- From: David Wood <david@3roundstones.com>
- Date: Wed, 26 Sep 2012 13:25:06 -0400
- To: Lee Feigenbaum <lee@thefigtrees.net>
- Cc: W3C RDF WG <public-rdf-wg@w3.org>
- Message-Id: <F9521A3B-5034-45AD-9BD7-9910348A57F5@3roundstones.com>
Hi Lee, On Sep 26, 2012, at 12:41, Lee Feigenbaum <lee@thefigtrees.net> wrote: > On 9/26/2012 12:09 PM, David Wood wrote: >> * Some designs for carrying for metadata >> >> PROPOSED: In our dataset syntax, we'll say that metadata goes in the default graph >> +0.5, especially if it can be aligned with SPARQL service descriptions. >> >> > > What do existing systems do when importing a TriG file that contains data in the "default" graph? The Anzo store has no default graph, and therefore either throws an error or throws away any information in a TriG "default graph". Similarly, all TriG exported from Anzo does not have a default graph unless it's the serialization of a SPARQL RDF dataset (which by definition does have a default graph, of course). > > I bring this up because I brought up a related thread on public-sparql-dev recently: > > http://lists.w3.org/Archives/Public/public-sparql-dev/2012JulSep/0025.html > > In that thread, I asked: > > """ > Do all quad stores / named graph stores include a default graph? If the store that you develop or use does have a default graph, does that graph also have a name (URI)? > """ > > The answers were: > > Anzo -- no default graph (except ones assembled on the fly for querying). > OWLIM -- has a default graph with no URI > RDF::Query -- has a default graph with no URI > 4store & 5store -- default graph is a view on existing graphs (& therefore, I assume, doesn't exist for purposes of storing data) -- uses a "special" named graph for writing default data > TDB -- can either have an actual default graph or just use the default graph as a view onto the other named graphs > > Additionally, there was input from 3 implementers (SteveH, GregW, and Chime) that if they could re-implement their systems they would not include a default/unnamed graph. > > All of which is to say, I think there's a fair amount of evidence that the "default" or unnamed graph is not consistently used, and perhaps not widely used. We need to support it for compatibility, but I think it's a mistake to specify that anything important be put in that graph. I certainly agree that default graphs are used in inconsistent ways in existing systems and that the idea of a default graph in a system backing an HTTP or SPARQL endpoint is generally a bad idea. However, that is not what is being proposed. The proposal deals with syntax within a TriG-like document, specifically where metadata describing a graph goes. It does not suggest where that metadata would be stored in a system that parses such a document. It most certainly does not suggest that metadata in a default graph in a TriG-like document be put in the default graph in a system that parses such a document. It would be nice (IMO) if such systems had a standard place to describe the graphs that they ingest. That could happen via server-side implementations of SPARQL service descriptions or in some other way. Right now, it happens in a wide variety of ways, many of which are out-of-band to an underlying RDF store. Clearly that is an area ripe for standardization since almost everyone does it, but in non-standard ways. Regards, Dave > > Lee >
Received on Wednesday, 26 September 2012 17:25:43 UTC