Re: Lucid statement of the MV vs RM position?
Date: Wed, 26 Apr 2006 11:31:30 -0700
On 25 Apr 2006 17:59:04 -0700, "Pickie" <keith.johnson_at_datacom.co.nz> wrote:
>Multivalues can violate first normal form in the same way as using the
>internal file, block, and row numbers instead of a key violates Codd's
>guaranteed access rule. That is to say, while it may be possible to do
>something, it may not be good practice to do it. Multivalues are
>correctly used if they are seen as a compact storage method for 'child'
>relations. They partially automate cascading deletes which otherwise
>would require application programming.
And require application programming to unpack.
>In my opinion, MV databases tend to collect rubbish data, but the
>applications do not fail catastrophically because of this. Usually the
Sure, they just give wrong answers. People base their decisions on these wrong answers. It may not be realistically possible to track back to exactly what caused a bad decision. Bad data is often involved though.
>rubbish is only discovered when migrating the data to a DBMS, or
>investigating the possibility of doing so. Obviously, these ones are
>not quite "as good as a relational DBMS". However, this cruft seems to
>gather as the conceptual model evolves, so maybe at one point it was
>"as good as".
Or maybe it never was.
Gene Wirchenko Received on Wed Apr 26 2006 - 20:31:30 CEST