Well, the best analogue to the Codd's relational algebra is Hewitt's actor model in my professional opinion. Both are based on mathematical formalism, though the Actor Model goes a bit further in that it's also informed by physics.

But, just as SQL doesn't really implement Codd's relational algebra, so it is the case that most so-called OOP languages miss the mark vis-à-vis Alan Kay's original conception.

The analogy is buttressed by the fact that many early RDBMSs didn't even support joins (path independence being an essential characteristic of RA), just as many mainstream OOP languages didn't/don't idiomatically endow objects with a strong way to protect themselves (encapsulation being a necessary characteristic, thus pervasive use of setters being the main sin)). But, Kay did praise Erlang for getting OOP right.