W3C home > Mailing lists > Public > public-lod@w3.org > February 2012

Re: Metadata about single triples

From: Barry Norton <barry.norton@ontotext.com>
Date: Wed, 22 Feb 2012 17:30:01 +0000
Message-ID: <4F452619.4060305@ontotext.com>
To: public-lod@w3.org
On 22/02/2012 17:21, Bob Ferris wrote:
> [...] Named Graphs unnecessary fragment complex descriptions into 
> (very) small piece due to their provenance descriptions*. So when you 
> would like to query this complex description at once you may have to 
> include many Named Graphs. This makes the SPARQL query rather complex.
> A current workaround is to duplicate this fragmented knowledge into a 
> default graph to be able to easily query such complex descriptions 
> (without their provenance information). 

But this is what (most?) triple stores do with the default graph in the 
absence of FROM/NAMED clauses in queries anyway. (Certainly this is the 
Sesame approach, followed by OWLIM.)

> This increases the maintenance costs as well and the (originally) 
> related knowledge is now decoupled.

I didn't understand this - can you clarify? (I'm tempted to think you're 
talking about a real duplication, rather than the default construction 
of the default graph)

> On the other side, many triple store vendors are already utilising 
> statement identifiers internally. So why not utilising them externally 
> as well by introducing URIs instead of internal identifiers.

Well, the cost is in indexing a large number of small graphs for 
efficient querying (especially in the presence of queries with unbound 
graph IDs). This does seem to become a common requirement these days though.

The biggest issue is 'giving up' your one chance at a utilisation for 
named graphs, since these are not hierarchical or applied as a set to 
triples. This, though, is an old argument...

Received on Wednesday, 22 February 2012 17:30:31 UTC

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