your product seems to be very good, but it seems to lack in supporting 2-way relationships, e.g. if we have a relationship between CARS and PERSON inside a family, a PERSON can drive multiple CARS and a CAR can be driving from multiple PERSONS : we need a relationship with a cardinality 0..N at its two ends.
maybe I have seen it too quickly but I don't have seen it in your program.
is it possible?
These are not supported directly. You would have to draw one relationship between CAR and PERSON, and another between PERSON and CAR.