On 27/02/2020 13:46, Ethan Gruber wrote:
I really disagree with alternative URL patterns and using them in RDF. That URL
pattern is *not* the concept,
The URL has well-defined semantics (e.g.) "this is Richard Light's CRM
rendition of the Geonames place Burgess Hill". It's a derived concept.
and whomever generates these URLs is responsible for maintaining them
permanently.
Absolutely. If someone sets up a (sub-)domain to provide this sort of service,
they should do so with the same degree of commitment as someone setting up a
Linked Data resource from scratch. But then, if we can never get to the point
of trusting, and using, 'someone else's URLs', we will forever remain cowering
in our silos, as I mentioned below. And our data would not, in any useful
sense, be Linked Data.
A web service like this works in theory, but I would say that the majority of
the LOD-oriented vocabulary systems used in cultural heritage do not come with
SPARQL endpoints. Each of them offers some flavor of machine-readable data, so
you'd have to build your web service around REST calls for RDF/XML or JSON and
building a mapping from those serializations into Linked Art JSON-LD.
Yes, you probably would [have to do this]. So you would need to decide whether
it was worth the investment in the mapping work and software development, given
the scale and utility of the resource this would give you (and everyone else)
access to. I don't see that as an argument for not adopting the approach at
all.
Also, please note that I am discussing this in the context of the CRM SIG, not
Linked Art. So the service would simply aim to generate a generic CRM-valid
sub-graph. Also, I would expect it to offer a reasonable range of
serializations, not just JSON-LD.
The best solution is to relax CIDOC CRM to allow people to use vocabularies
that aren't built on CIDOC CRM. Domains and ranges should be considered
guidelines, not absolutes. There's nothing technically prohibitive about
inserting CRM linking to Getty URIs describing artistic objects into a SPARQL
endpoint, and also loading those Getty vocabularies into the same endpoint, and
then building SPARQL queries that exploit the capabilities of both data models.
Using property paths in SPARQL are more scalable in production than activating
inferencing engines.
That's sort of where I started from ("be relaxed about the semantic
discontinuity" below). However, I suspect there are members of this group who
would be far from relaxed about this.
As it happens, another respondent has just pointed out what looks like a
solution to the original problem which exercised the Linked Art group (using
ULAN and TGN in a CRM-compatible setting), and I have forwarded their comments
to that group.
Richard
Ethan
On Thu, Feb 27, 2020 at 7:01 AM Richard Light
<rich...@light.demon.co.uk<mailto:rich...@light.demon.co.uk>> wrote:
Hi,
The Linked Art group has been discussing the issue of URIs which point to
resources in other frameworks
(https://github.com/linked-art/linked.art/issues/307). The discussion has noted
the advice in our RDF implementation document
(http://www.cidoc-crm.org/sites/default/files/Implementing%20the%20CIDOC%20Conceptual%20Reference%20Model%20in%20RDF_0.pdf),
in particular the advice that skos:Concept should not be used for people or
places. This raises an issue in relation to ULAN and TGN, two Getty
vocabularies which Linked Art would expect to be able to use. Various
work-rounds have been proposed, of varying complexity.
After giving this issue some thought, I contributed the following to the
discussion:
Interesting problem. This issue will crop up wherever you want to exploit the
potential of Linked Data by linking out across a 'boundary' to a LD resource
which plays by different rules to your own. So it's not just a Linked Art
problem. The alternatives would appear to be:
* be relaxed about the semantic discontinuity
* insist the rest of the LD world changes to fit your world view (which
appears to be the CRM SIG position)
* cower inside your silo and ignore everything outside it
I would argue for adopting the first option. The external resource will still
dereference for you; it will still deliver a machine-readable payload. As
mentioned above, you won't find any Linked Art or CRM concepts in there, but
does that matter?
There might be benefit in inventing a relationship for Linked Art which says,
in effect, "this is an equivalent but 'external' concept".
To go beyond this, assuming that resources such as Geonames will continue to
happily ignore our existence, I would suggest a dynamic mapping service, which
takes e.g. a Geonames URL, retrieves its contents, and re-expresses those
assertions in a CRM-compatible format. Make the call to that service a URL in
our Linked Data with the Geonames URL as a parameter, and we will have extended
our Linked Data graph to include a virtual CRM-compatible Geonames. Rinse and
repeat with other external resources which are big enough to be of interest to
us, and too big to re-design along CRM lines.
On reflection, I increasingly like the idea of a dynamic mapping service. Maybe
we should add something along those lines to the RDF implementation document?
The way it would work could be as follows:
* we analyse the RDF which is generated by the external resource and
re-express those parts of it which are CRM-compatible in CRM RDF (i.e. do a
mapping). Some concepts may not map, and would be excluded from the process
* we develop a web service which implements this mapping, taking one URL
from the external resource as its input and returning CRM RDF
* we support a variant URL pattern which maps to this web service, e.g.
https://geonames.cidoc-crm.org/2654308/ for
https://www.geonames.org/2654308/burgess-hill.html
* CIDOC CRM users quote these variant URLs in their RDF data
This approach makes no demands on the external system; it simply exploits the
fact that it is providing machine-processible data. Once installed, it will
deliver whatever resources are in the external system, i.e. you don't need to
keep updating your 'copy'. In effect, it extends the scope of the
CRM-compatible graph to include this external resource (and all the resources
that it mentions).
Where the external resource has a SPARQL end-point, it may be possible to
implement the mapping (at least in simple cases) by a suitable CONSTRUCT
statement.
Thoughts?
Richard
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