paul_geoffrey_brown_at_yahoo.com (Paul G. Brown) wrote in message news:<57da7b56.0310082211.79dca238_at_posting.google.com>...
> "Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message news:<Ze3hb.28$MU.214_at_news.oracle.com>...
> > "Paul G. Brown" <paul_geoffrey_brown_at_yahoo.com> wrote in message
> > news:57da7b56.0310081407.71d1bc8e_at_posting.google.com...
> > > mikharakiri_at_yahoo.com (Mikito Harakiri) wrote in message
> news:<bdf69bdf.0310080845.4d71a1f0_at_posting.google.com>...
> > > > paul_geoffrey_brown_at_yahoo.com (Paul G. Brown) wrote in message
> news:<57da7b56.0310080006.47b550a9_at_posting.google.com>...
> > > > > RELATION Dept ( Id Dept_Id KEY, Name String );
> > > > > RELATION Emp ( Id Emp_Id KEY, Dept REF(Dept),
> > > > > Name PersonName, Salary Money );
> > > > >
> > > > > RETRIEVE E.Name, DEREF(E.Dept).Name FROM Emp E;
> > > > >
> > >
> > > RETRIEVE E.Name FROM Emp E, Dept D
> > > WHERE DEREF(E.Dept).Id = D.Id AND D.Name = 'shoe';
> >
> > Now, suppose that indexed nested loops(D, E) is the best access path to the
> > data. Then DBA or advanced ("self-managed";-) DBMS would have to create
> > functional index on DEREF(E.Dept).Id. Then, wouldn't it be just be cleaner
> > to store Id instead of reference in the table itself?
>
> [ snip ]
>
> Well, the point of departure here was a discussion about modeling something
> at the logical level. Implementation is quite up to you. The simplest
> thing to do would be to take a bog-standard RDBMS approach and treat
> REF(Dept) as "this says to take the primary key of Dept and embed those
> columns invisibly within the Emp table and enforce the necessary RI
> constraint rules". At which point a decision about how to process this
> query becomes a bog-standard query problem.
>
> The biggest problems come about when you try to make REF() work in the
> absence of a primary key. At that point REF/DEREF goes really feral. In
> SQL-3 IIRC, there is this wierd thing where a column can ref to a key in
> more than one table but I'm not up to gospel on that.
>
> Look: 'logical pointers' done this way isn't new, and it isn't my idea.
> Carlo Zaniolo introduced the idea in a 1983 paper called GEM (or something
> like that). Besides, once again, I don't like RED/DEREF because it
> introduces redundant syntax.
It also violates the information principle.
Received on Thu Oct 09 2003 - 07:38:20 CDT
