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Re: Three solution designs to the first three Graphs use cases

From: David Wood <david@3roundstones.com>
Date: Wed, 1 Feb 2012 10:35:32 -0500
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, public-rdf-wg@w3.org
Message-Id: <BE2DF398-D3CC-4685-9EF5-D945931E1027@3roundstones.com>
To: Alex Hall <alexhall@revelytix.com>
On Feb 1, 2012, at 10:30, Alex Hall wrote:

> On Wed, Feb 1, 2012 at 8:58 AM, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:
> 
> 
> On 01/02/12 13:40, David Wood wrote:
> >>>    <s>   <p>   {<a>   <b>   <c>   }
> >>>
> >>>  you mint an identifier (<g1>   ) then store these quads:
> >>>
> >>>    <s>   <p>   <g1>   DEFAULT
> >>>    <a>   <b>   <c>   <g1>
> >>
> >>
> >>  For what it is worth, this is what Mulgara does.
> 
> Actually, this is incorrect. Mulgara will never mint a new graph identifier for you. Mulgara doesn't even support any multi-graph formats, since its developers have been busy with their day jobs :-)


Alex is correct that Mulgara doesn't support graph literals, nor automatically generate new graphs.  However, it does allow for the creation of new graphs (on command) and the storage of the graph relationships as the last element of the quads.

Regards,
Dave


> 
> Mulgara only supports single-graph formats (RDF/XML, Turtle, RDFa) and you must explicitly tell Mulgara the URI of the graph into which you are loading a document. There's no SPARQL 1.1 support (see "day jobs" above) so you can't insert into the default graph.
>  
> >
> >  David,
> >
> >  Does Mulgara claim to support graph literals?
> Mulgara supports what it calls named graphs.  In fact, you*can't*  query Mulgara (or its predecessors) without querying a particular graph.  Our original query language (TQL) forced you to name a graph; the SPARQL implementation defaults to the default graph as configured, I believe.  Each quad is indexed with its graph membership.
> 
> 
> There are some "special" graphs in Mulgara, especially the "system" graph that stores triples about all the graphs that the system holds.  They are exposed and queryable.
> 
> Right, but named graphs and graph literals are very different. It's true that one possible implementation of graph literals is to use specially-minted internal graph ID's, but Mulgara doesn't do that.
>  
> 
> >
> >  What does
> >
> >  SELECT ?o {<s>  <p>  ?o }
> >
> >  return?
> If you queried the system graph thusly you would get the list of graph URIs held by that Mulgara instance.
> 
> Query the configured default graph.
> 
> Does ?o return  {<a>   <b>   <c>   } or <g1> or something else?
> 
> (By the way - is the data syntax for graph literals understood by Mulgara documented anywhere?)
> 
> Just to be clear, Mulgara claims no support for graph literals.
> 
> -Alex
> 
Received on Wednesday, 1 February 2012 15:36:01 UTC

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