Re: the rationale and history of RDF-star semantics

On tor, 2023-01-19 at 21:57 +0100, Pierre-Antoine Champin wrote:
> On 19/01/2023 02:32, Peter F. Patel-Schneider wrote:
> > How far does this history go back?  Wasn't the original semantics for RDF* a semantics that treats embedded triples
> > as syntactic sugar for RDF reification?
> > 
>  My point was indeed to give a rationale of what we have done in the CG -- I was not involved in earlier proposals of
> RDF*, I can not speak for that.

I can. The semantics of RDF* was not the most thought-through aspect of the original proposal. I think that this has
become clear during the work of the RDF-star CG. The main focus of the original work was more on the syntactical
concepts of the data model (i.e., nesting of triples), the corresponding user-facing syntax (Turtle*), and---in
particular---the corresponding extension of the SPARQL language.

Olaf


> > peter
> > 
> > 
> > On 1/17/23 08:35, Pierre-Antoine Champin wrote:
> > > Dear Enrico, all,
> > > following the discussion we had during the last call [1], I would like to give a more detail overview of our
> > > rationale           when designing the RDF-star semantics in the CG report [2], and defuse a few
> > > misunderstandings.
> > > 
> > > 1. It was not the intention to make RDF-star a modal logic
> > > 
> > > I know that examples such that ":alice :belives << :s :p :o >>." strongly point in the direction of modal logic,
> > > and that such examples have been largely used to "sell" RDF-star. I agree that such examples are misleading, and
> > > we actually tried to avoid such examples in the CG report.
> > > 
> > > The intention was to make RDF-star quoted triples opaque, and providing as little inferences as possible --
> > > leaving it open for semantic extensions to provide more inferences.
> > > 
> > > 
> > > 2. Ground quoted triples are similar to literals
> > > 
> > > Our initial attempt was to define from scratch a model theoretic semantics of RDF-star, where ground quoted
> > > triples (i.e. quoted triples containing no blank node) were constrained to denoted themselves. In other words, we
> > > consider that RDF(-star) triples (as defined by the specification) are conceptual objects that exist in the world
> > > (in the same way that graphs, classes and properties exist), and that ground quoted triples did denote exactly
> > > them.
> > > 
> > > In that sense, ground quoted triples are very much like literals (except that they are allowed in the subject
> > > position).
> > > 
> > > 
> > > 3. Blank node rain on our parade (as they usually do)
> > > 
> > > Of course, things get tricky when we take blank nodes into account.
> > > 
> > > Just like the RDF1.1 Semantics, our proposal was built in two steps :
> > > - define the semantics of ground RFD-star graphs (following the rationale described above)
> > > - deal with blank node
> > > 
> > > The second step was quite complicated, and it raised some questions about whether this brand new semantics was
> > > sound. An alternative way was therefore proposed, to rely on the battle-tested RDF semantics. And that's where we
> > > are now.
> > > 
> > > Honestly, I would rather give another try at adapting the current RDF semantics to take into account quoted
> > > graphs, than keeping the layered approach that we currently have. 
> > > 
> > >   pa
> > > 
> > > 
> > > [1] https://www.w3.org/2023/01/12-rdf-star-minutes.html#t03

> > > [2] https://www.w3.org/2021/12/rdf-star.html#rdf-star-semantics

> > >

Received on Thursday, 19 January 2023 22:12:21 UTC