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Something else that occured to me while reading the responses here: where do you stop moving down the abstraction levels?
The old PostgreSQL HOWTO on tldp.org started with an introductory physics lesson (and a bad one at that). (This HOWTO has since been removed, thankfully). The author's justification was that relational databases work on computers, and computers are based in a physical world, so you can't understand PostgreSQL until you understand physics.
Now there's a reason for a LART if I ever saw one.
Why stop at explaining electrons and atoms, as the author had? Those are based on more fundamental particles. And those are based on yet more fundamental particles. And so on, down the abstraction chain, until you hit truely fundamental particles (if there are any, that is). So in our quest for fully understanding PostgreSQL, we may find ourselves traversing an abstraction chain of infinate depth.
Making the assumption that I am not immortal (though I'll be quite happy if I turn out to be wrong here), I'll just install PostgreSQL and find some documentation elsewhere. If I ever want to dig further, I could learn about B-trees and how relational databases optimize their data layout for spinning magnetic media (like hard drives) and such. I would not jump down to electrons and work my way back up.
Update: Found an old copy of the HOWTO: http://www.yolinux.com/HOWTO/PostgreSQL-HOWTO.html.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.