Hi James,
I'm not the best person to answer your questions (I've never actually used ShEx or contributed to it) but I hope to be able to answer your questions.
> I'm not clear whether there is an RDF representation of ShEx that could
be added to WDQS -- this is a point that would be useful to clarify;
and, if not, whether work is going on in this direction.
TL;DR: yes but it does not seem much used at the moment.
ShEx specifies [1] two syntaxes, ShExC that is the "plain text" syntax used on Wikidata and ShExJ that is based on JSON-LD. JSON-LD beeing an RDF seralization, there is indeed an RDF representation of ShEx. To get plain triples one could use the JSON-LD to RDF triples conversion algorithm that is implemented in most JSON-LD libraries. The old ShEx documentation pages refers to a ShExR serialization of ShEx to RDF but I believe it has been dropped in favor of ShExJ+JSON-LD to RDF conversion.
> It's not immediately clear to me whether SHACL adapts easily to
memberships defined by eg P31 "instance on" or P279 "subclass of"
statements, etc; also memberships possibly further defined or limited by
other statements.
Indeed Shacl 1.0 does not seem to be able to express it. There is an extension [1] that allows to specify targets using a sparql query, just like what is done with the ShEx playground using the focus nodes sparql query.
Thomas
[3] https://www.w3.org/TR/shacl-af/#SPARQLTarget
On 30/05/2019 17:45, Benjamin Good wrote:
> I'd like to restate the initial question.
>
> Why did wikidata choose shex instead of other approaches?
>
> From this very detailed comparison
> http://book.validatingrdf.com/bookHtml013.html (thank you Andra!) I could
> see arguments in both directions. I'm curious to know what swayed the
> wikidata software team as my group is currently grappling with the same
> decision.
>
One of the key differences would seem to be that SHACL has been
deliberately constructed to directly representable in RDF -- so a SHACL
expression could be put straight into WDQS and made queryable for what
it pertains to.
I'm not clear whether there is an RDF representation of ShEx that could
be added to WDQS -- this is a point that would be useful to clarify;
and, if not, whether work is going on in this direction.
IMO, it would be a very important asset to be able to query the Shape
specifications using SPARQL -- querying not for compliance, but for what
the specifications actually contain.
On the other hand, SHACL seems very strongly based on shapes for members
that are connected by an "is a" relationship.
It's not immediately clear to me whether SHACL adapts easily to
memberships defined by eg P31 "instance on" or P279 "subclass of"
statements, etc; also memberships possibly further defined or limited by
other statements.
It would seem a basic requirement, but I didn't see it on a first quick
skim-read.
-- James.
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