Re: RM formalism supporting partial information
Date: Sun, 25 Nov 2007 23:53:41 -0400
Message-ID: <474a434a$0$5290$9a566e8b_at_news.aliant.net>
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. Received on Mon Nov 26 2007 - 04:53:41 CET