Key field should not be mandatory

Hi experts,

I want to extend model BP with a new entity type for an industry specific table. The table has several key fields so I created corresponding type 3 entity types for them and linked them to the main entity type with Qualifying relations.

For Qualifying relations only a cardinality 1:N can be set. But this makes the fields mandatory. For one of the key fields this behaviour is not wanted as mostly no value is entered.

Is there a way to model key fields without such a side effect?

Best regards,

Markus