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Re: Subjects as Literals, [was Re: The Ordered List Ontology]

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 2 Jul 2010 10:11:19 -0500
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <A23EA5E7-D5D9-4FB9-98A4-6228863F3F7C@ihmc.us>
To: Kingsley Idehen <kidehen@openlinksw.com>

On Jul 2, 2010, at 6:52 AM, Kingsley Idehen wrote:

> Pat Hayes wrote:
>>
>> On Jul 1, 2010, at 9:42 AM, Kingsley Idehen wrote:
>>
>>> Pat Hayes wrote:
>>>>
>>>> On Jun 30, 2010, at 3:49 PM, Kingsley Idehen wrote:
>>>>
>>>>> Pat Hayes wrote:
>>>>>>
>>>>>> On Jun 30, 2010, at 1:30 PM, Kingsley Idehen wrote:
>>>>>>
>>>>>>> Nathan wrote:
>>>>>>>> Pat Hayes wrote:
>>>>>>>>> On Jun 30, 2010, at 6:45 AM, Toby Inkster wrote:
>>>>>>>>>> On Wed, 30 Jun 2010 10:54:20 +0100
>>>>>>>>>> Dan Brickley <danbri@danbri.org> wrote:
>>>>>>>>>>> That said, i'm sure sameAs and differentIndividual (or  
>>>>>>>>>>> however it is
>>>>>>>>>>> called) claims could probably make a mess, if added or  
>>>>>>>>>>> removed...
>>>>>>>>>>
>>>>>>>>>> You can create some pretty awesome messes even without OWL:
>>>>>>>>>>
>>>>>>>>>> # An rdf:List that loops around...
>>>>>>>>>>
>>>>>>>>>> <#mylist> a rdf:List ;
>>>>>>>>>>     rdf:first <#Alice> ;
>>>>>>>>>>     rdf:next <#mylist> .
>>>>>>>>>>
>>>>>>>>>> # A looping, branching mess...
>>>>>>>>>>
>>>>>>>>>> <#anotherlist> a rdf:List ;
>>>>>>>>>>     rdf:first <#anotherlist> ;
>>>>>>>>>>     rdf:next <#anotherlist> .
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> They might be messy, but they are *possible* structures  
>>>>>>>>> using pointers, which is what the RDF vocabulary describes.   
>>>>>>>>> Its just about impossible to guarantee that messes can't  
>>>>>>>>> happen when all you are doing is describing structures in an  
>>>>>>>>> open-world setting. But I think the cure is to stop thinking  
>>>>>>>>> that possible-messes are a problem to be solved. So, there  
>>>>>>>>> is dung in the road. Walk round it.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Could we also apply that to the 'subjects as literals'  
>>>>>>>> general discussion that's going on then?
>>>>>>>>
>>>>>>>> For example I've heard people saying that it encourages bad  
>>>>>>>> 'linked data' practise by using examples like { 'London' a  
>>>>>>>> x:Place } - whereas I'd immediately counter with { x:London a  
>>>>>>>> 'Place' }.
>>>>>>>>
>>>>>>>> Surely all of the subjects as literals arguments can be  
>>>>>>>> countered with 'walk round it', and further good practise  
>>>>>>>> could be aided by a few simple notes on best practise for  
>>>>>>>> linked data etc.
>>>>>>>
>>>>>>> IMHO an emphatic NO.
>>>>>>>
>>>>>>> RDF is about constructing structured descriptions where  
>>>>>>> "Subjects" have Identifiers in the form of Name References  
>>>>>>> (which may or many resolve to Structured Representations of  
>>>>>>> Referents carried or borne by Descriptor Docs/Resources). An  
>>>>>>> "Identifier" != Literal.
>>>>>>
>>>>>> What ARE you talking about? You sound like someone reciting  
>>>>>> doctrine.
>>>>>>
>>>>>> Literals in RDF are just as much 'identifiers' or 'names' as  
>>>>>> URIs are. They identify their value, most clearly and  
>>>>>> emphatically. They denote in exactly the same way that URIs  
>>>>>> denote. "23"^^xsd:number   is about as good an identification  
>>>>>> of the number twenty-three as you are ever likely to get in any  
>>>>>> notational system since ancient Babylonia.
>>>>>
>>>>> Yes, but ancient Bablyonia != World Wide Web of Structured  
>>>>> Linked Data, slightly different mediums with some shared  
>>>>> characteristics :-)
>>>>>
>>>>> The World Wide Web is becoming a Distributed DBMS (in my eyes).  
>>>>> Thus, unambiguous naming matters.
>>>>
>>>> A topic for a longer discussion; but irrelevant here, since typed  
>>>> literals are as unambiguous as a name can possibly get.
>>>>
>>>>>
>>>>> Literal Subjects aren't a "show stopper" per se. (esp. for local  
>>>>> RDF data). My gripe simply boils down to the nuisance factor  
>>>>> introduced by data object name ambiguity in a distributed data  
>>>>> object oriented realm such as the emerging Web of Linked Data.
>>>>>
>>>>> What does ""23"^^xsd:number " mean to anyone in a global data  
>>>>> space?
>>>>
>>>> It means the number twenty-three, everywhere and for all time,  
>>>> because this meaning can be computed from the very syntactic form  
>>>> of the name. How unambiguous can something get?
>>>
>>> Pat,
>>>
>>> Re. RDF's triples, What is a Subject? What is an Object?.
>>
>> "subject' refers to the first element in a triple, "object" to the  
>> last. One might as well call them 'first' and 'third'. The names
>> 'subject' and 'object' are used purely for convenience, and have no  
>> formal or semantic significance.
>>
>>>
>>> If they are the same thing, why on earth do we use Names (with  
>>> implications) to describe the slots in an RDF triple?
>>
>> I do not understand the question here well enough to provide an  
>> answer. Have you actually read the RDF spec documents? The RDF  
>> syntax model and the semantics?
>
> You don't understand the question enough to provide an answer, but  
> you are able to compute an assessment of spec assimilation. WOW !!

The logic here is: if you had understood the specs, you wouldn't be  
asking such a damn silly question as you appear to be asking. So, I  
conclude to myself, I must be misunderstanding your question. Unless,  
of course, you havn't actually read the specs...

>>> I've only once seen the RDF triple referred to as O-R-O (by  
>>> @danbri) i.e., Object-Relation-Object.
>>
>> IF you read the specs, however, it is abundantly clear that this is  
>> what an RDF triple means, viz. that a relation holds between two  
>> objects (I prefer "things", but....).
>
> Exactly!

? I thought you were arguing *against* this view ?

>
> So why: Subject-Predicate-Object  (SPO) everywhere re. RDF?

As I said, the terminology is used so as to make it easier to refer to  
the various parts of a triple. Yes, triples are ordered. The  
'linguistic' flavor of the SPO terminology is an unfortunate accident  
of history. In other forums, people talk of 'first' and 'second'  
'argument positions', which  for many people has the unpleasant  
metallic taste of mathematics. But its the same thing they are talking  
about.

But in any case, even if I agree that (in spite of the RDF spec),  
there is something intuitively significant about the idea of a  
'subject', I still don't see (to return to the thread topic) why a  
literal should not count as a perfectly good name for the subject of a  
description. Literals denote a rather limited range of things, to be  
sure: strings, numbers, dates, etc.. ; but these things are real  
things, and some of them play their small but nontrivial roles in our  
lives, so why should they be arbitrarily excluded from the universe of  
topics that can be the legitimate subjects of a description?

> O-R-O reflects what you've just described.

And what I just described is what the RDF spec says, in mind-numbing  
detail.

> Like many of the RDF oddities (playing out nicely in this thread),  
> you have an O-R-O but everyone talks about S-P-O.
>
> "Subject" has implicit meaning, it lends itself to describing  
> stuff.  If I recall, RDF stands for: Resource Description Framework.
>
> I guess "Description" also means nothing?

Not at all. RDF is indeed a language for describing, just like any  
other assertional logic. Descriptions are made up from assertions of  
relationships between things. Each RDF triple is a little assertion.

>>> In addition, I don't see Information and Data as being the same  
>>> thing. Information (as I know it) is about Data + Context.  Raw  
>>> Data (as I know it) is about: a unit of observation and deemed  
>>> worthy of description by its observer.  You have to give Names to  
>>> subject of a description. "23"^^xsd:number  isn't a Name.
>>
>> Why do you say this? It is certainly as much a name as, say,  
>> "Patrick J. Hayes". It is a well-formed string which denotes  
>> something, and its denotation is perfectly clear, in fact  
>> computable. So, it is a name. I challenge you to specify what you  
>> mean by "Name" in such a way that it excludes literals as names,  
>> other than by simply reiterating your bare claim that they are not.
>
> I mean an unambiguous Name for a Web of Semantically Linked Data.
>
> "Patrick J. Hayes" simply doesn't cut it as an unambiguous name  
> within the aforementioned Web.

"simply doesn't cut it" simply doesn't cut it as any kind of  
convincing argument. WHY does it not cut it? What is wrong with it as  
a name? It is certainly not ambiguous, as you seem to imply. As  
several people have pointed out, its hard to even imagine anything  
less ambiguous than an RDF literal. It contains a link (a URI) to the  
very specification which determines its own meaning. So, what other  
problems do you see with it as a name?

Pat


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Received on Friday, 2 July 2010 15:12:20 UTC

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