Re: On specialization constraints time of application
Date: Sun, 14 Jun 2009 00:20:51 -0700 (PDT)
On 14 juin, 02:44, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "Cimode" <cim..._at_hotmail.com> wrote in message
> > On 13 juin, 19:26, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
> >> On Jun 10, 6:07 am, Cimode <cim..._at_hotmail.com> wrote:
> >> > > Since a TRDBMS should allow constraint specialization in a
> >> > > declarative way...
> >> IMO, TRDBMS is not a good term. First, why relational model applied to
> >> database management field only? Somewhere on databasecolumn.com I
> >> remember reading that Dr.Codd's initial intention was general purpose
> >> programming language; narrowing the scope to DBMS allowed to avoid
> >> competition with traditional PL.
> > Agreed.
> > By TRDBMS, I meant a system that allows an inner logical
> > representation that allows to operate soundly relations (thanks to a
> > relation declarative operating language) and that truly implements
> > independence between the physical and logical layers as defined
> > according to RM. TRDBMS is here to be understood as a hypothetic
> > objective for what a relational system (be it inside or outside the
> > scope of databases) should do.
> >> Also I consider the other TRDBMS features such as elimination of NULLs
> >> and duplicates as trivial. If there only for these one could challenge
> >> TRDBMS added value, which brings us to the TRDBMS crux feature --
> >> declarative constraints.
> > I wish I had your confidence. Since decomposition is the only correct
> > way to deal with missing information, I can tell you that buidling a
> > non direct image system that automatically decomposes relations and
> > implements Darwen approach to missing information is not what I would
> > call a trivial task. It took me one year to get this one to work.
> >> What are constraints? They are equations and inequalities in
> >> relational algebra, or some propositions in relational calculus.
> > Both have advantages that unfortunately mutually exclusive. RA has
> > stronger expressive power while RC allows better abstraction. I am
> > trying to get the best of both by developping a language whose
> > specifications I began to some monthes ago.
> The relational algebra and the calculus have equivalent expresive power,
> even when extended with aggregate functions. See
> "Equivalence of Relational Algebra and Relational Calculus Query Languages
> Having Aggregate Functions", Anthony Klug, Journal of the ACM, July, 1982.
> Incidentally, Date references this paper in the chapter on relational
> algebra in the eighth edition of /Introduction/.
Thanks. I never had a chance to pu my hands on this one. That is the next one on my bookself. Received on Sun Jun 14 2009 - 09:20:51 CEST