On Wed, 24 May 2000, Chris Bitmead wrote:
> "Robert B. Easter" wrote:
> > Well, I hope some one sees my point about INHERITS and UNDER
> > maybe being complementary. UNDER is a single inheritance container/tree all
> > contained inside maximal supertable. INHERITS provides multiple inheritance
> > and can provide links between tables in different containers/trees, subject to
> > some restrictions. I think it deserves some looking at rather than just doing
> > away with INHERIT for just UNDER. (again I can be wrong). I guess its hard to
> > explain. I still need to provide good examples. I can best describe the
> > difference as UNDER creates circles within circles representing tables and
> > subtables. INHERITS provides for circles/tables to overlap (to be cloned in a
> > sense) and allows it multiple overlapping/merging. The INHERITS does it as it
> > is now that way, by merging same name attributes from two or more parents into a
> > single child. INHERIT is like cells reproducing using one or n parents.
> > UNDER is like a single cell making baby cells inside of itself. :-) hehe
>
> Would you still be having these thoughts if you were looking at the
> older SQL3 draft that included multiple inheritance UNDER? The newer
> UNDER appears to be a subset, which I presume they adopted to get the
> proposal out the door quicker. Personally I'd like to implement the
> SQL3-1994 extensions as well, because they actually seemed well thought
> out (I'm thinking particularly of the rename stuff).
There are documents at
ftp://jerry.ece.umassd.edu/isowg3/dbl/BASEdocs/sql4hold/
that maybe we should look at. It *might* represent what is planned for SQL4.
It shows UNDER accepting multiple supertables like the 1994 draft. However,
these documents are dated 1996 and probably don't really represent SQL4, which
might take many years still until its a standard. By the time SQL4 comes out,
there's no telling what it will look like.
I'm thinking, it might be best just to implement UNDER as it stands in the
official standard for now. Leave INHERIT the way it is (for the most part) and
implement UNDER separately. Continue to use inherit if you need multiple
inheritance. If you implement multiple inherit UNDER, it will create a user
base that will depend on that functionality. Later, it will be difficult to
change that functionality if the official standard for UNDER does switch to
multiple inheritance but in a way that is incompatible with yours. Its not a
good idea to second guess the future standard. People already use INHERIT the
way it is and it can be used in combination with UNDER.
--
Robert B. Easter
reaster@comptechnews.com
