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

Re: Metadata about single triples

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Wed, 22 Feb 2012 13:18:15 -0500
Message-ID: <4F453167.2030203@openlinksw.com>
To: public-lod@w3.org
On 2/22/12 12:30 PM, Barry Norton wrote:
> 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.)

Not so re. Virtuoso. The Graph IRIs don't matter. Only used them if you 
explicitly seek to constrain the dataset from which you seek a SPARQL 
based solution.

>> 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)

Same data across different Graph IRIs != duplication.
>> 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...

See my comment above re. use of Graph IRIs re. SPARQL. They can serve as 
Named Partitions for your data. You may have a variety of reasons for 
having the same triples across many Named Graphs. Nothing wrong with 
that :-)

> Barry



Kingsley Idehen	
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Received on Wednesday, 22 February 2012 18:18:42 UTC

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