Re: why I don't like default graphs in the DATASET proposal

On 2011-09-29, at 15:42, Pierre-Antoine Champin wrote:


> A such, I consider the default graph to be a *property of the SPARQL
> engine* used to query the data, rather than a property of the data itself.

I'm tempted to agree.

> The fact that the SPARQL rec had to define all together the data
> structure and the querying process can explain that they ended up with
> the dataset proposal as it is.
> I agree with Richard that we should integrate a proposal that has
> already been widely implemented and tested, rather than reinventing the
> wheel. However, keeping default graphs looks like keeping the bath water
> with the baby...
> I would prefer, in a nutshell, if the proposal was to :
> * define an RDF DATASET as a set of named graphs (uri, graph) -- i.e.
> remove the default graph;
> * explain that a SPARQL DATASET, used by a particular SPARQL engine, is
> an RDF DATASET where one of the named graphs is also considered the
> default graph in order to allow for shorter queries.
> I know that SPARQL does not require that the default graph is *also*
> present as a named graph (though it does not forbid it), so the
> statement above is slightly more constraining than what SPARQL specifies.
> So here are a few questions to SPARQL implementers: is it more frequent
> that the default graph also has a URI, or that it doesn't? Would it be
> hard to ensure that it has one? Would that break something in existing
> applications?

In both 4store and 5store the normal situation is that the default graph is the RDF Union of all named graphs, but it may be configured to be the union of any set of named graphs in the store. There is no option to have a default graph containing triples that aren't in a named graph.

We have found that these options map well to usecases we've encountered, but I'm aware there are others that it doesn't meet.

- Steve

Steve Harris, CTO, Garlik Limited
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Received on Friday, 30 September 2011 10:31:03 UTC