Re: In an RDBMS, what does "Data" mean?

From: Anthony W. Youngman <wol_at_thewolery.demon.co.uk>
Date: Fri, 18 Jun 2004 17:51:50 +0100
Message-ID: <1aPaN6Am2x0AFwN3_at_thewolery.demon.co.uk>


In message <T_GdnUOFSYwWD1TdRVn-vA_at_comcast.com>, Laconic2 <laconic2_at_comcast.net> writes
>> He did say that, and I've been thinking about it, and am not sure it's
>> accurate. The order of values in a list attribute in a Pick file seems
>> primarily to correlate with other attributes that relate to the same
>> "nested" entity - e.g. a line item. Those can easily be spit out in
>> correlated lists by foreign key traversal. Other ordering would have to be
>> imposed, and maybe that's where the discrepancy is. Relational requires
>that
>> if order is important, you make it an attribute. I've never found such to
>be
>> a problem - in most cases, orderings are pseudo-IDs.
>
>Months ago, I asked whether a pizza with pepperoni and onion was the same
>as a pizza with onion and pepperoni.
>
>I got several cute responses, but nobody really addressed the underlying
>issue. Sounds like you've got a handle on it.

In other words, is it a set, a bag, or a list?

Note that it's easy to go from a list to either of the other two. But in order to go back, the set or bag needs to contain extra data (ie the order) over the list.

Because Pick stores attributes as lists (if relevant) the order is available to the db engine as metadata if required. And it can't be accidentally lost by an analyst :-) So I would argue that storing things as lists is better, because you can always get the other two if you want.

After all, your question could be taken to mean "Is it a pizza with both pepperoni and onion" or "is it a pizza with pepperoni on it then onion on top of that".

If the analyst hasn't taken it into account, then relational is sunk without a redesign. With Pick you just tell your till-operatives that it's to be entered as an ordered list, not a set :-)

Cheers,
Wol

-- 
Anthony W. Youngman - wol at thewolery dot demon dot co dot uk
HEX wondered how much he should tell the Wizards. He felt it would not be a
good idea to burden them with too much input. Hex always thought of his reports
as Lies-to-People.
The Science of Discworld : (c) Terry Pratchett 1999
Received on Fri Jun 18 2004 - 18:51:50 CEST

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