I think what the parent meant is that such a tree is fundamentally relational (not merely that it can be modeled as such). Since a relation is just a mapping be

I think what the parent meant is that such a tree is fundamentally relational (not merely that it can be modeled as such). Since a relation is just a mapping between tuples and a set of logical values (TRUE and FALSE in most cases) then clearly there is a well-defined relation among the notion of 'parent' and 'child'. Thus the problem is the de-facto standard query language. It seems to me that we could use new special query language (or an extension to SQL) that could handle creating trees from pure relations in a performant and lexically elegant way. Or maybe it’s already been tried and I missed it. (edit: looks like a lot of smart people have already figured it out)