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

In message <t6adncXPEMhfsVfdRVn-sw_at_comcast.com>, Laconic2 <laconic2_at_comcast.net> writes
>> It's a slippery handle, but maybe - but be careful asking about "the same
>> as" in an OO context - that subject gets very confusing to OOers. :-)
>>
>> A related and interesting issue is that of relation-valued attributes as
>> primary keys; for example, from one of Date's non-free papers, a relation
>> with a single column: a relation of siblings. Since in a relation order is
>> irrelevant, you couldn't insert the tuple ( {Eric, Curt, Amy} ) if the
>> relation already contained ( {Amy, Curt, Eric} ), for example. He did a
>> similar thing with prime factors; the relation consisted of 2 columns:
>> Integer and {Integer}.
>>
>> Anyway, I'm rambling...
>
>I don't think it's rambling at all... It's precisely where I was heading
>with the question.
>
>There's a second question, along the same lines.
>
>In the recent Pick example, showing an invoice, there's a list of account
>numbers, and a correlated list of amounts.
>That is, the second amount "goes with" the second account number. But, in
>the earlier pizza pick example we had a list
>of three toppings and an uncorrelated list of three cheeses. Now my
>question is this: how the heck do you know that in one case the two lists
>are correlated and in the other example they are uncorrelated?
>
>Are you "just expected to know" the logical structure of invoices and
>pizzas enough to draw this inference?

No. Pick stores metadata in its dictionaries, and has a concept called ASSOCiation.

With the pizza, there is no ASSOCiation defined between CHEESE and TOPPING, but with the invoice there is an ASSOCiation between ACCOUNT.NO and AMOUNT. That is, if the programmer has remembered to define it ...

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