[metaphorm]

> defining foreign keys is like setting a pointer to a parent instance.

I can't agree with that statement, though I'm sympathetic to why you would say it. A foreign key is something that essentially doesn't translate from the world of Tables/Rows to the world of Classes/Objects.

In the relational data model the foreign key is a convenient place to include an index for joining on. What does join even mean between two classes? The closest you'll typically get is nested objects, but that's not quite right. A row produced from table joins isn't a nested data structure. It's still flat. The join operation in relational algebra has no direct equivalent in OOP.