I am not sure how to implement this, so if anyone has any ideas i will be glad to hear them. The problem is that I have the tables country, region and submission. the table submission uses the country and region parts as a reference selector. When a submission is created i want to make it that when the user chooses a region e.g. EU, only a list of countries in the EU will appear in another reference selector.
Assuming I understand what you want to do and have properly provided a relation between Country and Region (ie, a reference from Country to Region), you can achieve this by using 'Constrained by' functionality or an Xpath constraint: