# Re: RM formalism supporting partial information

Date: Mon, 26 Nov 2007 04:12:42 -0800 (PST)

Message-ID: <306c9820-204f-4f93-adb4-684dc25af068_at_j20g2000hsi.googlegroups.com>

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