Re: The Practical Benefits of the Relational Model

From: Paul Vernon <paul.vernon_at_ukk.ibmm.comm>
Date: Fri, 18 Oct 2002 11:36:38 +0100
Message-ID: <aooo8t$1h9s$1_at_sp15at20.hursley.ibm.com>


"Lauri Pietarinen" <lauri.pietarinen_at_atbusiness.com> wrote in message news:e9d83568.0210161345.6776840b_at_posting.google.com...
> > Out of interest, how does D4 insert into this view?
> >
> > (A UNION B) MINUS (A INTERSECT B)
> >
> > It seems to me to be entirely arbitrary to insert into A rather than B,
or
> > vis-versa, and only slightly less arbitrary to not allow any inserts at
> > all.
>
> The latest article in www.dbdebunk.com (By Date and McGovern)
> might shed light to that problem.

I struggle to see the insight that the Principle of Orthogonal Design claims to bring. In particular if we assume that relvar names are simply short cuts for the set of attribute names in a relvar, and therefore relvar names are strictly optional, then it should *not be possible* to create two relvars in a database with the same set of attribute names. (BTW I've assumed that: attribute_name -> attribute_data_type).

In other words I say that it *is* the names that have meaning (contrary to what D&D say in TTM). Why appeal to some external meaning that we don't even try to capture in the database - thereby breaking the Information Principle? I'd agree that external predicates read better than a conjunction of attribute names, but they should not actually add any extra 'meaning'.

In the article, Chris & David suggest that they are trying to insert tuples that have no attibute names into the database. This is wrong. What they should be inserting are tuples such as:
  <LOVER: Romeo, LOVEE: Juilet>

then with sensible relvar attribute names, e.g. (LOVER & LOVEE) and (HATER & HATEE), there is not need to talk about external meanings that are not known to the DBMS.

Now it might be a bit of a pain to have a RDBMS that did not allow two tables to have the same attribute names (and types) in the same *database*, but frankly I could live with such a restriction if it enforced the Orthogonal Design Principle (and if any local relvars we not seen as part of the main database)

Regards
Paul Vernon
Business Intelligence, IBM Global Services Received on Fri Oct 18 2002 - 12:36:38 CEST

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