[ontolog-forum] Logic, Datalog and SQL

["Adrian Walker" <adriandwalker@xxxxxxxxx>]

Hi John --

You wrote...

Datalog, for example, is a cleaned up version of the SQL query language with the extension of
allowing recursive definitions.

Well, that's an approximate idea.  However, the following would be more accurate:

   "datalog+closed world negation allowing some recursive definitions is a cleaned up version of SQL minus aggregations" 

Actually, if there is to be a new Wikipedia or other encyclopedia entry on logic for ontologies, it should summarize the ongoing debate between the "closed" and "open" world negationist camps.  Almost all uses of databases in our everyday life rely on things like "if it's not in the catalog we don't stock it", "if no flight number to Podunk is in the database, then there is no flight to Podunk", so we should not ignore closed world usage of databases just because the clasical logicians never wrote about it.

                                     Cheers,   -- Adrian

PS:  There is of course a model theory for stratified datalog plus closed world negation.  See e.g.
         Backchain Iteration: Towards a Practical Inference Method that is Simple 
  Enough to be Proved Terminating, Sound and Complete. Journal of Automated Reasoning, 11:1-22.  

Internet Business Logic (R)
A Wiki for Executable Open Vocabulary English
Online at www.reengineeringllc.com
                                Shared use is free
Adrian Walker
Reengineering

On 2/8/07, John F. Sowa <sowa@xxxxxxxxxxx> wrote:

Conrad,

I haven't had a chance to read the document in detail,
but it looks like a good summary of a lot of issues.

> Would be glad for any comments or corrections.

I don't know how much time you or your coauthors have
to do anything further, but it would be helpful to have
more examples.  That would make it more accessible to
people with a modest background in logic.  Otherwise,
it is only readable by people who are beyond the
introductory stage.

For some entries, the discussion is too brief to indicate
the importance.  Datalog, for example, is a cleaned up
version of the SQL query language with the extension of
allowing recursive definitions.  That makes it an excellent
basis for linking a reasoning system to relational DBs.
A couple of extra lines to make such points would be helpful.

One minor point that struck me as I was flipping pages:

> Terms refer to objects in the domain, such as John or Mary.

I had to do a double take, because it sounds as if the character
strings are objects in the domain.  It would be clearer to say

   Terms, such as "John" or "Mary", refer to objects in the domain.

John






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