Thank you for your reply,
there is another issue.
In my child-object I have an attribute number_1 and I display the sum of all these attributes in my parent object.
Is it possible, to display the sum of all child-number_1-attributes in my child-object?
How do I design my rule for the sum?
child.sum_numbers = SUM child.number_1 WHERE child.parent = ????
Regards,
Christian