[dragonwriter]

> The article as I read it is trying to make a broader point, that there are underlying mathematical principles that inspired Codd’s relational model.

The relational model is a direct product of a set of mathematical principles Codd put together called relational algebra, which deals with sets of tuples called relations.

Nothing in the article addresses any of the mathematical underpinnings of the relational model. Its blowing smoke at an audience that it expects to know next to nothing about the topic.

> One goal of the article seems to be to inspire a curiosity in knowledgeable readers: what happens if you build a document database that also supports the same mathematical principles that inspired the relational model

The features of RDBMSs that they seem to be suggesting FQL supports are ACID transactions. While that's an important feature of RDBMSs, it isn’t the same thing as the mathematical principles addresses by the relational model, whether relational algebra or the more general set theory that inspires it. The article isn't directed at knowledgable readers.