Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?

"Bob Badour" <bbadour_at_golden.net> wrote in message news:KZh4a.9$k32.1286180_at_mantis.golden.net...
> "Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message
> news:ckb4a.14$7H6.123_at_news.oracle.com...
> I disagree. What it says actually depends on the full predicate--internal
> and external--and not on whether Item represents a set or a multiset. To
my
> anglophone human eyes, it looks like it says Milk is an Item.

My typo, again. In multiset model we have

Item

whereas, in set model

Item Count
---- -----
Milk 2
Soda 1

Now, the first entry in the multiset model tells that there is at least one Milk container, while the first entry in the set model tells us that there are exactly 2 containers. The set model has more precision, here, granted.

> Are you saying that a set-based relational dbms with full support for
> domains would not allow the user to freely transform data among
> representations?

Please, write down a query that transforms

Num

---
2
5

into

Seq# Num
---- ---
1    2
2    2
1    5
2    5
3    5
4    5
5    5

in pure relational syntax. Now, the same, please, without explode/recursion
operator.



> The distinction [between physical and logical] is an important one.


> You do yourself a disservice by losing sight of it.



There are limitations of every model. The question always is if the goals
that one wishes to achieve warrant changing the model.