Hi,
I have encountered a problem with federating Wikidata entities with LOD
based on the abundant external resource "literal identifiers" that are
represented in Wikidata. An external resource identifier should include
the entire IRI to the resource, not just the "id", otherwise the external
resource cannot be federated in a SPARQL query without concatenating the
IRI to the literal identifier and binding to a new variable.
I think that Wikidata properties that expect explicit Identifiers in the
range should thus be defined as "object properties" rather than "datatype
properties". The javascript id linking gadget in the UI also typically
borks the link when a IRI is inputted as an identifier making it less
likely for people to do it properly. I assume that this is a "policy" that
was established for bot id imports, that unfortunately has produced a lot
of "not so useful" data.
The triple pattern fragment implementation that I am working with does not
allow bind grouping in the sparql query, so this unfortunately makes
federation of Wikidata entities by Identifiers nearly impossible. Hence,
the only federation that I have been able to do effectively is "to"
Wikidata not "from" it....
If anyone is interested, I have setup Wikidata as a TPF datasource here:
http://orbeon-bb.wmflabs.org/wdqs-sparql The API works by passing an
encoded subject, predicate or object parameter like:
http://orbeon-bb.wmflabs.org/wdqs-sparql?object=%22Berlin%22%40de
Christopher