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Re: BLD issue: non-disjointness of internal and external predicate symbols

From: Chris Welty <cawelty@gmail.com>
Date: Mon, 14 Jul 2008 09:43:56 +0200
Message-ID: <487B03BC.7090706@gmail.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: Jos de Bruijn <debruijn@inf.unibz.it>, kifer@cs.sunysb.edu, RIF <public-rif-wg@w3.org>


This appears to be unresolved.  I see the problem Jos points out, that you can 
have the same symbol (and most problematically I guess if its the same URI) that 
*could* syntactically denote both an external predicate and an internal one. 
This *seems* to violate the design of the semantic web (URIs are rigid designators).

</chair>
Personally, I think the internal/external distinction is outside the scope of 
the semantic web anyway, so I don't think this matters.  I am happy to leave it 
as is.  It merely *allows* one to use the same symbol in different RIF contexts, 
it doesn't require it.
<chair>

Anyway, we need to wrap this up.  Were you OK with things as they are, Jos?

-Chris

Axel Polleres wrote:
> 
> Jos de Bruijn wrote:
>> Michael,
>>
>> My argument is not about error-checking, but rather about the 
>> principle that the same constant you use in different places should 
>> mean the same thing.
>>
>> But I'm also willing to compromise for the case of external frames, so 
>> the compromise would be:
>>
>> - we create additional sets for external functions and predicates that 
>> are disjoint from the sets of "internal" symbols, and impose the 
>> condition that internal function and predicate symbols may not be used 
>> in external terms
>> - we do not impose restrictions on symbols used in external frames
>>
>> Let's see what the rest of the working group thinks about this.
> 
> Why do we need to make this restriction? It doesn't seem to buy us 
> anything, as semantically, the external funcs and preds are well 
> separated from the internal ones, so, no danger.
> 
> Axel
> 
> 
>> Best, Jos
>>
>> Michael Kifer wrote:
>>>
>>> On Thu, 10 Jul 2008 17:03:25 +0200
>>> Jos de Bruijn <debruijn@inf.unibz.it> wrote:
>>>
>>>>
>>>> Michael Kifer wrote:
>>>>> This was not an omission, but I am fine with separating external from
>>>>> non-external symbols for functions and predicates. 
>>>> ok, good
>>>>
>>>>  > As to the frames, I do not think any of the symbols
>>>>> should be required to be external.
>>>> But then the same constant used in different contexts has a 
>>>> different meaning, which I think was something we were trying to 
>>>> avoid in BLD.
>>>
>>> Frames are reflexive by nature. So, in some other statement you may 
>>> want to
>>> say that some object (even external one) has a particular set of 
>>> properties and
>>> list them).
>>>
>>> Frankly, I do not understand why is it a deal to allow the same, say 
>>> predicate,
>>> to appear inside External(...) and outside of it. The reason for 
>>> separating the
>>> symbols was to ease the interface with FOL. But separating external and
>>> non-external symbols does not affect that.
>>>
>>> Syntactically it is clear whether a symbol is used as external or 
>>> internal, and
>>> I see no reason to reinforce this with an additional syntactic kludge (I
>>> conceded it just in the interests of peace :-).  If your argument is
>>> error-checking then it is not our business. Systems that care about 
>>> it would
>>> build the appropriate error checkers.
>>>
>>>
>>>     --michael
>>>> Best, Jos
>>>>
>>>>>
>>>>>
>>>>>     --michael
>>>>> On Thu, 10 Jul 2008 12:57:45 +0200
>>>>> Jos de Bruijn <debruijn@inf.unibz.it> wrote:
>>>>>
>>>>>> There is an issue in BLD, which I unfortunately did not catch 
>>>>>> before.  I think it is probably an omission in the definition, but 
>>>>>> it is a substantive one.
>>>>>> If we all agree that it is indeed an omission, we can probably 
>>>>>> address the problem, create a new frozen version, and vote about 
>>>>>> publication in the next phone conference on Tuesday.
>>>>>> Personally, I am not ready to sign off on publication before this 
>>>>>> issue is resolved.
>>>>>>
>>>>>> The issue is the following: in the definition of well-formed 
>>>>>> terms, the set of all symbols is partitioned into predicate 
>>>>>> symbols, function symbols, etc. however, no distinction is made 
>>>>>> between external and "internal" symbols.  The consequence is that 
>>>>>> the same function or predicate symbol can be used both in an 
>>>>>> external term and an internal term, and these two terms have 
>>>>>> different meanings, i.e., the same constant is interpreted 
>>>>>> differently based on the context, which is something we explicitly 
>>>>>> wanted to avoid in BLD.  So, a built-in function may be used 
>>>>>> outside an external term and will be uninterpreted.
>>>>>>
>>>>>> The problem is easy to fix by defining additional sets of external 
>>>>>> predicate function symbols that are disjoint from the other sets 
>>>>>> of symbols and defining appropriate restrictions on external terms 
>>>>>> (i.e., the first function/predicate symbol in an external term 
>>>>>> must be an external symbol).
>>>>>> It becomes a bit more tricky when considering external frames, but 
>>>>>> probably all constants used in an external frame should be 
>>>>>> external individuals/functions/predicates.
>>>>>>
>>>>>> Best, Jos
>>
> 
> 

-- 
Dr. Christopher A. Welty                    IBM Watson Research Center
+1.914.784.7055                             19 Skyline Dr.
cawelty@gmail.com                           Hawthorne, NY 10532
http://www.research.ibm.com/people/w/welty
Received on Monday, 14 July 2008 07:44:44 GMT

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