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Re: GET on a graph store URI / Graph Store HTTP Protocol

From: Gregory Williams <greg@evilfunhouse.com>
Date: Sat, 17 Dec 2011 00:44:08 -0500
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, sparql Working Group <public-rdf-dawg@w3.org>
Message-Id: <69968AD9-2366-4BC1-BBC0-2DE7EE632037@evilfunhouse.com>
To: Sandro Hawke <sandro@w3.org>
On Dec 17, 2011, at 12:05 AM, Sandro Hawke wrote:

>> 2/ Could we allow GET on a graph store URI return quads?
> 
> I think so, yes.
> 
> 
> There are two very different things people might reasonably want to do
> here: get a dump of the dataset, and get a dump of the URLs used to
> access the graphs in the dataset.   I think at some point both need to
> be supported, but it looks like we have that with SD.
> 
> As I understand it, given a SPARQL endpoint with address E:
> 
>   GET E
>   ... returns the Service Description (SD)
> 
>   Query SD for { ?S sd:endpoint <E>; sd:defaultDataset ?D }
> 
>   GET ?D
>   ... should return a TriG/N-Quads serialization of the given dataset;

We agree that this is at odds with the GSHP text as it currently stands, right?

>     (but doesn't with the current GSHP)
>   PUT ?D <somedata> 
>   ... should replace the dataset

I'm not sure we've ever really nailed down whether this should work. ?D here is the resource for the default dataset, which I wouldn't assume is necessarily the same thing as the graph store. For that matter, ?D might not even be a dereferenceable IRI.

>        Query SD for { ?D sd:namedGraph/sd:name ?N } and ?N comes back
>        with each of the graph URLs.
> 
> I don't suppose we can require SPARQL 1.1 endpoints to answer queries
> about their own SD, maybe using FROM their own endpoint address...?
> Otherwise, what, you need your own SPARQL server before you can start to
> poke at someone else's?

We had early discussions about this while deciding how a service description was to be made available. I think it would be nice for systems to be able to do this (you get it for free on systems that dereference FROM IRIs), but I wouldn't want to mandate it. Also, I don't think you need a full SPARQL implementation to benefit from a service description. A simple triple store would allow you to access the data you've discussed above with simple triple pattern matching and a couple of loops.

.greg
Received on Saturday, 17 December 2011 05:44:34 GMT

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