Re: the rationale and history of RDF-star semantics

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.
>
> 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

>>