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Re: Making progress on graphs

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 15 May 2012 13:49:05 +0100
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, public-rdf-wg@w3.org
Message-Id: <935A3C86-11F3-4363-BBB7-6124A4095CD2@cyganiak.de>
To: Sandro Hawke <sandro@w3.org>
Sandro,

On 15 May 2012, at 12:58, Sandro Hawke wrote:
> If we followed your proposal and made datasets (with possibly-empty
> named graphs) our basic unit, then people would no longer be able to use
> quad-stores or quad syntaxes (like N-Quads) while conforming to our
> specs.

That is nonsense.

Quad stores already use RDF datasets with possibly empty named graphs as their basic unit. That is how SPARQL is defined. The Update spec simply allows them to drop empty graphs upon insert.

N-Quads cannot serialize all RDF datasets, just like RDF/XML cannot serialize all RDF graphs. The existing N-Quads spec explicitly refers to serialization of RDF datasets as one application of N-Quads.

There are already several quad-based RDF stores (Virtuoso, Sesame, 4store) that use TriG as an exchange syntax. TriG supports empty graphs. They ignore the empty graphs. After all, an RDF store MAY drop empty graphs — that's already in the SPARQL Update spec.

ISSUE-22 is: “Does multigraph syntax need to support empty graphs?”

My proposed answer to that is: “Yes, the multigraph abstract syntax that we specify needs to have support for empty graphs.”

Your own rdf-spaces proposal supports empty graphs, so it actually agrees with the proposal.

Best,
Richard
Received on Tuesday, 15 May 2012 12:49:56 GMT

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