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Re: RDF-ISSUE-17 (graph merge): How are RDF datasets to be merged? [RDF Graphs]

From: Axel Polleres <axel.polleres@deri.org>
Date: Tue, 29 Mar 2011 14:04:46 +0100
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <4A7F0E88-75B2-44A4-913C-5D79AEAF37E8@deri.org>
To: Steve Harris <steve.harris@garlik.com>
Hi all, 

just to understand... Having an additional Dataset-MERGE definition in the SPARQL-Update doc, doesn't seem to be a problem, I agree.
However, it wouldn't necessarily be used in SPARQL itself (probably not a big problem)

</rdfwg>
... wait a second... thinking out loud here, {RDF-WG ignore this, SPARQL WG members... I will post this on SPARQL separately)

thinking about e.g. the LOAD operation in SPARQL update [1], we might actually to prefer it in terms of Dataset-MERGE instead of Dataset-UNION.
i.e. we don't want a graph loaded from externally intermingle with the bnodes already in a graph store.

Note that this may also affect the ADD operation...  where you may actually which to keep bnode labels separate? But that's not necessarily an issue, because I guess we may assume rthat bnode labels are disjoint within disjoint graphs within a graph store anyways...

1. http://www.w3.org/2009/sparql/docs/update-1.1/Overview.xml#def_loadoperation
<rdfwg>

That actually brings me back to RFG: Can/Shall we assume within a dataset in RDF that graphs within the same dataset don't share bnode identifiers? I think this could be a useful assumption and make many things easier.

Axel 


On 29 Mar 2011, at 09:57, Steve Harris wrote:

> Yeah, I agree - it's the most logical place to look for it.
> 
> - Steve
> 
> On 2011-03-28, at 20:38, Andy Seaborne wrote:
> 
>> Wouldn't it be better to put the RDF datasets merge definition along side the RDF dataset definition to put everything in one place? Splitting across docs isn't great.
>> 
>> http://www.w3.org/2009/sparql/docs/update-1.1/Overview.xml#def_datasetUnion
>> 
>> and s/union/merge/g ; s/graph store/RDf dataset/g ;
>> 
>> 	Andy
>> 
>> On 28/03/11 16:07, RDF Working Group Issue Tracker wrote:
>>> 
>>> RDF-ISSUE-17 (graph merge): How are RDF datasets to be merged? [RDF Graphs]
>>> 
>>> http://www.w3.org/2011/rdf-wg/track/issues/17
>>> 
>>> Raised by: David Wood
>>> On product: RDF Graphs
>>> 
>>> The "RDF Semantics" spec defines how to merge two or more RDF graphs,
>>> the pain is caused by blank nodes, otherwise it's a trivial operation.
>>> 
>>> The "SPARQL Query Language for RDF" spec defines the notion of RDF
>>> dataset as a set of "one graph, the default graph, which does not have
>>> a name, and zero or more named graphs, where each named graph is
>>> identified by an IRI".
>>> 
>>> How do we define how to merge RDF datasets?
>>> 
>>> One obvious answer is we merge all the default graphs and all the
>>> named graphs with the same IRI using the procedure defined by the "RDF
>>> Semantics" to merge RDF graphs.
>>> 
>>> NB: This issue will also relate to the "Cleanup Tasks" product if the RDF Semantics document will need to change in relation to named graphs.
>>> 
>>> At Talis, within the Talis Platform, we want to enable people to
>>> easily merge RDF graphs into an RDF dataset and perhaps RDF datasets
>>> into another RDF dataset. We also want to have these merge happen in
>>> real-time (i.e. as you add/remove triples from the graphs you update
>>> all the derived graphs/datasets).
>>> 
>>> Thanks to Paolo Castagna of Talis for providing input to this issue.
>>> 
>>> 
>>> 
>>> 
>> 
> 
> -- 
> Steve Harris, CTO, Garlik Limited
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Received on Tuesday, 29 March 2011 13:05:20 UTC

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