purl, vocabularies and ivoa.net

[Franck Le Petit]

Dear colleagues,

I also agree with the proposition of Markus to use fragment identifiers rather than paths and to keep the purl subdomain as explained by Nicolas. If I remember well that was also a recommendation of Norman Gray. 

Best regards
Franck



> Le 27 sept. 2017 à 15:59, nicolas moreau <nicolas.moreau at obspm.fr> a écrit :
> 
> Hi Markus,
> 
> We have no objection against the use of fragment identifiers. However we think is it necessary to keep the  purl subdomain.
> It will be easier then to configure a redirection to the page were the vocabularies are actually stored.
> 
> With the use of a fragment identifier, a typical identifier for a concept would be :
> 
> http://purl.ivoa.net/theory/vocabulary#ConceptName
> 
> 
> best regards
> 
> 
> 
> Le 26/09/2017 à 11:33, Markus Demleitner a écrit :
>> Hi Nicolas,
>> 
>> On Mon, Sep 25, 2017 at 11:33:31AM +0200, nicolas moreau wrote:
>>> We need to identify the concepts in our vocabulary.  To do so we
>>> would like to use URIs as ID. The nice thing about doing that is we
>>> can associate a representation (ex a SKOS XML subset, an HTML page,
>>> a .txt file, ...) with an ID (in this case an URI), which can
>>> change over time, while the ID remains unchanged.
>>> 
>>> Since these URIs will be identifiers we want them to be permanent
>>> and unique. Then we need a namespace in ivoa.net where to define
>>> permanent URIs, to be used as identifiers.
>>> 
>>> Adding a 'purl' segment to a path rooted inwww.ivoa.net  could be
>>> used, sure, the problem is that www carries representation semantic
>>> with it, that is HTML. We don't want the identifiers to be coupled
>>> with representation details, such as HTML, or SKOS, rdf or
>>> whatever. The 'purl' subdomain doesn???t carry much semantic with
>>> it and seems a perfect abstract place (namespace) where to define
>>> permanent URIs to be used as identifiers, IDs.
>>> 
>>> So we propose:
>>> purl.ivoa.net/theory/ConceptName<http://purl.ivoa.net/theory/ConceptName>
>> The purl part I have no strong feelings about.  I think www.ivoa.net
>> would work just as well, and it's what Datalink and Registry use, but
>> if you're it's not a big deal.
>> 
>> What I *would* like to see consistent within the VO is the use for
>> fragment identifiers rather than paths.  For instance, a preview in
>> datalink is
>> 
>> http://www.ivoa.net/rdf/datalink/core#preview
>> 
>> Why?
>> 
>> (1) this resolves to an actual document where people can find out
>> what preview is; in this particular document, there's no anchor yet,
>> but it's trivial to make sure a browser actually goes to a document
>> part containing preview's description.
>> 
>> (2) it meshes nicely with content negotiations.  A client that wants
>> to read turtle or RDF-X can just set an Accept header and will
>> retrieve the vocabulary in its preferred format; the semantics of the
>> fragment remains the same, even though the actual operations to
>> retrieve the fragment are, of course, format-specific.
>> 
>> (3) it also fits nicely with the vocabulary URI mechanisms in RDFa
>> and friends (but ok, these would also work with paths).
>> 
>> It's also reasonably easy to manage such vocabularies, keeping a
>> historical record of previous versions of the vocabularies (Datalink
>> and RegTAP already contain tooling to do that).
>> 
>>         -- Markus
> 
> 
> -- 
> -------------------------------------------------------------------------------------------------------------------
> Nicolas Moreau,  Observatoire de Paris-Meudon-Nancay
> LERMA 01 45 07 79 76 mail:nicolas.moreau at obspm.fr
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>