Un Relational

UnRelational is something that isn't relational - for example deeply nested trees and hierarchies, or objects in OOP.

Yet there are ways sometimes to map UnRelational data to Relational databases (XmlRelationalMapper, ObjectRelationalMapper)

Just about any data structure or language can be represented in relational form. I cannot find any "hard" distinction. I can only find "bad" or "difficult to use" relational.

See also RelationalModel, RelationalLoopHole