When adding a relation to an embedded document, add a warning that the embedded documents can only be used for embedded relationships and offer to change it to a concrete document (provided it’s not used as relation by an other class.

When adding an embedded relation to a non-embedded document, add a warning that the embedded documents can only be used for relationships and offer to change it to an embedded document (provided it’s not used as embed by an other class)

Using a document class both embedded and non-embedded is not recommended.

This require an option to make document class "EmbeddedDocument"

When creating a relation to itself, if this is a new class it can’t be selected. Solution : add the class that is currently being created to the list.

Or allow creating new classes directly when creating a relation ? With some nesting…