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Re: Comments on PAQ

From: Timothy Lebo <lebot@rpi.edu>
Date: Fri, 2 Dec 2011 16:42:54 -0500
Cc: "Cresswell, Stephen" <stephen.cresswell@tso.co.uk>, Paul Groth <p.t.groth@vu.nl>, Provenance Working Group WG <public-prov-wg@w3.org>
Message-Id: <81897298-4DC6-4880-ABD2-F01AC025D17D@rpi.edu>
To: Graham Klyne <GK@ninebynine.org>
Graham,

I've mention these links a few times over the past months, but I think they might touch upon some of what you're wrestling with.
I know I'm certainly wrestling with it and hope that the PAQ can help me.

I realize that these pages mean more to me than what they say, but I hope they will be helpful in sparking ideas or discussion.



Listed so that most recent is first:


http://www.w3.org/2011/prov/wiki/Reflections_from_RDF-WG_F2F2
is a slightly "from scratch" perspective on the problem of "getting at" a named graph hidden behind a SPARQL service.


http://www.w3.org/2011/prov/wiki/Using_named_graphs_to_model_Accounts
wrestles with the different meanings of "named graph" - one of which is the RDF 1.1 WG's GraphContainer (that currently doesn't have a standard way to identify)


https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd:NamedGraph
offers a technique to awww:identify the named graph within the context of a SPARQL service


Regards,
Tim



On Nov 19, 2011, at 3:55 AM, Graham Klyne wrote:

> Stephen,
> 
> Thanks for your comments.
> 
> On 18/11/2011 12:59, Cresswell, Stephen wrote:
>> 
>> 
>> Graham, Paul,
>> 
>> 
>> 
>> I have a few comments on PAQ document (not obstructing its release).  I
>> read it from the perspective of needing to decide on some solution to
>> deploy.  I think the document works and I learned quite a lot reading
>> from it.  The biggest question I had was why some possibilities seem to
>> be missing, which I think Luc already flagged. I just wanted to
>> emphasise this because (unless I misunderstand it) the missing
>> possibilities are (from my perspective) some of the most important ones.
>> 
>> 
>> 
>> I got these:
>> 
>> If a resource is published by HTTP, or it is HTML or XHTML, then we can
>> link to provenance by provenance-uri or provenance-service-uri.
>> 
>> If a resource is some form of RDF, then we can give provenance-uri (but
>> apparently not a provenance-service-uri?).
> 
> You're the second person to raise this, and on reflection I'm finding it harder to justify the asymmetry.  (Originally I had this idea that the RDF case was somehow different, or aiming at use-cases where the provenance service made less sense, but on reflection I find it hard to sustain that argument.)
> 
> I've raised this as ISSUE 154 (http://www.w3.org/2011/prov/track/issues/154).
> 
>> Despite the coverage of querying provenance in SPARQL, the document
>> doesn't tell us how to publish a resource and indicate that its
>> provenance can be retrieved from a particular SPARQL endpoint (using a
>> given entity-uri and/or a given named graph).  Neither does there seem
>> to be a way for a provenance service to give back a link to a SPARQL
>> endpoint.  SPARQL endpoints can be self-describing through SPARQL
>> service descriptions, but surely we still need to be able to indicate
>> that a URI provided for provenance is a SPARQL endpoint.  That seems to
>> be a conspicuous gap.
> 
> I see two possible points here:
> (a) how to publish a resource and associated metadata accessible via SPARQL
> (b) how to specifically indicate a SPARQL endpoint for retrieving provenance
> 
> (a) Hmmm... my original assumption had been that developers using SPARQL would know how to deploy a SPARQL endpoint.  I think my preference would be to reference some existing documentation, rather than try to write a description of how to do this.   (I think you are not actually suggesting this, but I thought I'd cover it just in case.)
> 
> (b) I agree there is a gap here:  the link relations introduced are intended to be used with direct URI retrieval scenarios.  (In theory, the provenance service description could provide a template that encodes a SPARQL query URI, but I'm not confident that's a practical option.)
> 
> I am conflicted about this as I think this takes is into the general territory of query endpoint discovery - I imagine a SPARQL service would typically not be used *only* for provenance.  If there are existing techniques we can reference, I'd be completely happy to include references to them.  I'm less comfortable about defining provenance-specific mechanisms that are likely to overlap non-provenance requirements.  I think the natural mechanism would be to introduce a new link relation to designate a corresponding SPARQL endpoint.
> 
> I'll ask around.
> 
>> Section 5.3 - Did you consider using "DESCRIBE
>> <http://example.org/resource>  {}" instead of the CONSTRUCT query?
> 
> No, I didn't consider that.  Using DESCRIBE is not excluded (this section provides examples of possible use rather than prescriptions).
> 
> Personally, I'm not a fan of DESCRIBE as a standard construct because it doesn't have an interoperable specification, and there's no framework for naming interoperable versions - but I know I'm in a minority here - my comments to this effect to the SPARQL working group were not accepted.
> 
> But for specific applications, I recognize that DESCRIBE can be a useful mechanism, and if you think it makes the document more useful I'm not against adding it as another example.
> 
>> C.1 Gap Analysis - drops into 1st person (not in an annotation).
> 
> Yes - it's out of style.
> 
> I'd like to remove this section - I think it has served its purpose, and is now somewhat outdated.  I've raised this with my co-editor.
> 
> #g
> --
> 
> 
Received on Friday, 2 December 2011 21:43:40 GMT

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