All Cities have a Country [one to one relationship]
Cities can have the same name in a different Country.
Country can have many Cities [one to many relationship] (maybe Country means Destination?)
Journey has 2 Cities - each having a Country - Start City and End City
Is Country the Destination Country? Which may or may not have a City in Journey?
These links may be useful [especially the first four or five]
@David : thanks for the links but I know how to design a basic DB, here it's just a problem of finding a way to get the results I need displayed with FM (with my model it would be easy to get what I need in SQL)
@Phil : I have tried 2 table occurences but then there is still a problem as you then have a good starting point to work with a "CITY" based layout, but not a COUNTRY based layout... cf the goal : "how do I get a list of COUNTRIES for which NO CITY is involved in any travel"
or maybe I've missed something
Any other tip / idea ?
My point is that your current relationships won't work and are incorrect. A record in Travels only matches to a record in cities if the id values in BOTH the from and to fields match the ID field value in Travels. I don't see how that relationship will work at all for you.
Once you have valid relationships here, you can use the count function in a calculation field in cities to count the number of related Travels|From and Travels|To records. A search for Countries where this field is blank or 0 will provide your list of countries that do not have any related travel records.
Count ( Travels|From::IDFrom_City) + Count ( Travels|To::IDTo_City )