Proposal draft: Support RDF 1.2

[Ostrzyciel]

RDF 1.2 is still in flux, but early implementations (e.g., in Apache Jena) are already available. This already gives ideas on the possible migration paths from RDF-star: Jelly-RDF/jelly-jvm#351

Let's wait patiently for at least a consensus note from the WG. I'm leaving this task here to collect any materials / ideas early.

This should batch together a few bigger changes to the protocol:

• Implement Proposal draft: packed lookup entries #41
• Implement Proposal draft: trivially mergeable Jelly files #102
• Deprecate producing RdfTriple and RdfQuad. Instead introduce a unified RdfStatement, like in Jelly-Patch (Proposal: Jelly extension for RDF Patch #11).
  • Now the physical stream type decides whether we are looking at triples or quads.
  • Reorder the fields such that well-formed RDF fields are in the 1-byte tag range, and generalized RDF always falls into the 2-byte range.
  • Reuse this new message in Jelly-Patch.
• Deprecate producing the GRAPHS stream type. It does not offer any advantage vs QUADS, when repeated term compression is used.
• Introduce support for RDF 1.2 features: triple terms, possibly Turtle-like RDF 1.2 shorthands, text direction.

[Ostrzyciel]

See also: eclipse-rdf4j/rdf4j#5327

[Ostrzyciel]

I talked to the RDF & SPARQL WG on TPAC yesterday.

The short version is that the spec from the RDF side is not expected to change anymore, so we should be very much fine with implementing it right now in Jelly.

The WG does not have and does not plan to have a defined migration path from RDF-star. We just break compat and that's it. RDF-star was never a standard.