SYSML11 — Section: 6.1 Levels of Formalism

Add a brief statement to Section 6.1, Levels of Formalism, to clarify that SysML reuses UML instance semantics, adapted as necessary for description of systems. A brief statement of UML instance semantics can be found in the UML Superstructure specification (ptc/06-04-02) under 6.4.2, Semantic Levels and Naming, under the paragraph labeled "Instance level."

Following is the paragraph labed "Instance level," which now appears in the
section numbered 6.3.2 in the UML 2.4 Superstructure Specification:
Instance level – These are the things that models represent at runtime.
They don’t appear in models directly (except very occasionally as detailed
examples), but they are necessary to explain the semantics of what
models mean. These classes do not appear at all in the UML2 metamodel
or in UML models, but they underlie the meaning of models. We provide a
brief runtime metamodel in the Common Behavior chapter, but we do not
formally define the semantics of UML using the runtime metamodel. Such
a formal definition would be a major amount of work.
Since SysML already includes the semantics of existing UML elements, except
as specifically changed or extended by SysML, this existing language (which has
not changed since UML 2.1) applies to SysML.
SysML already includes the following statement in Section 6.1, which leaves
open the option to consider further semantics in the future, but in the meantime
leaves them open just as does UML:
SysML is specified using a combination of UML modeling techniques and
precise natural language to balance rigor andunderstandability. Use of
more formal constraints and semantics may be applied in future versions
to further increase the precision of the language.
Given the generality of both the UML and SysML statements about formal
semantics, no change is required to the current version of the SysML
specification. A new issue could be raised if future versions of UML adopt a
formal specification of semantics that would also need to be adapted or reflected
by SysML, but such an issue should be raised against specific future changes to
UML.
Disposition: Closed, no change