Re: Requirements for update languages?
Date: Mon, 11 Nov 2002 13:26:46 -0500
"Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> "Jens Lechtenbörger" <lechtej_at_uni-muenster.de> wrote in message
> > > General comment on bags: There are no such things.
> > Just to settle the issue: They exist. I created them in IBM DB2
> > UDB. You work at IBM, don't you? ;)
> Depends what you call a bag. Duplicate rows in SQL tables not *identical
> all respects*, it's just that you have choosen to hide the piece(s) of
> information that distinguishes
> I might work for IBM, but I can't be blamed for SQL.
Sure you can. Blaming the innocent is as easy as pie, and it happens all the time. If you doubt me, just ask around at work.
> > > If two things are *identical in all respects* then they *are the
> > > same thing*. If they are not identical in all respects and you
> > > choose to hide the piece(s) of information that distinguishes
> > > them, then you break the information principle and frankly deserve
> > > what you get.
> > In tables I don't need to represent "all respects". The easiest
> > example I can think of is my *bag* of items bought in a supermarket.
> > It might contain two boxes of beer (if it was big enough for boxes
> > of beer, of course). I don't care to tell them apart
> You do care insofar as you need to know that when you have counted one of
> them, you only have one more left to count. If you care that there are
> beers, you need to be able to tell them apart.
I found your explanation a little abstract. Consider this example instead:
I have two boxes of beer that are indistinguishable in all respects. Now, I am a big guy but two boxes of beer is more than I need before I get my next paycheque. Let's say I am willing to trade one of those boxes of beer for a ride to the party and a blind date with the driver's girlfriend's best friend. (They tell me she's nice.)
The last bit worries me a little, and when I get to the party, I want to make sure I have at least one box of beer with me -- just in case.
If the boxes of beer are indistinguishable in all respects, how do I give away one box of beer without giving away both of them?
Having some difficulty, I try to see if an application view will help so I cover my left eye with the palm of my left hand. (Hey, it helped for deduping a couple times in the past so what the heck, eh.) Unfortunately, the view doesn't seem to help much.
> > In contrast, arguments like (1.) in my original posting above should
> > help people see why bags in SQL are a bad idea.
> Fair enough, but I think we have plenty of evidence already.
> Hands up who thinks bags are a good idea.
Will that be paper or plastic? Received on Mon Nov 11 2002 - 19:26:46 CET