Re: RM formalism supporting partial information
From: paul c <toledobythesea_at_ooyah.ac>
Date: Wed, 28 Nov 2007 13:24:26 GMT
Message-ID: <e_d3j.62082$cD.25240_at_pd7urf2no>
>
> I believe there is a terminology problem here concerning the terms
> "possible answers" and "certain answers". In the context of research
> on incomplete databases (i.e. anywhere the classical CWA does not
> apply fully) that usually means the following. Given a query and the
> assumptions about "closedness" the set all tuples with the right
> header can be partitioned into three groups: the certain answers
> (those that are certain to be in the result of the query on the
> omniscient database), the possible answers (those that might be in the
> aforementioned result) and the impossible answers (those that are
> certain not to be in the aforementioned result).
>
> In that sense the tuple describing the person you mentioned above
> (presuming it is projected on the non-null fields) is a certain
> answer, not a possible answer.
> ...
Date: Wed, 28 Nov 2007 13:24:26 GMT
Message-ID: <e_d3j.62082$cD.25240_at_pd7urf2no>
Jan Hidders wrote:
> On 28 nov, 01:58, David BL <davi..._at_iinet.net.au> wrote:
...
>> Consider a query to find all the 27 year old pilots from a census >> recorded in an RDB. If the age or occupation is missing we could >> think of the person as a possible answer.
>
> I believe there is a terminology problem here concerning the terms
> "possible answers" and "certain answers". In the context of research
> on incomplete databases (i.e. anywhere the classical CWA does not
> apply fully) that usually means the following. Given a query and the
> assumptions about "closedness" the set all tuples with the right
> header can be partitioned into three groups: the certain answers
> (those that are certain to be in the result of the query on the
> omniscient database), the possible answers (those that might be in the
> aforementioned result) and the impossible answers (those that are
> certain not to be in the aforementioned result).
>
> In that sense the tuple describing the person you mentioned above
> (presuming it is projected on the non-null fields) is a certain
> answer, not a possible answer.
> ...