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Re: Graph store protocol editor's draft updated

From: Gregory Williams <greg@evilfunhouse.com>
Date: Thu, 16 Feb 2012 20:55:21 -0500
Cc: Chimezie Ogbuji <chimezie@gmail.com>, SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <8DC6BF8A-86D1-4974-928E-140868438C88@evilfunhouse.com>
To: Sandro Hawke <sandro@w3.org>
On Feb 14, 2012, at 10:56 AM, Sandro Hawke wrote:

> If for some reason, you all still are not convinced, the other option:
> 
>>> I really liked indirect IRIs, and I think the Provenance WG was counting
>>> on them, since they let folks use an IRI to talk about a graph in
>>> SPARQL-land.  But now they don't do that any more.
>>> 
>>> I'd be okay with either:
>>> (1) putting 5.8 back
>> 
>> Note, Greg is not okay with this.
> 
> Looking more closely, it's not 5.8 that I want back, it's this sentence:
> 
>        Within a service description document for an implementation of
>        this protocol, the object of an sd:defaultDataset statement is
>        understood to be the identifier of the Graph Store
> 
> and the accompanying illustration in section 5.5, showing how sd:default
> Dataset is used (but modified to be clear it's the endpoint, not the GSP
> service, which no longer exists).   To clarify, I mean this to be
> talking about a SPARQL SD, not some kind of graphstore SD.  
> 
> As far as I can tell this is conceptually redundant.  I believe the WG
> agrees that the object of an sd:defaultDataset statement *is* understood
> to be the identifier of the Graph Store, it's just... we don't actually
> say that in any specs any more.

I don't think I'd agreed with this statement. The default dataset needn't be the same thing as the underlying graph store; it can be *anything*. The default dataset might be entirely empty. Or it might be the entire graph store. Or it might have a default graph that is some weird aggregation of graphs from the underlying graphstore. This is part of the reason why we have the sd:availableGraphs property: to be able to indicate which graphs are made available from the underlying graph store when it comes to non-default dataset construction.


Somewhat relatedly, I went to try to find text in the GSP document about support for default graphs. I was surprised that I couldn't find any real statement that a graph store actually supports a default graph. The Update document has a good definition that lays this out, and while there's a citation to the Update document after the GSP's definition of Graph Store, that definition doesn't really address this: "Graph Store - A mutable repository of RDF graphs managed by one or more services."

The definition of "RDF graph content" in GSP kind of indicates that a default graph can be identified. Aside from that, though, it's not until section 4.2 that there's text about how a default graph can be identified, implicitly suggesting that a graph store does have a default graph. Having some explicit text about this early on in the doc might be useful.

.greg
Received on Friday, 17 February 2012 01:55:47 GMT

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