This is interesting, but I admit I am a bit confused.<p>Having read &quot;An Introduction to Database Systems&quot; by C.J. Date (<a href="http:&#x2F;&#x2F;www.amazon.com&#x2F;Introduction-Database-Systems-8th&#x2F;dp&#x2F;0321197844" rel="nofollow">http:&#x2F;&#x2F;www.amazon.com&#x2F;Introduction-Database-Systems-8th&#x2F;dp&#x2F;0...</a>), I have a tremendous appreciation for Relational Algebra and Theory which allows for the closed functional nature&#x2F;syntax of SQL which holds true across the various normal forms (1st-5th).<p>Perhaps due to my own lack of understanding, I always assumed that without an underlaying relational model SQL loses its closure.  So for me, I always thought the distinction between SQL and NoSQL was whether or not the underlying database model was relational.<p>Sure for many of the queries against a non-relational model you could adopt a SQL-like syntax (which many languages seek to do), but it would no longer be operating in the closed Relational Algebra space.<p>Could you comment on this and help me understand the finer points&#x2F;where I went wrong?