Comment by 9rx

> Why has no truly relational DBMS has ever been widely available in the marketplace?

Postgres was "truly relational" for a significant portion of its life before finally losing the battle with the SQL virus. There is probably no DMBS more widely available. Granted, it wasn't widely used until the SQL transition.

> SQL isn’t relational.

This is key. Relations are too complicated for the layman, the one who is paying for it, to understand. Tables are more in tune to what is familiar to them. The hardcore math/software nerds might prefer relationality, but they aren't the ones negotiating multi-million dollar contracts with Oracle/IBM.

I remember when Postgres moved to SQL. People started billing it as being Oracle, but free. That got non-technical manager attention. Without that marking success appealing to the layman, I expect nobody would be using it today.