SYSML2 — Parsing KerML Feature elements from SysML textual notation

In some cases, parsing certain short-hand SysML notations results in the creation of KerML Feature elements. In particular, according to 8.2.2.13.1 Connection Definition and Usage, shorthand connection notation such as

connection connect x to y;

is parsed into a ConnectionUsage with two end features that are KerML Features. However, it is not possible to create ends that are KerML Features in "long hand" SysML notations. For example, in the notation

connection {
    end references x;
    end references y;
}

the two ends are parsed as SysML ReferenceUsages, not KerML Features.

This means that these two examples, while semantically equivalent, are not actually just different surface notations for the same underlying abstract syntax representation. it would be better to have the shorthand notations parse to fully SysML abstract syntax, as much as possible, so that the shorthand notation is just a different surface representation of a certain abstract syntax pattern that can also be equally represented in the full notation.

Update SysML textual notation productions

The key productions in the SysML textual notation BNF that create KerML Features are:
8.2.2.9.3 Occurrence Successions

SourceEnd : Feature

8.2.2.13.1 Connection Definition and Usage

ConnectorEnd : Feature

8.2.2.17.3 TransitionUsages

EmptyFeature : Feature

These can be changed to produce ReferenceUsages instead.

There are also some other productions that are declared to operate on Features, but which act within other productions that actually create Usages. It does not technically make a difference in this case that the productions are declared to operate on the more general Feature, but it would be somewhat clearer to declare them as restricted to Usages. (Note, however, that ValuePart, PayloadFeature, PayloadFeatureSpecializationPart and various other productions related to FeatureSpecializations must be able to operate on KerML Features, because they are used in the parsing of FlowPayloadFeature, which has to produce a KerML ItemFeature.)

Finally, the expression and feature chain notations are directly adopted into SysML from KerML and so parse entirely to KerML abstract syntax elements. However, there is not really any practical "long hand" notations for these constructs in SysML, so the current parsing is not a problem.