Re: Requirements for update languages?

"Jens Lechtenbörger" <lechtej_at_uni-muenster.de> wrote in message news:m2wunmmkda.fsf_at_pcwi1068.uni-muenster.de...
> "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> writes:
>
> > "Jens Lechtenbörger" <lechtej_at_uni-muenster.de> wrote in message
> > news:m2k7jo87eh.fsf_at_pcwi1068.uni-muenster.de...
> > > Dear reader,
> > >
> > > while there are some criteria to assess relational query languages
> > > (adequate, relationally complete, optimizable) I wonder what makes a
> > > good update language for a data model.
> > >
> > > In particular, I wonder about the following points in SQL.
> > >
> > > 1. I believe that SQL data manipulations are not adequate for bags,
> > > as they lack the ability to manipulate duplicates. (E.g., you
> > > can neither delete 3 out of 5 duplicates nor insert 3 duplicates
> > > at once.)

SQL has many flaws. Support for bags is one of its primary flaws. Whether it supports them well is secondary and frankly unimportant. No improvement in the support for bags will overcome the serious harm caused by a lack of logical identity and by violation of the information rule.

> > > 2. As a db user, I expect that I can undo (inadvertent) data
> > > manipulations, e.g., undo an insertion via a deletion or vice
> > > versa.
> > > Does anybody else believe that this is a reasonable requirement?
> >
> > No, I believe that is highly unreasonable. I you buy 5,000,000
> > shares you cannot just say, opps, didn't mean to do that -
> > backout, you must sell them and hope you don't loose money.
>
> OK. I want to have the ability to undo my updates *in theory*.
> Practical, legal, whatever issues might prevent me from actually
> undoing them.

In theory, if I burn a block of wood, can I reverse the process to get my original block of wood back? It would seem to me that you want to have your cake and to eat it too.

Both in theory and in practice, some things are reversible and some things are not. As they say about light bulbs and pregnant women, one can unscrew a light bulb.

> > > 3. As a db admin, I expect that users know what they are doing when
> > > they manipulate data.
> > > Does anybody else believe that this is a reasonable requirement?
> >
> > No, I believe that is highly unreasonable. If all my database
> > users had to pass am exam before using the db and had to sign a
> > legally enforceable grantee that they know what they are doing,
> > then I would not have very many db users. ;-)
>
> So, it's "highly unreasonable" because you could loose your job?

No. It's highly unreasonable because all human beings are fallible--even the most intelligent and the best trained.

If it were reasonable to assume that users always know exactly what they are doing (and always mean well), we would have no need for referential integrity constraints, trigger locks, seatbelts or jails.

> > > Basically, the anonymous referees did not buy (2) and (3).
> >
> > I don't blame them.
>
> When writing up another posting in this thread, where I summarized
> the critique, I realized that only 1 out of 4 did not by (2) and
> (3). 1 did, the other 2 seemed to expect more theorems for that
> conference.

At least you were fortunate enough to have one sensible, informed and forthright referee. In the data management industry, such folks are actually far rarer than 25% of the population. Received on Sun Nov 10 2002 - 04:03:08 CET