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

From: Alex Hall <alexhall@revelytix.com>
Date: Wed, 1 Feb 2012 10:30:54 -0500
Message-ID: <CAFq2biyMp6yA26JEygGoJRd5YRT+-U9yO-_WBn0uVCHKYEGguw@mail.gmail.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
Cc: public-rdf-wg@w3.org
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 :-)

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 15:31:53 UTC

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