What bugs me is that even though Baker states in the comment that he proved a particular deficiency in the relational algebra(the expression of transitive closu

What bugs me is that even though Baker states in the comment that he proved a particular deficiency in the relational algebra(the expression of transitive closures), the assertions he uses to lead into this seem extremely vague: they(relational databases) made trivial problems obviously trivial, but did nothing to solve the really hard data processing problems... organizations, budgets, products, etc., are hierarchical; hierarchies require transitive closures for their "explosions"... He never describes concretely what an "explosion" is in a real situation - not in the comment, at least. I'll give the benefit of the doubt that perhaps he brings it up in some paper. But my understanding is that the relational algebra is useful primarily because of its linguistic properties - instead of every problem needing a customized data model and customized graph-traversal solution, it describes how to use a generic query syntax and joins everywhere. While this limits the theoretical power of the system and introduces order-of-magnitude slowdowns, it still solves a major subset of business problems, and it does it with a more compact description than the equivalent graph solution. And that, in turn, means that the theoretical limitations aren't necessarily going to matter for shipping and maintaining a solution, especially when working with a short-term view and small scale. Essentially, he banks on his credentials to turn an "academic" oriented statement into a "industry" one. But from the 70s onward he was writing papers on garbage collection, concurrency and PL theory, not going out and building systems in the industry. So my view is that he's being overly biased towards theoretical purity above practicality, a tendency that has led many an academic astray. (This is not a slam to academics and their pursuit of purity, though. It's a great way to advance the computing arts, and complements well the messy practicality of hackers.)