Re: RM formalism supporting partial information
Date: Mon, 26 Nov 2007 06:36:31 -0800 (PST)
Message-ID: <6002a9cb-b0a6-4509-8475-de3b0ea1cd36_at_e4g2000hsg.googlegroups.com>
On Nov 26, 2:06 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> "Jan Hidders" <hidd..._at_gmail.com> wrote in message
>
> news:9f987d7d-009c-451c-969f-16bade1d5c53_at_s36g2000prg.googlegroups.com...
>
> > On 24 nov, 23:34, Marshall <marshall.spi..._at_gmail.com> wrote:
> > > On Nov 23, 10:56 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > > > Exactly, so in that sense it is actually complete, and you can make
> > > > that claim precise. The set of tupels in the answer will be exactly
> > > > the set of tuples that are certain to be in the result of the same
> > > > query over the omniscient database. By the nature of the problem every
> > > > query should actually return 2 sets of tuples: the set of certain
> > > > answers, and the set of possible answers. Your operators should
> > > > therefore not operator on relations but on pairs of relations.
>
> > > It seems to me that anything that we can say about partial
> > > information can be said with total information. In other words,
> > > efforts at making the *system* understand partial information
> > > are merely pushing systemward calculations that could be done
> > > in a system without any understanding of partial information.
>
> > > If so, it seems to me the best we can hope for with such
> > > an effort is some additional convenience. At which point,
> > > any justification for a system with built-in support for
> > > partial information *must* be done in terms comparing
> > > the convenience of queries, processing, etc. with vs.
> > > without the new partial-info primitives. I don't recall having
> > > seen this done however.
>
> > > An analogous situation applies with approximate calculations.
>
> > > I would be interested to hear anyone agree or disagree.
>
> > I largely agree but would add that if done well the support for
> > incomplete information would help and/or force you to be more explicit
> > about what your data means (e.g. in making explicit which CWA where
> > applies) and what the answers to you queries mean (e.g. only the
> > certain answers or also the possible answers, or something else).
>
> I think that in order to be done well the theory of incomplete information
> needs to be split out into two sub theories. I hesitate to name them. One
> would be the theory of storage and retrieval of incomplete information in
> databases and the like. The other would be about the processing of data in
> the face of incomplete information, or approximate information.
>
> This split occured in the area of data in general about 1970, with Codd's
> paper. Database theory is not a general theory of computing, dressed up in
> database clothing. There's no reason why the theory of incomplete
> information should be different.
>
> > -- Jan Hidders
Received on Mon Nov 26 2007 - 15:36:31 CET