The Systems Modeling Language (SysML) is a particularly successful offshoot of the Unified Modeling Language (UML) tailored for Model-Based Systems Engineering. After a decade of growing use of SysML, in 2017 the Object Management Group (OMG) issued a Request for Proposals (RFP) for a new version of the language. A year into the ongoing work to respond to this RFP, it is clear that SysML v2 needs to be more than just an expansion of the functional capabilities of SysML. Rather, it must address fundamental architectural issues that have made it difficult to further evolve SysML v1 to address the needs of its user community. Therefore, the language is being re-designed using a new kernel metamodel with formally grounded semantics. This kernel can then be extended using semantic model libraries, rather than by expanding the language metamodel itself. This approach will allow SysML v2 to be not only the modeling language for traditional systems engineering, but also the foundation for a whole new generation of modeling languages.

1. SST
Vienna University of Technology
18 February 2019
Ed Seidewitz
Chief Technology Officer
Model Driven Solutions
SysML v2 and the
Next Generation of Modeling Languages

2. SSTWhat is SysML?
 The Systems Modeling Language™ (SysML®) is a
profile of UML that
“…supports the specification, analysis, design, and verification
and validation of complex systems that may include hardware,
software, information, processes, personnel, and facilities” *
 SysML has facilitated awareness and adoption of
Model-Based Systems Engineering (MBSE).
 SysML has evolved to address user and vendor
needs.
 v1.0, adopted in 2006; v1.5, current version; v1.6, pending
approval; v1.7, in process
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* From OMG Systems Modeling Language specification, v1.5, Introduction

3. SSTSysML v1 Language Architecture
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From OMG Systems Modeling Language specification, v1.5, Figure 4.2

4. SSTSysML Block Definition Diagram
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SysML Block Definition
Diagram (IBD) is an
adaptation of the UML
class diagram.

5. SSTSysML Internal Block Diagram
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For example, can
nested parts have
different properties?
No, internal structure
is the same for all
instances of a type.
SysML language design has been limited by being a UML profile
SysML Internal Block
Diagram (IBD) is an
adaptation of the UML
composite structure diagram.

6. SSTOther Desired Enhancements
 Functional enhancements
 Improved integration with analysis, variant modeling,
geometric modeling, etc.
 Flexible visualization
 Textual, diagrammatic, tabular, dynamic, interactive, etc.
 Improved interoperability
 Between SysML tools and with other tools
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7. SSTSysML v2 Requests for Proposals
 SysML v2 RFP issued December, 2017
 Initial Submission: November, 2019
 Revised (Final) Submission: November, 2020
 SysML v2 API & Services RFP issued June, 2018
 Initial Submission: February, 2020
 Revised (Final) Submission: February, 2021
 SysML Submission Team (SST) formed December
2017
 Leads: Sandy Friedenthal, Ed Seidewitz
18 February 2019

8. SSTSysML v2 SubmissionTeam (SST)
 A broad team of end users, vendors, academics, and
government liaisons
 Currently 90+ members from 60+ organizations
 Developing submissions to both RFPs
 Driven by RFP requirements and user needs
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9. SSTUsage Focused Modeling
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A paradigm shift to make SysML v2
more precise and intuitive to use
 Emphasizes modeling of usages (e.g., parts on an
IBD)
 Decompose, connect, and group usages
 Supports other language requirements
 variant design configurations, individuals, analysis,
verification, …

10. SSTVehicle: Internal Block Diagram (SysML
v1)
18 February 2019
Internal structure is
the same for all
instances of a type.

11. SSTVehicle: Internal Block Diagram (SysML
v2)
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Connector to
nested port
Usage-specific
property values

12. SSTSysML v2 Language Architecture
18 February 2019
SysML v2 will be based
on a kernel metamodel,
rather than UML.
The kernel semantics
will be grounded in a
declarative formalism.
Full language semantics
will be specified using a
semantic model library.

13. SSTKernel Abstract Syntax
2018-12 Baseline
18 February 2019
Principles
• No abstract classes
• Library-based semantics
• Reification of meta-associations
as relationships
Highlights
• Flexible packaging
(including ”smart” packages)
• Features as “categories”
(allowing nested features and
features as types)
• Deeply nested connector ends
• Common model for behavior
• Expressions as features typed
by functions
Note: Relationships are
notionally association classes,
but cannot really be
represented as such in MOF.
• Builds on previous work done toward a Kernel Modeling Language (KerML).
• Uses generic, not SysML-specific, terminology (e.g., “class”, not “block”)

14. SSTKernel Abstract Syntax
Relationships
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Reified
membership
model Unified
connector/flow
model
Integrated
generalization
model

15. SSTKernel Model Library
Base and ScalarValues
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16. SSTClasses
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LibrarymodelSystemmodelSystem
The stereotype
indicates the intended
kernel metaclass for
the model element.
“Individuals” here are not
model elements, but
members of the semantic
extent of a class.
A class with no superclass
automatically specializes
the library class Object.

17. SSTFeatures
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LibrarymodelSystemmodelSystem
The instances of a feature are
ordered pairs of individuals.
A feature typed by an object
class automatically subsets
the library feature objects.

18. SSTNested Features
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LibrarymodelSystemmodelSystem
An instance of a nested
feature is a pair in which the
first member is also a pair.

19. SSTExpressions
Mapping to Abstract Syntax
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class Assembly {
feature m = c1.m + c2.m;
part c1: Component1 {
feature m: MassValue redefines Quantity;
}
part c2: Component2 {
feature m: MassValue redefines Quantity;
}
}
The user model with a surface expression
language has this composite structure.

20. SSTExpressions
Usage of Model Library
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21. SSTThe Next Generation
 The SysML v2 specification will include a separate
volume with a self-contained definition of the Kernel.
 The system-specific extensions will be largely built
using model libraries, written in SysML v2 itself.
 It will be natural to build a other modeling languages
on this rigorous foundation.
Will UML v3 be a profile of SysML v2?
18 February 2019