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Re: how to build a database from scratch

From: Murdoc <murdoc_0_at_hotmail.com>
Date: Sun, 3 Dec 2006 01:26:21 +0000 (UTC)
Message-ID: <xn0euizaa3oe8mx000@news-south.connect.com.au>


Neo wrote:

> > Most relational database systems are based upon Bayer trees.
>
> Is this true? If so why doesn't the relational data model mention trees?

It doesn't need to. B-Trees are not a part of the relational data model, but are almost always used as the internal implementation with the RDMS itself. Index storage is the perfect example. If you have a multiple-component index, e.g. field_01, field_02, etc. then each field would be stored in a separate layer of the B-Tree.

The top layer would contain a separate 'node' for each unique value for field_01 that exists. The second layer would contain, for every unique value of field_01, the corresponding unique values for field_01. That is, there could exist two entries in the second layer for the value "ABC", but they would be related to different values of field_01.

-- 
Received on Sat Dec 02 2006 - 19:26:21 CST

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