Re: In an RDBMS, what does "Data" mean?
Date: Tue, 15 Jun 2004 16:28:16 +0300
Message-ID: <40cef875$1_at_post.usenet.com>
"Laconic2" <laconic2_at_comcast.net> wrote in message
news:TPSdnXgqT7AJcFPdRVn-jA_at_comcast.com...
>
> "Tony" <andrewst_at_onetel.net.uk> wrote in message
> news:c0e3f26e.0406150138.d389afd_at_posting.google.com...
> > "Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message
> news:<qZztNxCLLizAFwnY_at_thewolery.demon.co.uk>...
>
> > False. A relational database contains a lot of metatdata:
> > primary/unique keys, foreign keys, other constraints. All of these
> > are available to the RDBMS for optimisation purposes. To take your
> > invoice example, the RDBMS "knows" that a given invoice has 14 invoice
> > lines just as surely as Pick does.
>
> Excellent, excellent point. So many people fail to recognize this feature
> of an RDBMS.
And all this "knowledge" about data won't spare you from writing code for assembling several SQL statements.
What Anthony said is this:
1) we entered all data in an invoice *at once* in the database
2) we should be able to work on the *whole* as well as on a part of this
data by means of the DBMS
3) we should be able to ask for the *same* data we entered in the database
as a whole by means of the DBMS.
If we are not able to do this with a RDBMS, then something is missing.
He call this metadata.
> When I built a "data mart" in Oracle as a star schema, I included all the
> primary and foreign key constraints, even though it slowed down loading.
> The advantage came when I went to copy the star into Cognos (Impromptu or
> Power Play, I forget)
> Both Cognos and the Oracle optimizer recognized my star schema for what it
> was, and made appropriate use of that fact.
You were lucky.
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