I've updated the article to use data that does not (generally) change from year to year: country and area instead of city and population. This should eliminate the semantic issue and make it clearer.
Probably okay for your tutorial...but country areas change from time to time due to territorial disputes being resolved, or due to older erroneous info being changed.
Cities can also change country. Pristina used to be in Serbia but is now in Kosovo (although this is not universally acknowledged). Bratislava used to be in Czechoslovakia but is now in Slovakia.
While just pedantic in this case, it demonstrates how hard it can be to create a strong data model.
Comments
I've updated the article to use data that does not (generally) change from year to year: country and area instead of city and population. This should eliminate the semantic issue and make it clearer.
Probably okay for your tutorial...but country areas change from time to time due to territorial disputes being resolved, or due to older erroneous info being changed.
Cities can also change country. Pristina used to be in Serbia but is now in Kosovo (although this is not universally acknowledged). Bratislava used to be in Czechoslovakia but is now in Slovakia.
While just pedantic in this case, it demonstrates how hard it can be to create a strong data model.
Yes, that's quite true. Creating even what I would have thought to be a 'simple' example isn't as trivial as I have expected.