Re: A question about referential opacity (again)

It's important to be clear as to what is formal and what is informal in 
discussions of this sort.

Formally in the current semantics for RDF, all IRIs are mapped (via the map 
IS) to resources by interpretations in RDF.  One generally says that an IRI E 
denotes or refers to IS(E).

A formal semantics that provides for referential opacity of IRIs generally 
provides a different mapping (let's call it IS') for IRIs that occur in opaque 
contexts, i.e., inside triple terms.   The details may differ, but the targets 
of this mapping are usually either left unspecified or are to some synthetic 
resources (such as copies of IRIs).

So if one was to construct an interpretation in this sort of formal semantics 
that actually included real cities in the world as resources and whose IS 
mapping mapped IRIs that are generally accepted as names of cities to the 
actual cities one would say that in transparent contexts, i.e., subjects, 
objects, and properties of asserted triples, dbr:Linköping refers to the city 
of Linköping but in opaque contexts, i.e., in triple terms, refers to 
something else.  (It may be possible that some interpretations dbr:Linköping 
in an opaque context does refer to the city, but the important point is that 
there are interpretations where dbr:Linköping in an opaque context does not 
refer to the city and that absent special constructs to force transparency on 
opaque contexts there is no way to force an RDF graph to be false in all these 
interpretations.)

peter

PS: The coordination group semantics uses a different mechanism entirely, 
instead syntactically transforming graphs that contain triple terms to regular 
RDF graphs.  Among other things, the opacity mechanism in this treatment 
transforms IRIs in triple terms to literal strings.  So part of this semantics 
is a relationship (similar to but not exactly denotes) from IRIs in opaque 
contexts to sequences of Unicode code points.

PPS:  There are other ways of obtaining opacity.  If the working group 
switches to graph terms the kind of semantics described above might not be 
adequate and some other treatment might have to be used.



On 10/21/23 07:00, Thomas Lörtsch wrote:
> Hi,
> 
> 
> Enrico was kind enough to guide me through the work of the Semantics TF in a one-on-one TelCo a week ago. However, when I now look at my notes, I’m again confused.
> 
> If I understood Enrico correctly then a referentially opaque IRI doesn’t refer to anything. However, it was my understanding of the CG report semantics that IRIs in quoted triples are interpreted, but strictly following the syntactic form. My reading of the unstar-mapping supports that intuition [1].
> To give an example, I understood referential opacity as meaning that "dbr:Linköping" and "DBR:LINKÖPING" both refer to the city of Linköping, and yet are not equal (and can not infered to be equal) because their lexical representation differs.
> But according to how I understood Enrico they don’t refer to anything.
> 
> Was I wrong all along? Am I just not getting it and does there exist a world in which both interpretations are true? Or has the TF diverged from the CG? Or is there no consensus in the TF?
> 
> 
> Best,
> Thomas
> 
> 
> 
> 
> [0] https://github.com/w3c/rdf-star-wg/wiki/Semantics%3A-Behaviour-catalogue
> [1] https://w3c.github.io/rdf-star/cg-spec/2021-12-17.html#mapping

Received on Saturday, 21 October 2023 12:22:14 UTC