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Re: Understanding 'chaining'

From: Ivan Herman <ivan@w3.org>
Date: Thu, 29 Nov 2007 15:45:19 +0100
Message-ID: <474ED07F.5030904@w3.org>
To: Mark Birbeck <mark.birbeck@x-port.net>
Cc: Ben Adida <ben@adida.net>, RDFa <public-rdf-in-xhtml-tf@w3.org>
A short reply on a long mail...

I will read it again in more details later and this may generate another
reply but it seems that you pretty much misunderstood what I wrote. It
is probably my fault. However:

Mark Birbeck wrote:
[snip]
> 
> 
>> What made me tip the balance is one of Ben's example, namely:
>>
>> <div about="#me" rel="foaf:knows">
>>   <span property="foaf:firstname" content="Ivan"></span>
>>   <span property="foaf:lastname" content="Herman"></span>
>> </div>
>>
>> yielding (in his mail)
>>
>> <#me> foaf:knows [foaf:firstname "Ivan" ; foaf:lastname "Herman"] .
>>
>> I am sorry, but I find it highly inconsistent.
> 
> With respect Ivan, it's a little late in the day to be saying this.
> This formulation has been agreed on for a long time now. This is Ben's
> version of chaining, and as I've said before, it is incredibly close
> to our 'old' version of chaining...but not quite. But either way,
> we've been using it for a long time now.
> 

With respect Mark, I know:-) Give me some credit, please...

What I found inconsistent (and I should have written down more clearly)
is the contrast of what stands there with

<div about="#me" rel="foaf:knows">
  <span about="#a" property="foaf:firstname" content="Ivan"></span>
  <span about="#b" property="foaf:lastname" content="Herman"></span>
</div>

which yields

<#me> foaf:knows <#a>, <#b>.
<#a> foaf:firstname "Ivan".
<#b> foaf:lastname "Herman".

Ie, that the triples generated by the two <span>-s within the <div> are
sometimes 'merged' to refer to the same subject, and sometimes they are
not. _This_ is the inconsistency (actually, also referred to by Ben)
that I do not like. (Am I allowed to use this term?).


[snip]
>> As far as I am concerned, the natural
>> interpretation of the code above would be
>>
>> <#me> foaf:knows [foaf:firstname "Ivan"], [foaf:lastname "Herman"] .
>>
>> Which, I presume, is really not what we want.
> 

'Natural' interpretation v.a.v. the case when we have two <span>-s with
@about values like above.

>> The inconsistency becomes
>> even more appearent for me if I write
>>
>> <div about="#me" rel="foaf:knows">
>>   <span property="foaf:firstname" content="Ivan"></span>
>>   <span property="foaf:lastname" content="Herman"></span>
>>   <span about="#mark" property="foaf:lastname" content="Birbeck"></span>
>> </div>
>>
>> That would yield, in the new model:
>>
>> <#me> foaf:knows
>>         [foaf:firstname "Ivan" ; foaf:lastname "Herman"], <#mark> .
>> <#mark> foaf:lastname "Birbeck".
> 
> I don't know what to say here, Ivan...this set of triples is also
> yielded by the current model. See section 6.2.2.4 of the *current*
> draft of the RDFa syntax document, for example.
> 

Mark, that is not true. In the current model, the triple

<#me> foaf:knows <#mark> .

is _not_ generated!

In the current model the presence of an @about means a 'cut', so to say,
form the triples and the resources up in the tree.
> 
> 
> OTHERWISE WE GET MEANINGLESS TRIPLES
> 
> As I said in another post, if we don't take the 'defer' approach, then
> we get meaningless triples from mark-up like this:
> 
>  <div about="A" rel="p:p1" />
> 
> Generating a triple here goes against the whole point of bnodes!
> 
> But there is worse; in this situation:
> 
>   <div about="#me" rel="foaf:knows">
>     <span about="#mark" property="foaf:lastname" content="Birbeck"></span>
>   </div>
> 
> we will get a meaningless triple, as follows:
> 
>   <#me> foaf:knows _:div0 .
>   <#mark> foaf:lastname "Birbeck" .
> 

That is correct.:-(


Ivan

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Thursday, 29 November 2007 14:45:23 GMT

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