Re: RM formalism supporting partial information

From: Bob Badour <>
Date: Mon, 26 Nov 2007 11:19:53 -0400
Message-ID: <474ae41e$0$5268$>

Jan Hidders wrote:

> On 26 nov, 04:53, Bob Badour <> wrote:

>>Jan Hidders wrote:
>>>On 24 nov, 23:34, Marshall <> wrote:
>>>>On Nov 23, 10:56 am, Jan Hidders <> 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.

I fail to see the relevance of null markers. Not using them obviates interpretation. Received on Mon Nov 26 2007 - 16:19:53 CET

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