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Re: ISSUE-105: Graph vs. dataset syntaxes

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 19 Dec 2012 12:34:16 +0000
Message-ID: <50D1B448.4020406@epimorphics.com>
To: public-rdf-wg@w3.org


On 19/12/12 10:25, Pierre-Antoine Champin wrote:
>
>
>
> On Thu, Dec 13, 2012 at 8:07 PM, Ivan Herman <ivan@w3.org
> <mailto:ivan@w3.org>> wrote:
>
>
>     On Dec 13, 2012, at 12:28 , Sandro Hawke wrote:
>
>      > On 12/13/2012 06:35 AM, Ivan Herman wrote:
>      >> I find this a sensible compromise...
>      >>
>      >
>      > Me too.   It seems to me basically what SPARQL does, and why it's
>     called the "default graph".
>      >
>      >> For Trig/Turtle this may not be formally relevant because,
>     afaik, Trig will have its own media type.
>
>
> Well, I think it *does* have an impact, especially because Trig has its
> own media type:
> if you GET something from the web, expecting a single graph, and getting
> some Trig (which you can tell immediately from the media-type),
> then this gives you guidance on how to handle it.

I think the issue is specific to JSON-LD which is trying to be a graph 
format and a dataset format, depending on whether there are any named 
graphs in a JSON-LD document.

Treating a graph as a dataset has an issue about reading it into another 
dataset e.g. record the source location.

Treating a JSON-LD document as a graph (because the app expects a 
graph), and, after some triples, gettign quads, is breaking the 
application assumption but conneg does not allow the app to specific in 
the JSON-LD case.

Some systems (most?) differentiate between quads and triples, for 
example, always using quads with the location as graph slot.

If you expect a graph and, after getting a lot of single graph data, you 
start getting quads/named graphs, your application has a problem.

But if the app is dataset aware always, recording source location is 
different.

	Andy
>
>
>      >> But, for example, if an extension of RDFa is defined some day
>     including facilities for graphs, this is probably an approach to follow.
>      >>
>      >
>      > If we agree with this resolution of ISSUE-105, I might suggest
>     this is new information and warrants briefly re-visiting this issue:
>      > RESOLVED: In TriG, triples of the dataset's default graph MUST be
>     surrounded by curly braces.
>      >
>      > http://www.w3.org/2011/rdf-wg/meeting/2012-10-17#resolution_2
>      >
>      > ... because with this approach it's much more natural to treat
>     the name-graph pairs as an ignorable addition to turtle.
>      >
>
>     +1
>
>
> I would tend to agree, but I think I remember someone (Steve?) arguing
> against it as they would like their parser to know from the start if
> they are dealing with a graph or a dataset, even in the absence of
> media-type... Which sounds like a reasonable use-case...
>
>    pa
>
>
>     Ivan
>
>      >      -- Sandro
>      >
>      >> Ivan
>      >>
>      >> On Dec 5, 2012, at 13:13 , Markus Lanthaler wrote:
>      >>
>      >>
>      >>> While JSON-LD is a dataset syntax we expect that in most cases
>     it will be
>      >>> used to express simple graphs. This might become problematic if
>     a consumer
>      >>> is unable to process datasets -- even in the case where the
>     dataset consists
>      >>> of only the default graph. In JSON-LD we resolved this issue by
>     specifying
>      >>> that a consumer expecting a graph, MUST ignore everything but
>     the default
>      >>> graph.
>      >>>
>      >>> This allows publishers to expose their graphs in, e.g., both
>     JSON-LD and
>      >>> Turtle. Summarized, the behavior of a consumer would be as follows:
>      >>>
>      >>> Exposed  |  Expected  |  behavior
>      >>> ---------+------------+-----------
>      >>> Data set |  graph     |  use default graph as graph, ignore rest
>      >>> Data set |  data set  |  exposed = expected
>      >>> Graph    |  data set  |  use graph as default graph in dataset
>      >>> Graph    |  graph     |  exposed = expected
>      >>>
>      >>>
>      >>> This might have consequences on how data should be modeled
>     (what should be
>      >>> put in the default graph and what in a named graph) but that's
>     beyond the
>      >>> scope of a syntax.
>      >>>
>      >>> I would therefore like to propose to standardize this behavior
>     for all RDF
>      >>> data set syntaxes.
>      >>>
>      >>>
>      >>> Regards,
>      >>> Markus
>      >>>
>      >>>
>      >>> --
>      >>> Markus Lanthaler
>      >>> @markuslanthaler
>      >>>
>      >>>
>      >>>
>      >>
>      >> ----
>      >> Ivan Herman, W3C Semantic Web Activity Lead
>      >> Home:
>      >> http://www.w3.org/People/Ivan/
>      >>
>      >> mobile: +31-641044153 <tel:%2B31-641044153>
>      >> 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 <tel:%2B31-641044153>
>     FOAF: http://www.ivan-herman.net/foaf.rdf
>
>
>
>
>
>
Received on Wednesday, 19 December 2012 12:34:46 GMT

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