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Integration of SysML and Modelica: Semantics, Connectors, and Compatibility

This report discusses the integration of SysML and Modelica, focusing on the semantics of ports and connectors. It provides an overview of the initial draft document and explores the generation of SysML constructs that fit within the profiling mechanism. The report also examines the compatibility between the two languages and proposes different approaches for model integration.

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Integration of SysML and Modelica: Semantics, Connectors, and Compatibility

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  1. SysML-Modelica IntegrationWorking Group Report(SE DSIG meeting, Washington DC 3/24/2009) Chris ParedisGeorgia Tech

  2. Agenda • Introductions • Getting Organized • Quick overview of initial draft document • Discussion of Chapter 1 • Semantics of ports and connectors • Mock-ups for SysML equivalent of spring-mass system

  3. Getting Organized • Practical issues • Regular meeting slot: Wed at 10AM Eastern • Conference call facilities? • Wiki • http://www.omg.org/members/sysml-rtf-wiki/doku.php?id=rtf2:groups:sysml_and_modelica_integration(requires regular OMG password)

  4. WG Focus and Scope • Focus: • Reuse Modelica syntax by Integrating Modelica into SysML • Integrating parts of SysML into Modelica may also be worth considering, but is outside the scope of this exercise • Scope: • Cover the Modelica constructs needed for the Modelica Standard Library to be used in SysML • Generate corresponding SysML constructs that fit within the profiling mechanism

  5. Overview of Draft Document

  6. Main Question: Which Diagram Type? Rotational Energy Flow • All three SysML diagrams share the same high-level structure • Composition of “port-based” objects • Connections between “ports” • Hierarchical: composition and “port” delegation RealInput Connector Signal Connection

  7. Semantics of Modelica Connectors • 2 basic types: causal and acausal • Causal: • defined as input or output • Acausal: • defined as flow or nonflow (must appear in pairs of flow and nonflow) • Basic types can be combined and nested into complex connectors

  8. Semantics of Modelica Connections • Defined by “connect(.,.)” statement • no direction: “connect(a,b)” same as “connect(b,a)” • For causal connectors • Connection means Assignment • Input := output • For acausal connectors • Connection means Kirchhoff’s Laws • Equality for nonflow: • connA.voltage = connB.voltage; connB.voltage = connC.voltage • Conservation for flow: • connA.current + connB.current + connC.current = 0;

  9. Comments • Only “connectors” can be connected • A connector is a specialized class • The designation of connector is thus part of the definition, not of the property (usage) • In Modelica, there is no direct equivalent to SysML constraint parameters • Although acausal (binding) connections exist in Modelica, they can only be used together with a corresponding flow variable to express energy flow • Modelica also differentiates based on “variability” • Constant: never changes (can be compiled in) • Parameter: value can be changed after compilation but is constant during simulation • Variable: value can change during simulation

  10. Compared with ACT • ACT object nodes: • (buffered) in/outputs of tokens • tokens could be continuously streaming to reflect energy flow • Directed token-flow is not a good match Modelica semantics

  11. Compared with IBD • Similar: • Flow ports are similar to Modelica Connectors – could indicate the flow of signals and/or energy • Different: • in/out/inout refers to direction of flow (sign of flow variable), not causality • in/out/inout are defined for port properties (usage) while in Modelica input/output/flow is defined in the connector definition (not usage) • Connections are typed and directed in SysML while untyped and undirected in Modelica

  12. Compared with PAR • Similar: • Parameters are similar to Modelica Connectors • (Binding) connections are untyped and undirected as in Modelica • Different: • Currently only acausal parameters in SysML — an issue is pending to add input/output causality • A Modelica connector is a Class not a property • No notion of flow in SysML — no notion of Kirchhoff’s current law in the corresponding connections

  13. Mock-ups • Modelica  IBD (Chris, Peter, Wladimir) • Modelica  PAR (Chris) • Modelica  IBD+PAR (Sandy)

  14. Case 1: Modelica  IBD EquivalentModelicaModel • Note: • Equations are captured as constraints in the «ModelicaModel» blocks

  15. Case 2: Modelica  PAR EquivalentModelicaModel • Note: • Not all constraint parameters are shown

  16. Case 3: Modelica  IBD+PAR

  17. Spring Mass System - IBD

  18. Analysis Context for Spring Mass System - BDD

  19. Spring Mass System - Parametrics Same structure as ibd, but added constraints and represented flange properties Much of this model would be abstracted away with SysML4Modelica stereotypes for constraining across and through variables

  20. Discussion • No perfect match -- • Simplicity versus explicitness in semantics • What are the reusable models?  to support reuse, we should create SysML structures that match the reusable model structures

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