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Re: The Ordered List Ontology

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 1 Jul 2010 01:53:52 -0500
Cc: Dan Brickley <danbri@danbri.org>, Toby Inkster <tai@g5n.co.uk>, Graham Klyne <GK@ninebynine.net>, Bob Ferris <zazi@elbklang.net>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <6654A59E-B7B2-4981-9479-5BB35F22055D@ihmc.us>
To: Harry Halpin <hhalpin@ibiblio.org>

On Jun 30, 2010, at 6:24 PM, Harry Halpin wrote:

> On Wed, Jun 30, 2010 at 8:17 PM, Pat Hayes <phayes@ihmc.us> wrote:
>>
>> On Jun 30, 2010, at 1:15 PM, Dan Brickley wrote:
>>
>>> On Wed, Jun 30, 2010 at 6:34 PM, Pat Hayes <phayes@ihmc.us> 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.
>>>
>>> Yes.
>>>
>>> So this is a point that probably needs careful presentation to new
>>> users of this technology. Educating people that they shouldn't  
>>> believe
>>> any random RDF they find in the Web, ... now that is pretty easy.
>>> Still needs doing, but it shadows real world intuitions pretty well.
>>>
>>> If in real life you think the Daily Mail is full of nonsense, then  
>>> it
>>> isn't a huge leap to treat RDFized representations of their claims
>>> with similar skepticism (eg. see
>>> http://data.totl.net/cancer_causes.rdf for a great list of Things  
>>> The
>>> Daily Mail Say Might Cause Cancer).
>>>
>>> *However* it is going to be tough to persuade developers to treat a
>>> basic data structure like List in the same way.
>>
>> Sure.  But what they need to grok is that RDF does not have ANY data
>> structures in it (except maybe triples). It describes data  
>> structures, just
>> like it describes everything else. It does not PROVIDE data  
>> structures.
>> Maybe it should - make the case! - but then it will need to change  
>> rather
>> drastically in its very foundation. Triples describing lists are  
>> not the
>> same as triples-plus-lists.
>
> The issue is here that RDF started as a metadata format to "describe"
> data I believe, and at this point with the Linked Data is now being
> transformed into a generic language *for* data, period.

Is this really the case? I wasn't part of the very first RDF  
initiative, but ever since I've been involved with it, its purpose was  
pretty explicitly supposed to be for representing information - call  
it data if you like - rather than anything "meta". I've never read  
anything that suggest that RDF is supposed to be describing data. It  
is supposed to be describing the world.

>  The lack of
> lists (and hashes, and other things programmers are used to dealing
> with) in a reasonable (read "non-XML") syntax is one of the primary
> reasons the developer community has moved towards JSON.

Well, Im all for JSON, but JSON is a programming language, not a  
language for stating facts in. If anything, JSON would be the  
metalanguage here, being used to do things to RDF syntax, I presume.

>
> Now, the question is "Would it be possible to provide a JSON-like
> number of data-structures in RDF, and what would this do to its
> semantics?" Pat?

Well, it would be up to whoever was designing this RDF/JSON to say  
what the logical semantics of these data structures was. The problem  
is that as soon as you say what it is, these structures have had their  
meaning specified so they aren't 'free' to be used by programmers to,  
well, program with. Or, on the other hand, if you let the programmers  
have free rein, then they can build things that violate the semantics,  
eg suppose we let them write code that tweaks RDF triples into quads,  
say: now what do the quads mean?

>
> Given that programming langauge semantics define these things all the
> time and it's pretty standard, I imagine its possible.

PL semantics just specifies what the programs do. Its a different kind  
of semantic theory. Putting it all together requires one to decide how  
the programming processes relate to the assertions of facts.

> But it might
> make life hard for the principles that RDF was founded upon, i.e. the
> sort of "open world" flavor of it all.

Maybe. I think its more a problem of keeping everything kind of  
rational. I mean, folk are bothered by a few knotted lists, but  
allowing processes to tweak the logical syntax in arbitrary ways is a  
far worse nightmare.

Pat

>
> Thus, I imagine it's a trade-off, like most good things in life :)
>
>>
>> Pat
>>
>>> Lists are the kinds of
>>> thing we expect to be communicated perfectly or to get some low- 
>>> level
>>> error. A lot of developers will write RDF-consuming code that won't
>>> anticipate errors. Hopefully supporting software libraries can take
>>> some of the strain here...
>>>
>>> cheers,
>>>
>>> Dan
>>>
>>>
>>
>> ------------------------------------------------------------
>> IHMC                                     (850)434 8903 or (650)494  
>> 3973
>> 40 South Alcaniz St.           (850)202 4416   office
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>>
>>
>>
>>
>>
>>
>>
>
>

------------------------------------------------------------
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 July 2010 06:55:22 UTC

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