SYSML11 — SysML needs instance specs

SysML needs instance specs capabilities for several reasons

1) compatibility with UML and many users' expectations
2) ability to do animation
3) ability to show particular values at a time
4) educational value / illustration value

No need for a new diagram type, instances can appear on block and sequence diagrams.

No practical substitute has been found for the use of instance specifications to
specify examples, test cases, and other occurrences of blocks defined in SysML
user models. Because SysML tool implementations are based on UML
implementations, diagram support for instance specifications can be simply a
matter of relaxing any constraints that would disable access to these elements
from within a strict SysML subset. Instance specifications are already included in
the SysML metamodel to support other elements of SysML such as the Unit
stereotype and the initial values compartment.
Because SysML already defines a taxonomy of its standard diagram types
(summarized in Annex A and defined in the specification chapters), use of
instance specifications in SysML must be identify a diagram context where they
could appear. While they might appear in more than one diagram context, the
simplest approach for uniformity in user models is to rely on a single context
where they could be shown. Instead of defining an entirely new diagram context,
the block definition diagram is a natural place to show either the definitions of
blocks or instances specifications of these blocks, or any mixture of both. Since all the required metamodel elements for instance specifications are already
present in SysML, the inclusion of their existing UML-based notation can be
specified merely by including their diagram elements in the table of graphical
elements which can be shown on block definition diagrams