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Re: Subjects as Literals

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 30 Jun 2010 21:30:14 -0500
Cc: David Booth <david@dbooth.org>, nathan@webr3.org, Toby Inkster <tai@g5n.co.uk>, Dan Brickley <danbri@danbri.org>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <2D692D0C-0D6D-426D-AFA8-1459D4A1F6ED@ihmc.us>
To: Kingsley Idehen <kidehen@openlinksw.com>

On Jun 30, 2010, at 2:31 PM, Kingsley Idehen wrote:

> David Booth wrote:
>> On Wed, 2010-06-30 at 14:30 -0400, Kingsley Idehen wrote:
>>
>>> Nathan wrote:
>>>
>>>> Pat Hayes wrote:
>>>>
>> [ . . . ]
>>
>>>> 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.
>>>
>>> If you are in a situation where you can't or don't want to mint an  
>>> HTTP based Name, simply use a URN, it does the job.
>>>
>>
>> Can you explain *why* you think literals should not be permitted as
>> subjects?  The rationale you have given above sounds like it is  
>> saying
>> that literals should not be subjects because RDF does not permit
>> literals to be subjects.
>> IMHO, RDF should allow "anyone to say anything about anything" -- not
>> "anyone to say anything about anything . . . except a literal".
>> However, if you see some specific harm in permitting statements about
>> literals, please tell us what that harm would be.
>>
>>
>>
>>
> Harm isn't of the "breaks anything variety". It just adds ambiguity  
> to the process of producing structured descriptions within Web realm.
>
> I could flip this around and ask: what makes a pure URN or other  
> identification schemes (that may or may not resolve to anything)  
> problematic?

1. There are infinitely many numbers.
2. There is no systematic convention for specifying a URN for a given  
number; whereas there are such conventions, established, standardized  
and widely implemented, for (literals using) XSD datatypes.
3. The datatyping mechanism in RDF was created for exactly this  
purpose. To refuse to use it and insist upon developing an alternative  
(especially one which would require an infinite amount of work) seems  
therefore to be obtuse.

> I am of the assumption that we are seeking globally unambiguous  
> names (which may or may not resolve) re. Web of Linked Data aspect  
> of Semantic Web continuum.

Quite. A typed literal is a globally unambiguous name for the datatype  
value it denotes.

> RDBMS engines support literal identifiers

That is a different topic. Nobody is suggesting using literals to  
identify non-literal values. In RDF, the interpretation of a literal  
is *fixed* by the RDF specs.

Pat Hayes


> , and the consequences are:
>
> 1. Distributed RDBMS tedium -- due to object ambiguity across  
> Qualifier/Schema/Database, Owner, and actual Object Name (Tables,  
> Views, Procedures) names
> 2. Security problems -- users are Identified using literals instead  
> of proper identifiers (as demonstrated by FOAF+SSL [3]  WebIDs you  
> can provide blockers to socially engineered RDBMS vulnerability via  
> verifiable identity + data access policies).
>
>
> Links:
>
> 1. http://en.wikipedia.org/wiki/Identifier
> 2. http://en.wikipedia.org/wiki/Unique_identifier
> 3. http://esw.w3.org/Foaf%2Bssl
>
> -- 
>
> Regards,
>
> Kingsley Idehen	      President & CEO OpenLink Software     Web: http://www.openlinksw.com
> Weblog: http://www.openlinksw.com/blog/~kidehen
> Twitter/Identi.ca: kidehen
>
>
>
>
>
>

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Received on Thursday, 1 July 2010 03:02:18 UTC

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