Firstly, I find it ironic that a post that talks about "Security" as a top 10 concept has so many uncaught spam comments :-) Secondly, and less trivially, I have to say that the phrase "relational databases" does stick out like a sore thumb, not because it's a bad idea, but because it's "product-class" based, rather than "concept" based. I'd agree that learning how to manage complex data structures is a core concept... and I'd agree that learning how to map complex structures onto SQL-based backends is, at time of writing, a good part of that learning... ... but I'm unconvinced that it's in the same league as layering or algorithmic complexity. ... oh, and I feel the same way about cloud computing, by the way, but the difference is that strikes me as the NEXT wave, that might abstract OUT the need to think in SQL-join terms :-) - Mark Harrison from FriendFeed MT Plugin