On https://meta.wikimedia.org/wiki/Wikidata/Notes/URI_scheme#Proposal_for_Wikid... I am missing the arguments why Wikidata needs the multitude of URI forms. The list needs commenting and arguments why
"URIs should be canonical within Wikimedia projects"
is given up.
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(Of lesser importance, I wonder why the internal opaque ID has to be prefixed by a letter (Q) - why not a simple number?)
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At them moment I believe a choice should be made between: http://%7Bsite%7D.wikidata.org/wiki/%7Btitle%7D and http://wikidata.org/title/%7Bsite%7D:%7Btitle%7D but perhaps the argument why both are needed could be added.
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On the issue of interlanguage/interwiki linking, I believe the semantics should not be opposite in Wikidata and Wikipedias, see my comment https://meta.wikimedia.org/wiki/Talk:Wikidata/Notes/Wiki_links
Gregor