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

In message <n61Ac.54$NZ6.29_at_newssvr33.news.prodigy.com>, Eric Kaun <ekaun_at_yahoo.com> writes
>> Plus, if you're going to get the order right,
>> you've had to convert the original metadata (implicit order) into real
>> data and do a sort (both of which I would say is you creating data and
>> then providing it upon extraction - so you haven't actually stored the
>> invoice properly in the database!
>
>You're not creating it (it was there implicitly already), but you are making
>it explicit. Is that bad? I don't think so, but it's debatable. I would
>again raise the spectre of additional metadata other than order... what else
>"should" be there in a data model? And how best to represent it?

Is that bad? Well, you're converting it from metadata into data, so (a) the db engine no longer knows anything about it and so can't optimise based on it, and (b) you're forcing this knowledge to be stored in the applications. If you want to store "everything" in the database, you're now in a catch-22.

I'd say both of these are bad, but then I would, wouldn't I :-)
>
>> When we put an invoice into a Pick database, the data in the db maps
>> CLEANLY to the data on the paper. And the db has all the metadata it
>> needs to convert this to a relational view should a user so desire.
>
>Except that your query language is less symmetrical as a result of treating
>assertions about line items differently than other predicates. At this point
>I'm just repeating myself though...

Agreed. But you're assuming symmetry is a good thing. Also - you try joining two tables, linked by a one-to-many relationship. You want to list the "one" table, just one instance of each row, but select on an attribute in the "many" table. Your query language is going to be asymetric too - you're going to have an asymetric join, or need the keyword "unique", or something like that. The asymetry is a consequence of the "one to many"-ness, and not of the Pick representation.

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