Requirements for update languages?

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.)
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?

   First, it is not clear whether this is true for base    relation updates. E.g., consider relation R(A,B) with an    assertion "check 2 < select count(*) from R where A=1" in bag    instance { (1,0), (1,0), (1,0) } and insertion of (1,0) into this    instance. As duplicates are not treated well by SQL, an undo of    that insertion is difficult. I guess that the only way is to    issue a transaction that first deletes everything and then    re-inserts the desired tuples. Clearly, this works in theory,    but is not a desirable way to go in practice.    Second, in the presence of view updates, problems arise much more    naturally (without duplicates). E.g., users cannot undo    deletions from projections, as information about the missing    attributes is not available.

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?

   Again, for view updates this is often not the case. E.g., in case    of projections users delete tuples they do not know completely;    in case of deletions from unions they do not even know from which    relation something gets deleted.

It turns out that (2) and (3) above are equivalent. I wrote a paper about this issue, where I warn against using view updates. If you are interested, take a look at:
http://dbms.uni-muenster.de/publications/downloads/view-updates.pdf A small warning: An almost identical version of that paper got rejected at ICDT'03. Basically, the anonymous referees did not buy
(2) and (3).

I'm curious to see your opinions.

Jens Received on Fri Nov 08 2002 - 15:26:14 CET