pchampin
commented
3 years ago See also the discussion on the mailing list: https://www.w3.org/mid/828395cf-d9e4-cad3-c051-c5ba88d27366@ercim.eu
Closing this PR, as it does not seem to convince anyone but me :-)
Here is an adaptation of the semantics, that I believe has some advantages over the current version:
it does not rely anymore on "hidden" predicates (#101)(I didn't formally prove the last two items, hence "I think"...)
The trick is that we do not map anymore RDF-star graphs to a single, semantically equivalent RDF graph. Instead, we map it to a pair of RDF graphs, which can be thought of as a "lower and upper bound" of the RDF-star graph, in terms of entailment. The semantics of the RDF-star graph is defined through the semantics of its "bounds", reusing RDF semantics as is (as we currently do).
In this new semantics, a strict RDF-star graph (i.e. one that contains embedded triples) has no exactly equivalent RDF graph, so it still can not be conveyed exactly using RDF syntaxes
(but we do not rely anymore on hidden predicates for that). However, either of the two "bounds" can be used to approximate the RDF-star graph in legacy RDF. The "lower bound" will produce correct but incomplete inferences. The "upper bound" will produce complete inferences, with a few spurious (but generally harmless) ones.edited since the "upper bound" entails the RDF-star graph, the initial version of this proposal still required RDF-star systems to "decode" embedded triples from their RDF descriptions, with all the trouble generated by pathological cases. So I re-introduced one hidden IRI to avoid that. Note however that the hidden IRI is now just a type; the description of the embedded triple is now mostly "visible" as RDF (as an extension of standard reification) -- although it does not entail, nor is entailed by, the embedded triple itself.
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