SQL is basically a conjunctive normal form query language that can be used
to find individuals in a prescribed universe. It does not provide rules of
inference. If a query returns no results, it is not possible to tell whether
the query was inconsistent or there happened to be no individuals in the
database that satisfy the query. The "open world" semantics of the
description logics make query satisfaction quite a bit more difficult.
Thanks, Jim (01)
-----Original Message-----
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Christopher
Menzel
Sent: Thursday, December 17, 2009 12:12 PM
To: [ontolog-forum]
Subject: Re: [ontolog-forum] blogic iswc keynote (02)
On Dec 16, 2009, at 2:27 PM, sowa@xxxxxxxxxxx wrote:
>> RM> Would you have a recommendation for generating representations that's
a bit more agile than crocheting?
>
> Please remember that CLIF and CGIF have been designed as *interchange
formats* for an open-ended number of different, but compatible kinds of
logics. Every implementation of any one of those subsets *is* an
implementation of Common Logic.
>
> I noticed that in the Q/A section of Pat's talk, somebody said that CL is
too expressive -- therefore, it is inefficient.
>
> But that question is hopelessly confused. (03)
Agreed. (04)
> It is based on the assumption that there is *one and only one* method of
using or reasoning with any given logic. But that assumption does not hold
for *any* natural language, programming language, query language, or,
indeed, any version of logic. (05)
It's not clear to me that that is necessarily being assumed. Another
possibility is that the questioner believes that representation languages
should be *paternalistic* -- that is, they should prevent users from even
posing questions that are undecidable. OWL-DL is of course the best known
language of this sort. It seems to me that it makes sense to have such
languages for a certain class of user who is not wise in the ways of
computational complexity. However, to take the responsibilities of managing
complexity from all users of any representation language and instead impose
this paternalistic restriction on languages in general (not to mention
interchange formats) makes no sense at all. (06)
However, I am confused by one thing you wrote: (07)
> For database queries and constraints, SQL supports full FOL, but even the
worst case examples can be evaluated in polynomial time, (08)
I am probably not understanding the claim, but how is this possible if SQL
supports full FOL, in which we can easily express problems that can be
solved, if at all, in at best exponential time? (09)
-chris (010)
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