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Re: Well Behaved RDF - Taming Blank Nodes, etc.

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Sat, 15 Dec 2012 17:39:41 +0000
Message-ID: <50CCB5DD.1060005@epimorphics.com>
To: semantic-web@w3.org


On 14/12/12 21:06, Ivan Herman wrote:
>
> On Dec 14, 2012, at 02:45 , Ivan Shmakov wrote:
>
>>>>>>> Ivan Herman <ivan@w3.org> writes:
>>>>>>> On Dec 13, 2012, at 12:42 , David Booth wrote:
>>
>> […]
>>
>>>>> The restriction of "no labels" is not just about "no cycles" — it's
>>>>> things that are not tree-like:
>>
>>>>> :x1 :p _:a .
>>>>> :x2 :q _:a .
>>
>>>> Yes, excellent example.  I explained to Pat in
>>>> http://lists.w3.org/Archives/Public/semantic-web/2012Dec/0040.html
>>>> why I chose the "no labels" restriction instead, but I'm open to
>>>> considering either.
>>
>>> I think it would still be better to explain these things in a syntax
>>> independent way.  After all, I may want to use JSON-LD or RDFa...
>>
>>> Distilling the various mails and concentrating on bnodes only, what
>>> seems to be the pattern is
>>
>>> - bnodes can appear in at most one triple as an object
>>
>> 	AIUI, this restriction was added merely to allow for a simpler
>> 	WB-RDF definition.  It wouldn't be necessary should Turtle have
>> 	included a “inverse property” syntax.  (Which I doubt it'll
>> 	acquire in a foreseeable future.)
>>
>
> You are right, it will not... The current Turtle will go to CR soon (ie, early next year)

(hypothetically speaking)

It depends on what is the "subject" :-)

If inverse properties are just surface syntax, it would be appropriate 
to use language like to talk inverse properties like:

object ^property subject

so the subject is still "the subject" of a triple.

	Andy

>
>
>> 	However, as I've noted earlier, when this restriction is in
>> 	effect, it's simple to assign (semi-)unique identifiers to all
>> 	the blank nodes, based solely on their relation to the other
>> 	nodes.  (Provided that the next criterion is also met.)
>>
>>> - there can be no cycle in the graphs involving bnodes
>>
>> 	I believe that the point was that there'd be no cycles
>> 	consisting /exclusively/ of bnodes.
>
> Right, I was sloppy. See my reply to David...
>
> Ivan
>
>
>>
>>> Would that suffice as a more formal definition?
>>
>> --
>> FSF associate member #7257
>>
>>
>
>
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> FOAF: http://www.ivan-herman.net/foaf.rdf
>
>
>
>
>
Received on Saturday, 15 December 2012 17:40:09 UTC

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