Re: Decision from the Semantics TF: liberal baseline

Dear Pierre-Antoine,

> Am 07.01.2025 um 17:01 schrieb Pierre-Antoine Champin <pierre-antoine@w3.org>:
> 
> My 2 ¢ about https://github.com/w3c/rdf-star-wg/wiki/RDF-star-%22liberal-baseline%22#rdf-semantics
> 
> - for the sake of homogeneity, I would keep only reif1 and reif2 in RDF Semantics,
>   and push reif3 in RDFS Sedmantics (which would simply mean to add the axiomatic triple rdf:reifies rdfs:range rdf:Proposition . This is for the sake of regularity. I don't think that RDF semantics has any "range-like" entailment for the moment.

I personally agree with you, but where to put that rule als depends on what we want in general. There is the possibility to make rdf:reifies  some kind of „special“ predicate for which we derive that the subject is always a rdf:Proposition even when occurring nested. I  really do not want to have something like that for all domain declarations. So, if we want to make that the subject of rdf:reifies is always a rdf:Proposition regardless of it occurring nested or not, then it should be done like that. Whether we want that is of course a different question.


> 
> - regarding the distinction between "if S contains" and "if the triple structure appears in S", I think I would prefer to keep "if S contains" for all entailment patterns. What happens in a triple term stays in a triple term. People may want to talk about non-sensical triples, and any inference transpiring from triple terms may make this inconsistent.

I understand your concern and lean towards your opinion. However, I try argue against that following the arguments I understood them from our semantics meeting:

Being a proposition or not  could be seen as some kind of syntactical statement. 


I try to make a comparison with predicates.

If we state a simple triple

:s :p :o.

We can derive with rdf entailment that

:p a rdf:Property.

Now, the question is, should we also derive from

:a :b <<( :s :p :o)>>.

that

:p a rdf:Property. ?

Note that the semantics as it is does that, because RE has IR x IP x IR as domain (and not IR x IR x IR). We would somehow make the assumption that even though the quoted triple could be wrong, it is syntactically correct (whatever that means).

If we follow the same line of argumentation, we could say that from

:a :b <<( :s :p <<( :x :y :z )>>)>>.

We can still derive that

 <<( :x :y :z )>> a rdf:Proposition.

We again assume all statements to be syntactically correct (note that „syntactically correct“ is a horrible naming, maybe „structural semantics“?). 


From another angle: if we go RDFS, do we want to have entailment rules which lead from

:s :p <<( :x :y :z )>>.

to

:x a rdfs:Resource. ?

If so, would the step from

:a :b <<( :s :p <<( :x :y :z )>>)>>.

to

 <<( :x :y :z )>> a rdf:Proposition.

be similar? Maybe we should add some entailment of that kind to RDFS instead of RDF?


I did not make up my mind yet, how I see these propositions. What do the others think?

Kind regards,
Dörthe






>   pa
> 
> 
> On 07/01/2025 16:16, Franconi Enrico wrote:
>> On 7 Jan 2025, at 15:44, Doerthe Arndt <doerthe.arndt@tu-dresden.de> <mailto:doerthe.arndt@tu-dresden.de> wrote:
>> 
>>> I noticed that you used the wording "if the triple structure appears in S“ for the conditions.
>>> From your e-mail I assume that „triple structure appears in“ is not the same as the original „S contains“ we have for the other patterns and that you changed the wording to deal with nesting.  
>> 
>> Correct.
>> 
>>> I think we need to be very clear what this means and that we include nesting here.
>> 
>> Sure.
>> 
>>> Here we also come to the question you raised in the mail. So, from your point of view you would always want to have this „triple structure appears in“ notion? Or would you want to have some distinction between „triple structure appears in“ vs „triple is element of S“? Where else would we need the first notion?  
>> 
>> I  want to hear comments from other people about how to define  these metamodelling properties (about which, as I have been abundantly made clear, I couldn’t care less 😀).
>> For elegance and symmetry, I am tempted to have the „triple structure appears in“ notion.
>> However, please note the following example:
>> :john :believes _:r1 .
>> _:r1 rdf:reifies <<(:paul rdf:type :canadian)>> .
>>     currently does NOT rdfs entail
>> :canadian rdf:type rdfs:class .
>> :paul rdf:type rdfs:resource .
>> 
>> That is, metamodelling entailments within nested triple terms do not currently hold.
>> So, either we change all the RDF/RDFS entailments to hold also in nested triple terms (rather impactful), or we allow for entailments only at top level.
>> The above example suggests that we should allow for entailments only at top level (and so I have to revert to the previous version of the semantics).
>> What do you (and anybody else) think?
>> 
>>> According to the semantics as you have it at the moment, we would need „triple structure appears in“ for both current RDF entailment patterns, right?
>> 
>> Yes.
>> 
>> —e.
>> 
>> 
>>>> Am 02.01.2025 um 17:29 schrieb Franconi Enrico <franconi@inf.unibz.it> <mailto:franconi@inf.unibz.it>:
>>>> 
>>>> At the last Semantics TF we discussed about the RDF semantics of the liberal baseline.
>>>> In the current version of the document:
>>>> https://github.com/w3c/rdf-star-wg/wiki/RDF-star-%22liberal-baseline%22#rdf-semantics
>>>> the two discussed restrictions of RDF semantics are formalised:
>>>> triple terms, appearing in triples or in triple terms, are of type rdf:proposition;
>>>> objects of the property rdf:reifies, appearing in triples or in triple terms, are of type rdf:proposition.
>>>> We may decide to have both restrictions, any of them, or none.
>>>> Let’s open the general discussion :-)
>>>> —e.
>>>> 
>>>>> On 13 Dec 2024, at 18:20, Franconi Enrico <franconi@inf.unibz.it> <mailto:franconi@inf.unibz.it> wrote:
>>>>> 
>>>>> Today the Semantics TF met, and we agree to submit to the working group a proposal for a liberal baseline.
>>>>> It is summarised in <https://github.com/w3c/rdf-star-wg/wiki/RDF-star-%22liberal-baseline%22> <https://github.com/w3c/rdf-star-wg/wiki/RDF-star-%22liberal-baseline%22>, to be discussed (and voted?) at the first focussed meeting in 2025.
>>>>> Basically, there will be a no syntactic restriction in using both rdf:reifies and triple terms.
>>>>> Reification is sanctioned only if it makes use of the property rdf:reifies or any of its subproperties; the subject of rdf:reifies is called a reifier.
>>>>> Triple terms would be always of type rdf:Proposition, and the range of rdf:reifies would be rdf:Proposition.
>> 
>>