| Logical Structure [message #536525] |
Wed, 21 December 2011 05:33  |
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kamran0931
Messages: 17
Registered: December 2011
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Junior Member |
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Hi
Why we need logical structures, i mean why this distribution ?
Tablespaces
Segments
Extents
Data Blocks
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| Re: Logical Structure [message #536736 is a reply to message #536727] |
Thu, 22 December 2011 07:06  |
cookiemonster
Messages: 13920
Registered: September 2008
Location: Rainy Manchester
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Senior Member |
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And what sort of answer are you expecting other than "Because oracle designed it so?"?
Seriously, we don't know the thought process behind that decision, oracle haven't published it as far as I'm aware. I expect most actual oracle employees don't know either.
Why does it matter?
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| Re: Logical Structure [message #536753 is a reply to message #536525] |
Thu, 22 December 2011 08:19 |
John Watson
Messages: 8929
Registered: January 2010
Location: Global Village
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Senior Member |
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I'll have a go at this.
In 1970, Ted Codd invented the ralational database, in this paper
http://www.seas.upenn.edu/~zives/03f/cis550/codd.pdf
Since then, many companies have written implementations of this model. One of these companies is Oracle. All the implementations are different, but they all get to the same place (if they didn't, they wouldn't be relational databases.)
If you read that paper and some of the many followups (Google for "Codd's 12 rules" and take it from there) it should become clear. The way I think of it is that there must be an abstraction of the logical structures that the programmers see from the physical structures that the system administrators see.
This is your introduction to relational database theory. Enjoy.
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