Subrelation Schema (targeting UsedInDiagramAsXXX classes) could allows disconnected edges (if property cardinality is 0:1) or forbids it (if property cardinality is 1:1).
Ability to draw new disconnected edge
- disconnected from one node
- disconnected from all nodes
Ability to edit connected edge and make in disconnected:
- Disconnect connected edge from one node
- Disconnect connected edge from all nodes