I made https://github.com/mamcx/tree-flat as flattened stored tree in pre-order that allows for very fast iterations even for childs/parent queries. Is based on APL, so not that novel.
I also like a lot the relational model, is not that much represented so I making a language on top of it: https://tablam.org.
Nice! I'm curious to see where you take TablaM. I agree that the relational model is not nearly as well represented as a basis for programming language semantics as one might hope.
I also like a lot the relational model, is not that much represented so I making a language on top of it: https://tablam.org.