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Re: Mazes, trees, and forests

From: x <x-false_at_yahoo.com>
Date: Mon, 26 Apr 2004 14:23:44 +0300
Message-ID: <408cf090$1@post.usenet.com>

"mAsterdam" <mAsterdam_at_vrijdag.org> wrote in message news:4089a993$0$563$e4fe514c_at_news.xs4all.nl...
> x wrote:
>
> > Why do you consider only the foreign-keys of R1 ?
>
> Following the forestify algorithm eventually all foreign
> keys will get their turn.

Sorry. Why only the FOREIGN-KEYS and not ANY subset of attributes ?

> > A user can connect any two relations on any two attributes of compatible
> > types.
> Sure, and by expanding along those lines every user can
> build his own forest.

So there would be a forest for every user ?

> > Do you consider only the base relations or any relation ? ;-)
>
> Well, I did. With 'any relation': you mean every conceivable relation
> on a base?

"any relation" = base or derived relation

> > How can someone (other than the user) predict for what pairs of
attributes
> > the join of two relations make sense ?
>
> Why would anyone *want* to predict that? Sensible types help, but beyond
> that ... could you clarify how this impacts the suspicions I mentioned
> in the first posts?

Well, you said:
"This TELLS us something about wether and how much of the data in the database can be expressed as trees and THE LOSS we incur by doing so."

What do you mean by the "data expressed as trees" ? Why there would be any loss in the "data expressed as trees" ? Do you consider "the data in the database" is "the stored data" ? I'm also considering that some "derived data" may be lost. In my opinion, in a RDBMS the data is in the:

-  names of the named relations
-  names of the attributes
-  values of the attributes of any relation (base or derived)
-  integrity constraints
-  formula that define a derived relation
-  associations of the above

> > This is why a relational DBMS is different from other types of DBMSs.
>
> Do you mean to imply that with 'other types of DBMS' (historic I assume)
> can't connect as they please? I must be misreading you.

By "other type of DBMSs" I'm referring to "hierarchical" or "network" DBMSs.
Maybe they can connect as they please. But with what cost ? I was taught that one need to write long routines to achieve some "connections".

Restricting the connections only to (PK,FK) keys of base relations sound like restricting the connections only to the existing physical access paths.

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Received on Mon Apr 26 2004 - 06:23:44 CDT

Original text of this message

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