Re: possible stances with respect to multiple reification

Obviously, we should go with option (1).

On 22 Apr 2024, at 16:45, Franconi Enrico <franconi@inf.unibz.it> wrote:

On 22 Apr 2024, at 16:17, Lassila, Ora <ora@amazon.com> wrote:

I really would like to see how far we could take the idea of "well-formedness". I understand it may not be easy to formalize, but I am sure we could do better than what people say about pornography ("I cannot define it but I know it when I see it"). Implementations could accept non-well-formed graphs, or reject them. In case they do accept them, outcomes could be unpredictable (ranging from practically nothing to annoying or worse). People building systems that rely on predictable behavior on non-well-formed graphs would be "on their own”.

Yes, but I understand that the issue here is what you do define to be a well-formed graph.
I see at least two possibilities here:


  1.  Well-formed graphs include all the cases for which we have relevant use cases; this coincides exactly with rdf:reifies being many-to-many.
It is easily formalisable as an abstract grammar - see <https://github.com/w3c/rdf-star-wg/wiki/RDF%E2%80%90star-semantics%3A-option-3#best-practices-for-reification-and-reification-well-formedness>.
A “best practices” Section/document will explain how to encode the relevant use cases as well-formed graphs.
  2.  Well-formed graphs include only rdf-reifies being many-to-one.
It very hard to formalise it in an acceptable way as an abstract grammar (see counterexamples by Pierre-Antoine).
Non well-formed graphs are described as having non-predictable outcome wrt rdf:reifies, even if in many cases they would have a perfectly valid meaning wrt rdf:reifies (namely, the many-to-many cases above).

Obviously, we should go with option (2).
cheers
—e.