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Modeling Formalism(Modeling Language Foundations)
SystemModeling Assessment & Roadmap WorkingGroup Meeting – SE DSIGReston – March , 2016Yves BERNARD
Motivations
Drivingrequirement #2.Thenext-generation modeling language must include precise semantics that avoid ambiguity and enable a concise representation of the concepts.The language mustderive from a well-specified logical formalism that can leverage the model for a broad range of analysis and model checking.Thisincludes the ability to validate that the model is logically consistent, and the ability to answer questions such as the impact of a requirement or design change, or assess how a failure could propagate through asystem.Thelanguage and tools must also integrate with a diverse range of equation solvers and execution environments that enable the capture of quantitative data.
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Evaluation criteria
Precision/unambiguity:ability to have only one (official/standard) semantic interpretationUsability:easinesstolearn (i.e. average learning curve),tooperate (e.g. number of clicks/inputs for basic operations)Efficiency:conciseness, (i.e. telling more with less)Interoperability:ability to be read and use by analysis tools
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SysMLv2 Services
Will contribute to the following services (as defined by the “SysMLv2 Services spreadsheet”):Create, view, update, delete, and execute model transformations to/fromSysMLmodelsDefine, update, delete, and execute model queries to support visualization andanalysisDefine, update, delete, and execute model validation rules to validate input data and modelDefine, transform, and execute analytical models
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Illustration with HybridSUV Change Scenario
Vehicledesign unable to meet a requirement (e.g., stopping distance, safety, stability)Analysis capabilities able to provide evidence of such a statementProposerequirementchange / assess potential impactComputation of potential impacts of this change on the designProvidecapabilities for both static analysis and simulationProposeupdate to systemdesignAbility to compute differences between “as is” and “to be” designImplement/update designAutomated (HW/SW) code generation, and other M2T/M2M transformationVerifysystem meetsrequirementProvide capabilities for both static analysis and simulation
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La Jolla meeting outcomes
Logics formalism worth to be considered:Temporallogics(=> causalmodel of time,i.e. events ordering)Highlevel formalism based on FOL (e.g. Petri-Nets, state machines, …).andtheCategory theory (which expand the Set theory) as well.Ability to allow for a variable level of formalism (i.e. just like compiler error levels)About evaluation criteria:Levelof training required for using formallanguages (as partof the usabilitycriterion)effort/costrelated to the implementation of the language. Linked to technology readiness/maturityaspect.Computingpower required to operate the language as expectedTo be clarified:“evaluation criteria” versus “requirements”
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New / Updated
Requirements vs Evaluation Criteria
DefinitionsAnevaluation criterionspecifies a quantitative characteristic of interest(“property”) whichcan be assessed. Its value may be parametric (i.e. numerical) or not.Arequirementis a statement about one thing. Evaluating a thing against a requirement results in a Boolean value depending on whether the corresponding statement is true or false for that thing. A requirement may refer on an evaluation criterion.
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New / Updated
Evaluation criteria computation rules
Precision/unambiguity:ability to have only one (official/standard) semantic interpretation% of the language elements that have one and only one possible interpretation.Usability:easinesstolearn (i.e. average learning curve)Number of concepts (i.e.metaclasses) / a reference number (TBD, e.g.:nbof reserved words in the C programming language,nbof entries in the SE glossary…)Efficiency:conciseness, (i.e. telling more with less)Number of model elements to represent a set of system aspects used as a benchmarkInteroperability:ability to be read and use by analysis tools@Pawel: to provide input on this
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New / Updated
Modeling Language properties
Related to execution capabilitiesAbilitytoqualify and describe data and data structure (i.e. metadata)Ability to specify values(i.e. data)Ability to specify state/value changes (including functions as y=f(x))Ability to specify sequences of changeAbility to specify data flows among changesAbilityto specifycontrol structures of change sequencesNote: a wider set of control structures will have a positive impact on theefficiencybut may reduce theusabilityRelated to logical inference capabilitiesAbility to specify categorical statementAbility to specify ternary relationships among them (i.e. syllogism)Ability to consider empty categories
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Behaviorsemantics
New / Updated
Annex
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About Language Syntax and Semantics
Extracted fromfUML:“A formal language only attaches meaning to statements that are correctly constructed orwell formed. Thesyntaxofthe languageprovides the rules for how to construct well-formed statements or, equivalently, for validating that aproposed statementis actually well-formed. Thesemanticsof the language then provides the specification of the meaning ofwell-formed statements.”
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New / Updated
SysML (UML)
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CurrentSysMLdefinition and its limitations
Based on UML 2.5, defined as a profile, i.e. has limited extension capabilitiesNot fully compliant to UML 2.5 Profile specificationthese extension capabilities seem to be unsufficientNot executableanalyses require specific extension (i.e. non standard)Design for supporting diagram, rather than analysis: expectation on modeling have changedMBSE requires more than creating diagrams
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Proposal for formalism specification in the RFP
Option 1: based on “compilation” approach (cf. Cambridge meeting’s presentation)Other option?
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Foundation Candidates
First OrderLogicsBasis for defining axioms on which analyses can be builtused byfUML(bUMLbase semantics)No intrinsic support for timeTemporal LogicsAdd modes related to timeBetter support of evolving systems (i.e. behaviors)Description Logics (ontologies, processes)Knowledge representation, based of FOLNote: support for time is part of thefUMLroadmap
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