Re: Are there terms for these?

From: Kenneth Downs <knode.wants.this_at_see.sigblock>
Date: Thu, 25 Aug 2005 16:34:27 -0400
Message-Id: <thm1u2-9r.ln1@pluto.downsfam.net>

Marshall Spight wrote:

> Kenneth Downs wrote:

>> Marshall  Spight wrote:
>>
>> > Kenneth Downs wrote:
>> >> Given two tables that are not UNION compatible, it seems there are
>> >> ways to UNION them anyway.
>> >>
>> >> Method 1, Intersect their headers.  The resulting header is used to
>> >> project
>> >> both tables and now those projections are union compatible.  What
>> >> would this be called?
>> >
>> > We've been discussing this a lot. There was even a thead I started
>> > about
>> > a month ago called (IIRC) What would this operator be called?
>>
>> This is scary, how did I miss it?

>
> Here it is:
>
> "What to call this operator?"

>
http://groups.google.com/group/comp.databases.theory/browse_thread/thread/7a855309c23c73eb/1aad918848dd35fd

This is very sad. I found the topic incomprehensible and was not following closely. Now I'll have to go back.

>
> In the opening post on that thread, I ask what we should call these
> generalized union operations. I actually speak directly in terms
> of the TTM <AND> and <OR> because I thought that'd be more familiar
> to a wider readership. However, what I really had in mind was the
> exact operator you described above, in which the values that have
> to be "made up" are more null-like than infinite-like. Specifically,
> I've been going with a 2VL in which certain attributes may take
> on the empty set, as a replacement for null.
>
> Since then, (specifically as a result of that thread) I've
> become aware of Vadim Tropashko's paper "Relational Algebra as
> Non-Distributive Lattice" in which he describes the *inner*
> union, and manifold ways it's mathematically interesting.
> I'm not so interested in outer union any more.
>
>

>> > Since then, I've been going with "inner union" or "generalized union".
>>
>> What's weird is that normally somebody jumps in and points out that these
>> ideas were first worked out in Sanskrit thousands of years ago and we
>> should RTFM.  How can it be that no terms exist and you are making them
>> just now?

>
> I would like to take this opportunity to apologize on a personal
> level for not heaping abuse on you in the manner to which you
> have become acustomed.

:)

>
>

>> >> Method 2, Union their headers.  The resulting header is used to UNION
>> >> both tables, providing NULL or empty values where a column exists in
>> >> one but not
>> >> the other.  What would this be called, a FULL OUTER UNION (ha ha)?
>> >
>> > I'm calling it "outer union."
>>
>> I suppose there really would be a LEFT OUTER UNION and a RIGHT OUTER
>> UNION,
>> though.  Left would be all columns from table 1 plus common columns 1 and
>> 2, or:
>>
>> (L n R) U L   (that 'n' is supposed to be intersection)
>>
>> and RIGHT OUTER UNION would be all columns from right plus common
>> columns, or:
>>
>> (L n R) U L

>
> I'm not so happy with the idea of asymmetric operators lately.
> They seem like a sign of bad design.

interesting.

>
> Anyway, read the thread and the Tropashko paper. It just might
> blow your mind; it blew mine.
>
>
> Marshall

-- 
Kenneth Downs
Secure Data Software, Inc.
(Ken)nneth@(Sec)ure(Dat)a(.com)

Received on Thu Aug 25 2005 - 15:34:27 CDT