Formal Underpinning

A formal foundation can be helpful in many ways, one of them query plan optimization.

Relational databases are said to have a clear formal foundation and most people would point to papers about relational algebra. Unfortunately, SQL - driven by industry needs - has long left this boat having introduced object-orientation (still to a limited degree, which keeps an impedance mismatch with OO programming), functions, triggers and much more other fluff. I am not aware of a standardized formal model which covers this all.

In fact, this is something which has been worked on for a while for TMQL and my expectation is that the TMQL semantics is - via several steps - not only defined in prose, but also formally based on abstract algebra. As user you may not care, as engine developer, you might appreciate it.