W3C home > Mailing lists > Public > public-rdf-wg@w3.org > November 2012

Re: Sloppy inference rules

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 1 Nov 2012 11:43:12 -0500
Cc: Markus Lanthaler <markus.lanthaler@gmx.net>, "'Guus Schreiber'" <guus.schreiber@vu.nl>, "'RDF WG'" <public-rdf-wg@w3.org>
Message-Id: <5C7F94CA-0BBD-46B9-BFCE-CBCC2DB349D1@ihmc.us>
To: Ivan Herman <ivan@w3.org>

On Nov 1, 2012, at 11:29 AM, Ivan Herman wrote:

> 
> On Nov 1, 2012, at 16:59 , Pat Hayes wrote:
> 
>> 
>> On Nov 1, 2012, at 5:13 AM, Ivan Herman wrote:
>> 
>>> It is not as clear-cut...
>>> 
>>> 1. There has been lots of discussions and controversies about this (although most of the controversies were on the literal-as-subject and not on the bnode-as-predicate issue). Ie, it is not just some simple editorial change. I have no idea what it would involve in terms of the RDF semantics
>> 
>> FWIW, the semantics would handle this without change. In fact, if RDF syntax were completely permissive (or possibly, only disallowing literals in predicate position) then the semantics would handle that without change. There is not, and never has been, any *semantic* requirement for these syntactic restrictions.
> 
> I was expecting this answer:-)

:-)

> I guess this is also true for OWL Full, which follows the same lines of semantics. But wouldn't it break OWL's Direct Semantics? (I guess that this could be handled by extra restrictions on RDF to be used with OWL DL, though

Yes, exactly. Anything less than Full will probably need to impose syntax restrictions in any case, even on current RDF. 

> , so it may be fine, too.)
> 
>> I would also point out that I have said this to the WG on numerous occassions and indeed also said it to the older WG on numerous occassions. 
>> 
>>> , let alone OWL. Also, apart from theoretical considerations, we have not seen huge demands from the community to add, say, bnodes as predicates.
>> 
>> True.
>> 
>>> 2. For the situation that Pat describes the issue is that a rule engine implementing the rules may (well, actually has to) have intermediate steps with triples that violate the restrictions on triples, but then export the valid triples only. I do not see any problem with this.
>> 
>> I agree there is no practical problem, but then I personally don't see any practical problem with allowing the syntax to be as permissive as the semantics. However, the fact that a reasoner needs to generalize the syntax in order to be complete is a kind of flashing neon sign, to anyone who knows logic, that there is a basic flaw in the design. Basically, RDF is designed so that it can express truths that it isn't allowed to derive, which is kind of brain-damaged.
> 
> I can see this point. However, my understanding is that a number of RDF environments, libraries, etc, have optimized along the lines of those restrictions. Changing this, ie, removing the restrictions in RDF 1.1, would lead to the necessity of major rewrites of existing systems. I would expect that to be a big no-no. 

Yes, I think that is the reason for retaining the restrictions. The problem with that line of thinking, however, is that this kind of too-expensive-to-change argument only becomes stronger as time goes on, so changes will *never* get made. And the counterargument is that allowing newer implementations to be more accepting does not invalidate the older implementations or make them less able to do anything they can do now. It just means that they can no longer claim to be covering all of the (now larger) language, which means that the argument is basically not even technical, but has to do with corporate advertising and image. 

Pat


> 
> Ie, this seems to be the case where theory clashes with the deployed reality:-(
> 
>> But I have come to accept that when working with the W3C, logically brain-damaged has to be considered to be par for the course. 
>> 
> 
> :-)
> 
> Ivan
> 
> 
>> Pat
>> 
>> 
>>> 
>>> Ivan 
>>> 
>>> 
>>> 
>>> On Nov 1, 2012, at 10:50 , Markus Lanthaler wrote:
>>> 
>>>> On Thursday, November 01, 2012 6:56 AM, Ivan Herman wrote:
>>>> 
>>>>> As Antoine notes, the OWL 2 group has faced the same issue for OWL 2
>>>>> RL. I do not see any problem doing that in this case either. I do not
>>>>> think we should reopen, at this point, the bnode-in-predicate and
>>>>> literal-in-subject issue and, with this, using this 'generalized
>>>>> triples for the rules' seems to be the clean approach...
>>>> 
>>>> Honestly it sounds a bit strange to me to simply accept that there is a
>>>> fundamental problem without trying to address it - especially considering
>>>> that the problem has been known since at least 2005 (2002?).
>>>> The other thing that worries me even more is the fact that a number of RDF
>>>> serialization formats are in the process of being standardized right now. At
>>>> least JSON-LD doesn't have this artificial restriction but that was heavily
>>>> criticized by the RDF WG and, as it seems at the moment, we will have to
>>>> introduce it.
>>>> 
>>>> I think there won't be a better point in time to fix this once for all.
>>>> 
>>>> 
>>>> Thanks,
>>>> Markus 
>>>> 
>>>> 
>>> 
>>> 
>>> ----
>>> Ivan Herman, W3C Semantic Web Activity Lead
>>> Home: http://www.w3.org/People/Ivan/
>>> mobile: +31-641044153
>>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>> 
>> ------------------------------------------------------------
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>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> FOAF: http://www.ivan-herman.net/foaf.rdf
> 
> 
> 
> 
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Thursday, 1 November 2012 16:43:50 GMT

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