The ActivityEdge, Transition, and Connector metaclasses do not extend (directly or indirectly) the Relationship metaclass (although the notations for them do indicate a kind of "relationship").
UML2 simplified key "relationship" metaclasses hierachy - ADVANCED REFERENCE ONLY This content has been marked as discussing an ADVANCED topic! Gallery Tutorial TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo Section 01:02: UML 101 for model-based systems engineering with SysML Slide kind UML Profile Diagram
It captures the definition of blocks in terms of properties and operations, and relationships such as a system hierarchy or a system classification tree Source OMG Systems Modeling Language (SysML) 1.6
The Block Definition Diagram in SysML defines features of blocks and relationships between blocks such as associations, generalizations, and dependencies. Source OMG Systems Modeling Language (SysML) 1.6
Magicdraw/Cameo has a powerful "implied relation" facility for use in query tables, dependency matrices, and as element properties