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Re: New Proposal (6.1) for GRAPHS

From: Ivan Herman <ivan@w3.org>
Date: Mon, 2 Apr 2012 18:13:33 +0200
Cc: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, public-rdf-wg <public-rdf-wg@w3.org>
Message-Id: <8084A732-8E92-4F7B-BC10-455EA410009B@w3.org>
To: Sandro Hawke <sandro@w3.org>

On Apr 2, 2012, at 17:52 , Sandro Hawke wrote:

> On Mon, 2012-04-02 at 17:19 +0200, Ivan Herman wrote:
[skip]
> 
>> As for implementations: today, an implementation probably has the notion of a triple, which may have s,p,o, which can be of class... well, you know that. Those classes, including all the code that rely on those classes, will have to be extended to allow for a 4th type of thing, otherwise they may throw exceptions, go wrong, blow up, etc. I am not sure I can foresee all the consequences.
>> 
>> (I know a bit RDFLib from inside. It does have the notion of a Graph, of course, which can even have an associated label. But all the code that, say, retrieves triples from a graph store rely on the fact that any resource has to be Literal, URIRef, or BNode, to use the RDFLib terminology. Those methods are not necessarily prepared for the possibility of having a Graph at places.)
> 
> No, in this plan, normal RDF is unchanged.   Just because the object of
> a triple can *semantically* refer to an RDF Graph does not mean the RDF
> Abstract Syntax has to be extended to help it do so.   The object of a
> triple can *semantically* refer to a person, but there's no special node
> type in the RDF Abstract Syntax to support that -- people have to be
> identified by URIRef and/or BNodes.   RDF Graphs, as I imagine it, are
> like that, too.   In Plain-Old-RDF (as found in RDF/XML, Turtle, the
> default graph of a TriG document, or any of the named graphs in a TriG
> document) the Graphs are referred by URIRefs or BNodes.

So we open up the can of worm of of HTTPRange-14?

<a> <b> <http://www.ivan-herman.net/foaf#me> .

uses (to use the HTTPRange-14 terminology) a URI to refer to a non-informational resource referring to me (I may not use the right words here). In terms of RDF, <http://www.ivan-herman.net/foaf#me> is 'just' a URI, nothing special.

In

<a> <b> { <p> <q> <r> } .

what is the equivalent of <http://www.ivan-herman.net/foaf#me> ? Do we have some sort of an ad-hoc URI to refer to the non-informational resource that is the graph? 

And... I still fail to understand what it buys us to use a predicate for what we want to achieve for named graphs here? Why do we want to push this particular thing into the RDF Concept/Semantics?

Ivan

P.S. *Personally* the way I would describe that stuff above is to use graph literals. That is, for me, a clean way of doing that: the datatype definition in RDF gives me quite some leeway to define the value space, so it could be the set of RDF graphs as a mathematical notion. That is clean, conceptually and we would have no problem. But we saw quite some pushbacks, based on implementations, on going down that particular road, so that is not a possibility.






> 
> Maybe there's a use case we can talk through, even implement in Python,
> to make this more clear....    Maybe "keeping inferred triples
> separate", or some version of the endorsement case, or some provenance
> example?
> 
>    -- Sandro
> 
>> And... what does it buy us? There is nothing that forces us to go down that route. The type of a Graph 'label' can be defined outside of the formal RDF Semantics and concepts, and things work just as well (I know Pat will shoot me down, though:-)
>> 
>> Ivan
>> 
>>> 
>>>   -- Sandro
>>> 
>>>> Personally, I would keep away from that: I am not sure we can do it in time, I am not sure it is consensus ready for a standard. The labels in a (l,G) pair are URI refs (or BNodes), ie, they can be typed to any RDF graphs; but I think the exact semantics of what that means should be defined _outside_ of the formal RDF semantics (essentially in English prose).
>>>> 
>>>> Maybe RDF 2.0 can provide a mathematically precise semantics. Maybe we can publish a note for the direction such a recommendation might take. But I am not sure we can go beyond that.
>>>> 
>>>> (Yes, I may be in my pessimistic mood.)
>>>> 
>>>> Ivan
>>>> 
>>>> 
>>>> 
>>>>> 
>>>>> -- Sandro
>>>>>> 
>>>>>> peter
>>>>>> 
>>>>>> 
>>>>>> On 03/27/2012 10:23 PM, Sandro Hawke wrote:
>>>>>>> I've written up design 6 (originally suggested by Andy) in more
>>>>>>> detail.  I've called in 6.1 since I've change/added a few details that
>>>>>>> Andy might not agree with.  Eric has started writing up how the use
>>>>>>> cases are addressed by this proposal.
>>>>>>> 
>>>>>>> This proposal addresses all 15 of our old open issues concerning graphs.
>>>>>>> (I'm sure it will have its own issues, though.)
>>>>>>> 
>>>>>>> The basic idea is to use trig syntax, and to support the different
>>>>>>> desired relationships between labels and their graphs via class
>>>>>>> information on the labels.  In particular, according to this proposal,
>>>>>>> in this trig document:
>>>>>>> 
>>>>>>>  <u1>  {<a>  <b>  <c>  }
>>>>>>> 
>>>>>>> ... we only know that<u1>  is some kind of label for the RDF Graph<a>
>>>>>>> <b>  <c>, like today.  However, in his trig document:
>>>>>>> 
>>>>>>>  {<u2>  a rdf:Graph }
>>>>>>>  <u2>  {<a>  <b>  <c>  }
>>>>>>> 
>>>>>>> we know that<u2>  is an rdf:Graph and, what's more, we know that<u2>
>>>>>>> actually is the RDF Graph {<a>  <b>  <c>  }.  That is, in this case, we
>>>>>>> know that URL "u2" is a name we can use in RDF to refer to that g-snap.
>>>>>>> 
>>>>>>> Details are here: http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1
>>>>>>> 
>>>>>>> That page includes answers to all the current GRAPHS issues, including
>>>>>>> ISSUE-5, ISSUE-14, etc.
>>>>>>> 
>>>>>>> Eric has started going through Why Graphs and adding the examples as
>>>>>>> addressed by Proposal 6.1:
>>>>>>> http://www.w3.org/2011/rdf-wg/wiki/Why_Graphs_6.1
>>>>>>> 
>>>>>>>    -- Sandro (with Eric nearby)
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>> 
>>>> 
>>>> ----
>>>> 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
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>>> 
>> 
>> 
>> ----
>> 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
>> 
>> 
>> 
>> 
>> 
> 
> 


----
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 Monday, 2 April 2012 16:12:18 GMT

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