Re: Character string relation and functional dependencies

Jan Hidders <hidders_at_gmail.com> wrote in news:dd39930a-d971-43a1-8d13-779cd635f632_at_s8g2000prg.googlegroups.com:

> On 7 dec, 01:24, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:

>> On Dec 6, 2:38 pm, Jonathan Leffler <jleff..._at_earthlink.net> wrote:
>>
>> > Tegiri Nenashi wrote:
>> > > On Dec 6, 9:40 am, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:
>> > >> Another difference is that database tables are finite and
>> > >> variable, 
>>
>> > > Oh, relations in database world are certainly not restricted by
>> > > finite cardinality.
>>
>> > I thought that computers are finite, so the relations containable
>> > in them are too - even if damn large.  There's a big difference
>> > between very large and infinite.
>>
>> This doesn't really matter. You can still reason about infinite
>> relations with finite resources available on you computer platform.

This kind of "reasoning" is an illusion. The constraint database the link refers to works with a finite set of first-order formulas ("extended tuples") that permit quantifier elimination rather than with a finite set of actual tuples as the relational model would. It is a simple observation that a first-order formula under certain conditions can "represent" a possibly infinite set. However, formula-set interpretation happens in the user brain only, not in the database itself as would be the case with the traditional relational model which probably explains along with other problems why constraint databases do not enjoy much success.

>
> http://cse.unl.edu/~revesz/cdb/index.htm
>
> -- Jan Hidders
Received on Mon Dec 10 2007 - 02:09:08 CET