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Re: rdf-star#121 moots "Re: drop referentially opaque semantics in embedded triples"

From: Pierre-Antoine Champin <pierre-antoine.champin@ercim.eu>
Date: Mon, 17 May 2021 19:54:11 +0200
To: Paul Alagna <pjalagna@gmail.com>
Cc: public-rdf-star@w3.org
Message-ID: <e1269238-039a-5792-a764-a19702897f5f@ercim.eu>
Paul,

On 17/05/2021 19:22, Paul Alagna wrote:
> One day I will finish my thoughts before I hit the send button
> All;
> Please clarify this for me.
> If our ontology is given
> ====
>     :superman owl:sameAs :clark.
>     :superman :can :fly.
>
> ====
>
> Why would SPARQL ever use the “=“ symbol to operate on  ( :superman 
> owl:sameAs :clark. ) to find that equivalence?
>     SELECT (:superman = :clark as ?x) {}

That's a fair question. Another way to ask that question would be

   ASK { :superman owl:sameAs :clark }

and then the answer would be 'True'.

My point was precisely to demonstrate that the '=' operator in SPARQL is 
not entirely aligned with owl:sameAs, and so that "equality according to 
SPARQL" is not  equivalent to "co-denotation according to the formal 
semantics".

>
> ====
> If we rewrote the graph
> To say
> :superman = :clark.
> :superman :can :fly.

The '=' operator of is not an RDF predicate. ':superman = :clark' is an 
expression that can be used in some places of a SPARQL query, but not a 
statement that can be stored in the dataset.

>
> Wouldn’t SPARQL behave as expected?
It would raise an error, which is to be expected, for the reasons stated 
above ;-P
> OR
> re-query SPARQL to ask
> SELECT (:superman owl:sameAs :clark as ?x) {}

This would also raise an error, because what appears before 'AS' must be 
an expression. Here, you put a statement, which is syntactically incorrect.

What you probably want to write here is the ASK query I wrote above.

>
> I guess my question is: what are you expecting SPARQL to do? and why 
> does that hinder what you enter into your graph?

The relationship between SPARQL and RDF's semantics is non trivial.

There are several "flavours" of the semantics (simple, RDF, RDF-S, 
OWL-EL, OWL-QL, OWL-RL, OWL-DL...), and each of them has a well defined 
relationship to SPARQL (see https://www.w3.org/TR/sparql11-entailment/).

It does not hinder what you enter in your graph, but it determines how 
inferred information you can expect in your SPARQL results.

   hope this helps

>
>
> ============================
>
> All;
> Please ??
> If our ontology is given
> ====
>
>     :superman owl:sameAs :clark.
>     :superman :can :fly.
>
> ====
>
> Why would SPARQL ever use the “=“ symbol to operate on  ( :superman 
> owl:sameAs :clark. ) to make that equivalence?
>
>     SELECT (:superman = :clark as ?x) {}
>
> ====
> If we rewrote the graph
> To say
> :superman = :clark.
>  :superman :can :fly.
>
> Wouldn’t SPARQL behave as expected?
>
> I guess my question is: what are you expecting
>
>
>> On May 15, 2021, at 5:41 PM, James Anderson 
>> <anderson.james.1955@gmail.com 
>> <mailto:anderson.james.1955@gmail.com>> wrote:
>>
>> good evening;
>>
>> once a decision is reached on how to compare rdf-star triples[1], 
>> will that determination not render the issues concerning referential 
>> behaviour moot?
>>
>>
>> without regard to whether sameness is to be governed by term identity 
>> or value equality, in either case, the proposed resolution reads as 
>> if the relation is to be determined free of context.
>> on those terms, according to the sense of "referential transparency" 
>> which i would think carries over from programming language 
>> semantics[2] - and as such, would be one which i would chose to 
>> govern my implementation efforts, the embedded triples are 
>> referentially transparent.
>>
>> the longer i have witnessed these discussions, the more they have 
>> confounded me.
>> during the 14.5.2021 call, in particular, where notions which had 
>> been discussed in other contexts in relation to n3 were introduced 
>> into the discussion, ostensibly in support of the "referential 
>> opacity" imperative, i was most confused, as my (mis?)understanding 
>> of the n3 situation - from having read the arndt-van-woensel and and 
>> berners-lee expositions [3,4], had been the opposite.
>>
>> so i re-read arndt [3], again.
>> as it were, i am left still with the conclusion that, despite the 
>> rhetoric, the substance of the argument is that the expressions - in 
>> their case the n3 formulae and in the rdf-star case the embedded 
>> triples, are necessarily referentially transparent.
>> were that not the case, much of their argument would not be necessary 
>> and other aspects could not succeed.
>> what [3] describes is various ways to construct interpretation 
>> contexts and their consequential semantics.
>> in all cases, the formulae themselves are transparent: they, 
>> themselves, always refer respectively to the same thing.
>>
>> from which perspective, the discussions related to rdf star can never 
>> resolve until they shift from the semantics of the triple - which the 
>> resolution to #121 will specify, to that of interpretation context(s).
>> the current approach - to argue about the one as a surrogate for the 
>> other, has yet to succeed.
>>
>> best regards, from berlin,
>> - - -
>> [1] : https://github.com/w3c/rdf-star/issues/121 
>> <https://github.com/w3c/rdf-star/issues/121>
>> [2] : 
>> https://scholar.google.com/scholar?q=The+Scott-Strachey+Approach+to+Programming+Language+Theory 
>> <https://scholar.google.com/scholar?q=The+Scott-Strachey+Approach+to+Programming+Language+Theory>
>> [3] : http://ceur-ws.org/Vol-2438/paper6.pdf 
>> <http://ceur-ws.org/Vol-2438/paper6.pdf>
>> [4] : https://arxiv.org/pdf/0711.1533.pdf 
>> <https://arxiv.org/pdf/0711.1533.pdf>
>>
>>
>

Received on Monday, 17 May 2021 17:54:33 UTC

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