SYSML21 — Graphical notation incomplete to model RequirementDerivation and CauseAndEffect constructs

The standard libraries RequirementDerivation and CauseAndEffect both declare a connection definition or connection usage to model:

1. requirement derivation from an original requirement to one or more derived requirements.
2. causation and multicausation from one (or more) cause to one (or more) effect.

User-defined keywords #original, #derive, #cause, #effect are used to effectively declare the roles of the various ends of the relevant connection definitions or usages.

Since typically the ends of the connection definitions or usages do not have names, the Graphical BNF (in particular production rolename in 8.2.3.13) currently does not provide a suitable notation to distinguish between original and derive requirements nor between cause and effect occurrences.

A possibility is to allow user-defined keywords #original, #derive, #cause, #effect to be used as rolename in connection definition or connections usage notation, possibly enclosed by guillemets.