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

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)


> 	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