Re: OO Patch

From: Hannu Krosing <hannu(at)tm(dot)ee>
To: Oliver Elphick <olly(at)lfix(dot)co(dot)uk>
Cc: Marten Feldtmann <marten(at)feki(dot)toppoint(dot)de>, Postgres Hackers List <hackers(at)postgresql(dot)org>, olly(at)linda(dot)lfix(dot)co(dot)uk
Subject: Re: OO Patch
Date: 2000-05-22 21:07:32
Message-ID: 3929A194.599D0091@tm.ee
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

Oliver Elphick wrote:
>
> Marten Feldtmann wrote:
> >> Hannu Krosing wrote:
> >> >
> >> >but as E can be an INT in one subclass and TIMESTAMP or VARBINARY in
> >> >other
> >>
> >> I don't think that should be allowed. It violates inheritance principles,
> >> since the types are not compatible.
> >
> > I see ... here's a person who has always programmed with typed
> >languages and now thinks, that this is the right definition .... it's
> >much more out there in the world. Open your mind and think about the
> >following:
> >
> > An attribute named "a" of "type" TIMESTAMP of an instance of a class
> >can be seen as a relation from this class to the class TIMESTAMP and
> >this relation is named "a".
> >
> > And if you're on the way to relations you're not far away to see,
> >that a relation is of course not limited to show to one specific class
> >... but perhaps to all subclasses also ... and this is not a
> >violation.
>
> However the example I was referring to talked of INT4, TIMESTAMP or VARBINARY.
>
> These are not subclasses but totally unrelated. Suppose you had
>
> parent (id char(2))
> child1 (a int4)
> child2 (a timestamp)
>
> and someone asks for
>
> select sum(a) from parent*
>
> since the types are incompatible, the answer would be nonsense.

MS Excel for example SUMs only things summable, by which logic in this
case
the sum would/could/should be sum of int4 colums.

In real world not all things are summable.

OTOH for schema
parent (id char(2))
child1 (a orange)
child2 (a apple)

select sum(a) from parent*

could yield "N apples and M oranges" or possibly "X fruits" if orange
and
apple were subtypes of fruit. Yes, really ;)

Or depending on how the sum() function is defined it could even be "Y
kg" .

---------
Hannu

In response to

Browse pgsql-hackers by date

  From Date Subject
Next Message Murad Nayal 2000-05-22 21:12:51 Re: [BUGS] port v7.0 to SGI-IRIX-6.5.7/64
Previous Message Oliver Elphick 2000-05-22 20:58:21 Re: OO Patch