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Re: Comment on RDFa 1.1 Core: Profiles, term mappings, and URIs as literals (ISSUE-39)

From: Richard Cyganiak <richard.cyganiak@deri.org>
Date: Thu, 12 Aug 2010 13:59:30 +0100
Cc: Ivan Herman <ivan@w3.org>, public-rdfa-wg@w3.org
Message-Id: <85C486C1-C4B7-4E4C-9E8E-076FABD249D0@deri.org>
To: Mark Birbeck <mark.birbeck@webbackplane.com>
Mark,

You are arguing that something that can obviously be done in practice  
actually is completely impossible in theory.

I will now pay the RDF Tax and waste an hour of my life to show you  
that what is possible in practice, is of course possible in theory as  
well, you just need to do some mental gymnastics to get RDF Semantics  
to play along.

On 12 Aug 2010, at 11:55, Mark Birbeck wrote:
> if I make a statement about
> <http://purl.org/dc/terms/> I am making statements about the /entity/
> this URI refers to. The URI is the name for the entity, and it's not
> possible to say anything about the /name/ in RDF (i.e., about the
> URI).
>
> For this reason, the following technique is a non-starter:
>
>  <http://xmlns.com/foaf/0.1/name> rdfa:term "blabla" .
>
> The desire is to make a statement about a string of text that can be
> substituted during RDFa parsing, but this statement doesn't do that;
> instead it is making a statement about the *entity represented by the
> URI*. No matter which way we twist and turn, it is not possible to do
> anything otherwise in RDF.

I can parse the RDF statement above using my library of choice, and  
run the following SPARQL query over it:

SELECT ?uri WHERE { ?uri rdfa:term "blabla" }

The answer will be <http://xmlns.com/foaf/0.1/name>. And this is all  
that is needed, end of story.

Now your argument is that the library didn't return a string but a  
URI, which is just a reference to some entity in the world. And hence  
I am not allowed to do stringy things with the returned URI. While the  
first part is true, I really don't get where you get that second part  
from.

> * in RDF you can't saying anything about the lexical form of a URI;

Where in RDF Semantics does it say please that the universe excludes  
the URIs of things? I demand a quote. If there's no such restriction  
in the spec, then I can use RDF to say things about URIs.

Example. In the world of RDF Semantics, URIs are identifiers for  
entities. So let X be the relationship that holds between an entity  
and the number of characters of a URI that identifies this entity.  
Furthermore, let foo:uriLength be an identifier for this relationship X.

Now this is a trivially true statement:

<http://xmlns.com/foaf/0.1/name> foo:uriLength 30 .

While we have no evidence for the following statements (and hence can  
conclude they are false under closed-world reasoning):

<http://xmlns.com/foaf/0.1/name> foo:uriLength 29 .
<http://xmlns.com/foaf/0.1/name> foo:uriLength 31 .

Look, I'm making statements about the lexical form of a URI.

> * any properties we add to a URI concern the entity that URI
> represents, and not the string of characters itself;

That is correct, but consistent with my proposed definition of  
rdfa:term. In RDF Semantics language, rdfa:term identifies the binary  
relationship that holds between an entity and a short form for the URI  
of that entity.

Best,
Richard



> * I think you should stick to your pedantry, Ivan! ;)
>
> Regards,
>
> Mark
>
> --
> Mark Birbeck, webBackplane
>
> mark.birbeck@webBackplane.com
>
> http://webBackplane.com/mark-birbeck
>
> webBackplane is a trading name of Backplane Ltd. (company number
> 05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
> London, EC2A 4RR)

-- 
Linked Data Technologist  Linked Data Research Centre
Digital Enterprise Research Institute (DERI), NUI Galway, Ireland
http://linkeddata.deri.ie/
skype:richard.cyganiak
tel:+353-91-49-5711
Received on Thursday, 12 August 2010 13:00:06 GMT

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