Re: RM formalism supporting partial information
Date: Mon, 26 Nov 2007 04:12:42 -0800 (PST)
On 26 nov, 04:53, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Jan Hidders wrote:
> > 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).
> It strikes me that 6NF (or at least good designs that do not try to
> shoehorn relations with heterogeneous relative cardinalities into a
> single base relvar) plus views provide exactly that sort of explicitness.
Only for the "value does not apply" interpretation of null values and that wasn't really a big problem in the first place.
- Jan Hidders