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This is interesting, but I admit I am a bit confused.

Having read "An Introduction to Database Systems" by C.J. Date (http://www.amazon.com/Introduction-Database-Systems-8th/dp/0...), I have a tremendous appreciation for Relational Algebra and Theory which allows for the closed functional nature/syntax of SQL which holds true across the various normal forms (1st-5th).

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.

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.

Could you comment on this and help me understand the finer points/where I went wrong?

Syntax and being relational are orthogonal.

You can set up non-relational data structures in SQL. You can set up a relational data structure in virtually any programming language.

However what the NoSQL people are learning is that smart developers really want relational models. So they are offering the features that can be used to achieve that.

That's where I think where most NoSQL proponents start to miss the value of relational models and the closed Relational Algebra it allows.

As I understood it, SQL was a language for describing the Relational Algebra which was a closed mathematical concept.

You can take the syntax, assign functions to produce output from a non-relational model, but it's no longer SQL...and it's underlying power (the closed Relational Algebra) is no longer present.

So in a sense syntax and being relational are orthogonal, but syntax isn't the defining characteristic of SQL (or why it's so powerful). I think a more insightful statement is: SQL (Relational Algebra) and being relational are codependent and relational and non-relational are orthogonal.

Which, if I am not mistaken (and again I am still trying to understand the finer points which is what motivated my original comment), NoSQL people fundamentally _cannot_ offer a query language similar to SQL based on the closed relational algebra.

They can mimic the syntax to make it more intuitive for new users coming from traditional RDMBS environments, but it's fundamentally _not_ SQL/relational algebra.

But again, I am just a cursory admirer/learner and I am still trying to iron out my own understanding of the underlying theory. So all additional information/clarifications welcome :)

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