinitiontalksaboutsatisfying requirements,whichmustbeoneofthebasicgoalsofanysystemsengineer.Thisis alsoqualified,however,bystatingthatthisshouldbeinanear-optimalmanner. Obviously,inanidealscenario,allrequirementsshouldbemetinanoptimum fashionbut,intherealworld,itisoftenthebestthatcanbeachievedgiventhe resourcesandtechnologyatone’sdisposal.Thisdefinitionalsoincludesarather contentiousstatementinthatthedevelopmentissaidtobe‘top-down’,whichcould beinterpretedasbeingratherlimited.
Perhaps,themostwidelyacknowledgedauthorityonSystemsEngineeringis theInternationalCouncilonSystemsEngineering(INCOSE),whichhasavery pragmaticdefinition.
‘Systemsengineeringisaninter-disciplinaryapproachandmeansto enabletherealisationofsuccessfulsystems.’ [3]
TheINCOSEdefinitionofSystemsEngineeringisrathermoretersethantheprevioustwo,yetnolessaccurate.Thisstatementsimplystateswhatmustbethe highestlevelneedforanysystemsengineer,whichistorealisesuccessfulsystems byusinganyappropriatemeansnecessary.
Thefinaldefinitionisanearlydefinitionfromthepre-SysMLdaysofmodellingfromoneoftheauthors.
‘Systemsengineeringistheimplementationofcommonsense.’ [4]
Thefinaldefinitionthatislookedathereisdefinitelyfromthe‘lessismore’ campandmakesaratherboldstatementaboutSystemsEngineeringgenerally, inthatitismostlygoodcommonsense.But,ofcourse,asanyschoolchildwill tellyou,thestrangethingaboutcommonsenseisthatitisnotatallthat common!
So,therehavebeenfourdefinitionspresentedhere,eachofwhichiscorrect, yeteachofwhichisverydifferent.Thisis,perhaps,symptomaticofadiscipline thatincludesallotherdisciplines,whichcannotbeboundedandwhichcanbe appliedtoanysysteminanydomain!
Thedefinitionthatwillbeusedforthepurposesofthisbookis:
Systemsengineeringisamulti-disciplinary,common-senseapproachthat enablestherealisationofsuccessfulsystems.
Havingestablishedthisdefinition,letusseehowmodellingfitsinwithSystems Engineering.
1.2.2Model-BasedSystemsEngineering Similartotheterm‘SystemsEngineering’therearealsoseveraldefinitionsofthe term‘MBSE’.ThefirstdefinitionistakenfromINCOSEandisarguablythemost widelyacceptedofallthedefinitionsintheworldtoday:
‘Model-basedSystemsEngineering(MBSE)istheformalizedapplication ofmodellingtosupportsystemrequirements,design,analysis,verification andvalidationactivitiesbeginningintheconceptualdesignphaseand continuingthroughoutdevelopmentandlaterlifecyclephases.’ [3]
Thedefinitionherestatesthatmodellingisusedinasupportingroleforwhat basicallyamountstoengineeringactivitieswithinthedevelopmentlifecycle.This statementisnotwrongbutitisfartoonarrowdefinitionforthepurposesofthis book.First,thestatementthatmodellingisasupportroleplaysdownthepotential impactthatmodellingcanhaveonSystemsEngineering.Themodellingshould drivetheSystemsEngineeringactivities,ratherthanmerelysupportthem.The secondpointthatthedefinitionherestatesisthattheactivitiescoverthewholeof thedevelopmentlifecycle.Again,thisistruebutnotnearlycomprehensive enough.Manytypesoflifecycleexist,suchasdevelopmentlifecycle,projectlife cycle,acquisitionlifecycle,etc.,andwecanapplyourmodellingapproachtoall ofthese.
ThenextdefinitionistakenfromJoeJenney’srecentbookonSystemsEngineeringmethods:
‘TraditionalSystemsEngineeringisamixofprosebasedmaterial,typicallyrequirementsandplans,andmodelssuchasfunctionaldiagrams, physicaldiagramsandmodediagrams.Eventuallydesigndocumentation endsindrawings,whicharemodels.MBSEcanbethoughtofasreplacing theprosedocumentsthatdefineordescribeasystem,suchasrequirementsdocuments,withmodels.Wearenotconcernedasmuchwithplans althoughplansliketestplansaregreatlyimprovedbyincludingmany diagrams,photosandothermodelswithaminimumofprose.’ [5]
Thedefinitionhereraisesafewimportantpointsbut,oncemore,doesnotgofar enough.Onepointisthatprosemaybereplacedbymodels,whichistrue,butthere seemstobeafundamentalmisunderstandingofwhatamodelishere.Thereisa suspicionherethatwhenthisdefinitiontalksaboutmodels,itreallyreferstodiagrams.Thisisthenconfirmedwiththesecondhalfofthedefinitionthatstatesthat thingscanbegreatlyimprovedbytheintroductionof‘diagrams,photosandother models’.Diagramsdonotequatetoatruemodel.Oneofthemainpointsthatwill
bemadethroughoutthisbookisthatusingdiagrams,evenwithastandardnotation suchasSysML,doesnotnecessarilyresultinamodel.
Forthenextdefinition,wereturntoINCOSE,butthistimetotheirlong-term visionforthefutureofSystemsEngineering:
‘MBSEispartofalong-termtrendtowardmodel-centricapproaches adoptedbyotherengineeringdisciplines,includingmechanical,electrical andsoftware.
Inparticular,MBSEisexpectedtoreplacethedocument-centric approachthathasbeenpracticedbysystemsengineersinthepastand influencethefuturepracticeofSystemsEngineeringbybeingfullyintegratedintothedefinitionofSystemsEngineeringprocesses.’ [6]
Thisstatement,althoughnotstrictlyspeakingadefinitionforMBSE,makesavery importantpointinmuchstrongerterms–mainly,theuseoftheterms‘modelcentric’and‘fullyintegrated’.Thisreallygoestoreinforcetheimportanceof MBSEandisfarclosertowhatweproposeinthisbook,ratherthanthatinthe originalINCOSEdefinition.
ThiswasthepredictionforMBSEthatwasmadebyINCOSEaspartoftheir 2020Vision.Fiveyearslater,aspartoftheir2025Vision,INCOSEhasthistosay:
● ‘Systemsmodellingwillformtheproduct-centricbackboneofthe digitalenterprisewhichincorporatesamodel-centricapproachto integratetechnical,programmatic,andbusinessconcerns.
● Model-basedapproacheswillextendbeyondproductmodellingto enterprise-levelmodellingandanalysis
● Toolsuites,visualizationandvirtualizationcapabilitieswillmatureto efficientlysupportthedevelopmentofintegratedcross-disciplinary analysesanddesignspaceexplorationsandoptimizations,comprehensivecustomer/marketneeds,requirements,architecture,design, operationsandservicingsolutions
● Model-basedapproacheswillmoveengineeringandmanagement frompaperdocumentationasacommunicationsmediumtoapaperlessenvironment,bypermittingthecaptureandreviewofsystems designandperformanceindigitalform
● Model-basedapproacheswillenableunderstandingofcomplex systembehaviourmuchearlierintheproductlifecycle
● Model-basedvisualizationwillallowseamlessnavigationamong relatedviewpointssuchassystem,subsystem,component,aswellas productionandlogistics
● Modelswillbeusednotonlytocapturedesignbuttoembodydesign rationalebylinkingdesigntotoplevelcustomerandprogrammatic concerns.’ [7]
NotonlyisthisalotmorediscussionconcerningMBSEbut,veryimportantly,the truescopeandpotentialofMBSEisidentifiedwhichshiftstheemphasisawayfrom simplydesigningproducts,aswasdoneinthepast,towardsanall-encompassing approachthatembracesallaspectsofthebusiness.
8 SysMLforSystemsEngineering:AModel-BasedApproach,3rdEdition
ThedefinitionofMBSEthatwillbeusedforthepurposesofthisbookis:
Model-basedSystemsEngineeringisanapproachtorealisingsuccessful systemsthatisdrivenbyamodelthatcomprisesacoherentandconsistent setofviewsthatreflectmultipleviewpointsofthesystem.
Theterm‘‘systems’’hererefersnotjusttotechnicalsystemsbutpeoplesystems, socialsystems,financialsystems,managementsystems,enterprisesystems–infact justaboutanysystemthatyoucanthinkof!
Thesedefinitionswillbeusedthroughoutthebookandwillprovidethedrive behindeverythingthatispresentedanddiscussed.
1.3Understandwhywedowhatwedoanddefineanapproach IthasbeenestablishedthatitisdifficulttopindownanexactdefinitionforSystems Engineering.However,itisnotsodifficulttopindownwhyweneedSystems Engineering.Toputitassimplyaspossible,manysystemsendinfailureordisaster.Theterm‘failure’herereferstoasystemwheretheprojectneverreached deliveryandwheretimeandmoneywerewastedbecausetimeorcostoverran.The term‘disaster’herereferstoasystemwherepeoplewerehurtortheenvironment wasdamagedasaresultofthesystemfailure.
Thefundamentalreason,therefore,whyweneedSystemsEngineeringis thatitisveryeasyforthingstogowrong,resultingindisastersorfailures.
Weneedtounderstandhowlikelyitisthatsomethingwillgowrongandthe severityoftheconsequencesofitgoingwrong.Toputthisintootherwords–we needtounderstandtherisk.
Inordertounderstandhowlikelyitisthatsomethingwillgowrong,weneedto understandwhythingsgowrong.Luckilyforus,thishasbeendonemanytimes before,andalmostalldisastersandfailurescanbeattributedtothethreeevilsof engineering,whicharecomplexity,lackofunderstandingandpoorcommunications.
TraditionalSystemsEngineeringprovidesanapproachthatcanbeappliedto minimisetherisk,suchasunderstandingrequirements,analysis,design,testing,etc.,but thisapproachitselfiscomplexandrequiresunderstandingandgoodcommunications.
Themainaimofmodelling,aswillbediscussedinmoredetailthroughoutthis book,istoaddressthesethreeevils.Wecanapplymodellingtotheprojectsand systems,ofcourse,butwecanalsoapplythemodellingtothefundamentalapproach itself,andthisformstheheartofthephilosophyofthisbookandofMBSE. TheapproachdescribedinthisbookformspartofanoverallMBSEapproach. TherearemanybenefitsassociatedwiththeapplicationofeffectiveMBSE(note theuseoftheword‘effective’here),whichare:
● Automaticgenerationandmaintenanceofsystemdocuments.Allsystem documentsmaybegeneratedautomaticallyfromthemodel,resultinginsimplerdocumentmaintenance,moreconsistentdocumentcontentanddrastically reduceddocumentationeffortandtime.
● Complexitycontrolandmanagement.Modelsmaybemeasuredand,therefore, controlled.Thismeasurementmaybeautomatedandtheresultsmaybeusedto controlandmanagethecomplexityofthemodel,hencetheprojectorsystem.
● Consistencyofinformation.Atruemodelresultsinconsistentandcoherent viewsacrossthewholesystemarchitecture.
● Inherenttraceability.Whenthemodeliscorrect,thentraceabilitybetweenall thesystemartefacts,acrossalllifecyclestages,iscontainedwithinthemodel.
● Simpleraccesstoinformation.Themodelrepresentstheknowledgeofthe projectorsystemand,asthepreviouspointmentioned,traceabilityexiststoall projectorsysteminformation.Withoutacoherentmodelknowledgeofthe systemispotentiallyspreadacrossmultiplesources,suchasheterogeneous models,spreadsheetsanddocuments.
● Improvedcommunication–language.Whenamodelisinplaceandithasbeen definedusinganestablishedmodellingnotation,thenitispossibletousethis notationasacommonlanguage.
● Improvedcommunication–conceptsandterminology.Aconsistentand coherentmodelwillhaveanunderlyingdefinitionofalltherelevantconcepts andterms,referredtolaterinthisbookasanontology,whichisusedasbasis fortheviewsthatmakeupthemodel.ThisOntologymaybethoughtofasthe domain-specificlanguage.
● Increasedunderstanding.Theveryactofmodelling,particularlywithsmall teamsofpeople,providesanexcellentwaytoachieveacommonunderstandingandobtainconsensus.
WhentryingtoselltheideaofMBSEtootherpeopleinanorganisation,itis essentialthattheabovebenefitsarerelateddirectlybacktosavingcost,timeor resources.Eachofthesepointsshouldbetailoredtoreflectthewaythatyouwork inyourorganisationtoachievethefullimpactofthebenefits.Thisisdescribedin moredetailinChapter15.
1.4Understandtheconceptofthecommonlanguage
AcommonlanguageisanessentialpartofanyMBSEendeavourasitallowspeople tocommunicatewithoneanotherinanunambiguousway.Thisisagreatideabut,in practice,oftenfailsaspeopledonotrealiseorrecognisethattherearetwoaspectsto thecommonlanguage:thespokenlanguageandthedomain-specificlanguage. Itisessentialthatweconsiderbothaspectsbeforewecanevencomecloseto havingatruecommonlanguage.
1.4.1Thespokenlanguage Whenwecommunicatewithoneanotheronadailybasis,weneedacommon spokenlanguagetoallowustotalktooneanotheratabasiclevel.Thisbook,for example,iswritteninEnglish,sohavingaworkingknowledgeofEnglishis essentialforbeingabletoreadthebookinthefirstplace.KnowingEnglish,
however,willnotguaranteethatyouwillunderstandallthetechnicaltermsinthe book,asthisrequiresadomain-specificlanguage.
ThevariousmodellingNotationsthatwehaveatourdisposalsuchasSysML, UML,etc.provideuswiththespokenlanguage,butnotthedomain-specificlanguage.Forthepurposesofthisbook,wewillbeusingtheSysML,theSystems ModellingLanguage,asourchosenspokenlanguage.Thejustificationforthe choiceofSysMLisfullydiscussedinPart2,soitwillnotbedweltonhere.In summary,SysMLisanexcellentgeneral-purposemodellinglanguagethatmaybe used,throughtheuseofadefinedsetofdiagrams,tovisualisetheviewsthatmake upthemodel.TheSysMLalsoprovidesmechanismstointegratewithothermodellingtechniquesandnotations,forexamplemathematicsandformalmethods.This meansthattheSysMLnotationdoesnotprecludetheuseofanyothernotations.
YoucanthinkofanyNotationasavisualmodellinglanguagethatcomprisesa setofDiagrams.TheDiagramsthatareavailablewilldependontheNotation,for example,SysMLhasninetypesofDiagramdefinedwhereastheUMLhas13types ofDiagramdefined.OnepointworthnotingisthateachDiagramwillrelatein somewaytotheotherDiagrams,whichprovidesconsistencyintheModel.
Consistencyiskinginmodelling.AnyNotationwillhavepre-definedsyntax, semanticsandrulesandbeunderpinnedbyitsownModelthatdefinesthese.In SysML,thisModelisreferredtoasthe‘SysMLmeta-model’whichis,justtoadd fueltothefire,definedusingUMLclassdiagrams.
ItisthisdefinitionoftheSysMLthroughitsmeta-modelthatprovidesthebasis foralloftheconsistencychecksthatwillallowustoverifythatwehaveacorrect SysMLModel.
Inonesense,itdoesnotmatterwhichNotationyouchoose,aslongasit providesthemodellingcapabilitythatyouneed,butitisimportanttochooseone.It isofcoursepossibletochoosemultipleNotations,sosomepeoplewillchoose SysMLfortheirSystemsEngineeringandUMLfortheirSoftwareEngineeringand thereisnothingwrongwiththis perse;however,themorelanguagesthatweuse, themoreweencountertheclassicTowerofBabelproblemofmultiplelanguages.
1.4.2Thedomain-specificlanguage Thespokenlanguageisessentialbutitdoesnotincludeanydomain-specificdefinitionsofterms.Inordertounderstandthis,trythissimpleexercise:talktosomeofyour English-speaking(commonlanguage)colleaguesandaskthemtodefineexactlywhat theymeanbythewords:‘‘function’’,‘‘process’’,‘‘component’’and‘‘system’’.Itis assuredthateveryonewillhaveananswer,butitisalsoverylikely(closeto100%) thatyouwillgetmorethanonedefinitionforeachterm.Trythiswithpeoplefrom differentteams,differentdivisionsinthecompanyanddifferentcompanies.
Inordertouseourspokenlanguageeffectivelyweneedadomain-specific languagethatidentifiesthetermsforeachconceptandprovidesdefinitionsforeach one.Wealsoneedtoknowhoweachoftheseconceptsrelatestooneanotherwhich willformpartofitsdefinition.
Wealsousethespokenlanguage(SysML)todefineourdomain-specificlanguage(Ontology)andwecanproduceanumberofViewsthatformtheOntology.
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A joyous home, now desolate, A circle broken, sad and lone, A vacant chair in Sable State, A husband, father, loved one gone
A widowed mother, mute with grief, Whose weeping children call in vain, Their cries and tears bring no relief, Thou can’st not meet them here again
And yet, beyond this hour of gloom, Athwart the sky, the promised bow, Above these clouds, and o’er thy tomb, The starry heavens are bending low.
In memory of loving worth, Sweet thoughts like hidden springs will flow; Rare flowers in oasis have birth, As Sorrow’s deserts verdant grow.
With patriotic, burning zeal, Thy brilliant genius, tongue and pen, Were wielded for the common weal, The good of all thy countrymen.
O’er ruins of the effete Old, Thou wrought to build a better New, Whose peerless glories might unfold, As North and South together grew.
Thou longed to note accordant band Of Sister States through future years, A Union for the world to stand With little aid of blood and tears.
Of such a spirit, He who taught Eternal Truth in Galilee; The human and divine in-wrought With perfect love and charity
And so thy deeds will grow in grace, They are exalted, wise and pure, For freedom and the human race, And in our hearts will long endure
For thee nor local, fleeting fame, But for all nations, space and time; Around thy lofty, shining name, Unfading laurels we entwine.
C R , I , Jan. 18, 1890.
G. W. L .
WHAT THE MASTER MADE. THE Master made a perfect instrument to sound His praise, It breathed forth glorious notes for many days, Chords of great strength, tones of soft melody, Grand organ anthems bird-like minstrelsy; Its final burst of music the Master’s master-stroke Fell on the world—and then the spent strings broke
M R. C .
IN ATLANTA, CHRISTMAS, 1889. I. OPROUD Gate City of the South, reborn, Risen, a phœnix, from war’s fiery flood Why draped in gloom, this precious natal morn Of Him crowned martyr for earth’s peace and good? Set in the faces of your old and young, Is seen the sorrow, ruthless Fate hath sprung!
II. Your prince lies stark amid the stately towers, Which he, strong leader in a radiant day, Had helped to build, when Georgia’s unbound powers Amazed the world and held majestic sway. G is gone, like meteor flashing bright Across the canopy of star-gemmed night!
III.
Lift him, with gentleness, and bear him hence! Keep slow, deliberate pace unto the grave Which long must be a spot where reverence, Halting its footsteps, will his laurel wave!
Impulsive youth, in halls of fierce debate, His counsels heed, his spirit emulate!
J C H , N. J. H C L .
IN MEMORY OF HENRY WOODFIN GRADY. From the “West Shore” Portland, Oregon.
AMID the wrecks of private fortunes and The fall of commonwealths, he saw arise A stricken people, and, with mournful eyes, Beheld the smoke of war bedim their land, And in its folds the fragments of a band Erst bound, as by grim Fate, to exercise Their judgments in the wrong and sacrifice Against the measures Providence had planned.
Unconquered still, he saw the Southern folk, Though awed and vanquished by the deadly jar Of war’s deep thunder belching forth, “Ye must!”
In love this Master sought to lift the yoke Of ignorance from the Southland, and to star Its night with those same stars trailed in its dust!
Unto the North he, as a brother, came, And in his heart the great warm South he brought, And as he stood and oped his mouth he wrought The miracle of setting hearts aflame, That leaped to crown him orator of fame, Since in his own emboldened hand he’d caught The golden chain of love, by many sought, To bind our Union something more than name
But hark! The while his eloquence did charm The Nation’s ear, the lightnings flashed along The wires the weeping news, “He is no more!” Brave seer! Thou didst both North and South disarm! Leap, lightnings, from your wires, the clouds among, And flash his eulogy the heavens o’er!
S , January 14, 1890.
L F .
A S O U T H E R N C H R I S T M A S
D AY.
Paraphrased from Henry W. Grady’s Editorial.
NO man or woman living now Shall e’er again behold
A Christmas day so royal clad, In robes of purpled gold, As yesterday sank down to rest, In perfect, rounded triumph in the West.
A winter day it was yet shot With sunshine to the core Enchantment’s spell filled all the scene With power unknown before And he who walked abroad could feel Its subtle mast’ry o’er him softly steal
Its beauty prodigal he saw He breathed elixir pure Twas bliss to strive with reaching hand Its rapture to secure, And bathe with open fingers where The waves of warmth and freshness pulsed the air
The hum of bees but underrode The whistling wings outspread Of wild geese, flying through the sky, As Southwardly they sped— Whil b d l i d t
While embered pale, in drowsy grates, The fires slept lightly, as when life abates.
And people, marveling, out of doors, Watched in sweet amaze
The soft winds’ wooing of delight, Upon this day of days
Their wooing of the roses fair Their kissing lilies, with a lover’s air.
God’s benediction, with the day, Slow dropping from the skies, Came down the waiting earth to bless, And give it glad surprise
His smile, its light a radiant flood, That upward bore the prayer of gratitude
And through and through its stillness all And through its beauty too
To every heart came mute appeal, To live a life more true— And every soul invoking then, With promise—“Peace on earth—good will to men.”
IN MEMORY OF HENRY W. GRADY. SHALL we not mourn for those who pass Like meteors from the midnight sky, From out the gleaming heights of fame, As those who for their country die?
Who die, and sleep in dreamless slumber, Where sunbeams like a blessing shed Their glories, and the rain-drops, falling, Weep ever o’er our Southern dead
Of silvery tongue, and heart of fire, And grace of manhood, what is left? A voiceless grief a tear a sigh, A nation of her son bereft
Great soul with eloquence o’erflowing, In rhythmic measures sweet and grand, Great heart whose mission was a message Of peace and good will, thro’ the land
O tongue of flame by truth inspired! Tho’ thou art silent, and we never May hear again thy stirring strains, They’ll echo in our halls forever.
Thy life was like a rushing river, That proudly bore upon its breast Our highest hopes unto a haven, Where heroes dwell, and patriots rest.
Sleep well! tho’ thou art gone, the grave Holds but the outward earthly shrine, That held within its clay-cold breast The sacred spark of life divine.
Sleep well! immortal, unforgotten, Where buds and blossoms round thee blow, And the soft fires of Southern sunsets In glory gild thy couch below.
E
J. H .
D , T
HENRY W. GRADY. IF Death had waited till the grateful Land He championed with his life had bent and crowned, With a proud, civic garland of command
That knightly brow, with laurels freshly bound! Yet he cared not for crowds this wrestler strong; If down the arena swept some warm, wild breath Of his People’s praise—this bore his soul along, This came with sweetness in the midst of death, For love was more to him than crown or wreath.
Ah! half her Sun is stricken from the South, Since he is dead her tropic-hearted one, Will the pomegranate flower’s vivid mouth Open to drink the dews when Frost is done? Will the gay red-bird flash like winged flame, The mocking-bird awake its thrilling lyre? Will Spring and Song will Love ev’n seem the same, Now he is gone the spirit whose light and fire And pulsing sweetness were like Spring to make, The gray earth young? will Light and Love awake, And he still sleep? and we weep for his sake!
M E. B .
THE OLD AND THE NEW. NOT to the beauteous maid who weeps And wails in broken numbers, Where ’neath the solemn cypress sleeps The brave in dreamless slumbers
Oh, not to her whose pallid cheeks With form all bent and broken An utter loss of promise speaks And perished hopes betoken
Ah, not to her!—the sorrowing maid Who sighs so sad and lowly, Where our “Lost Cause and Cross” were laid, Keeping their memories holy.
Ah, not to her whose sons have passed To rest in peace sedately, To glory and the grave at last, In soldier phalanx stately;
That sleep beneath the mountain sod Or by the murmuring rivers, Beneath the blooming prairie clod Or where the sea breeze quivers.
The past is God’s, the future ours, And o’er our plains and mountains The young spring comes with thousand flowers And music in bright fountains.
