From: Joshua Gargus what is it that RDBs *fundamentally* get correct?
People find it easy to understand tabular data and to cross-reference between tables. Relational databases contain tabular data. So people find relational databases easy to understand compared to the alternatives. Other than the uniformity ("everything is either a tuple or an atomic value"), there's little else to commend them - but that ease of understanding has been enough, I think.
The rest of the system is optimisation to try to get relatively efficient use of the machine despite expressing the problem in ways that are easy for humans to understand. Oh, and trying to make up for the *dreadful* query language that IBM inflicted on the world with SQL. I learned the principles of relational systems with db++, a very odd relational system that used a very clean relational algebra where select, project and join were first-class operations. It's certainly helped me cut through the fog of SQL, where the principles are far less clear!
- Peter