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Re: RDF* vs RDF vs named graphs

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Mon, 30 Nov 2020 08:53:11 -0500
To: Miel Vander Sande <miel.vandersande@meemoo.be>, Patrick J Hayes <phayes@ihmc.us>
Cc: "public-rdf-star@w3.org" <public-rdf-star@w3.org>
Message-ID: <64456974-8f9a-1d62-9f15-9d842f906134@gmail.com>
RDF reification does have a formal semantics.  Different versions of
reification can be obtained in RDF by using the RDF reification vocabulary in
different ways.

RDF* is perhaps an attempt to pick out one possible version of RDF reification
and provide a simpler syntax for that version, either using the RDF
reification vocabulary or via some other means.  But I don't see how that
provides any extra expressive power.


It is definitely the case that RDF reification provides some things that are
not provided directly by using named graphs.   A question is whether this
extra is actually useful by itself or whether providing something useful
requires combining reified statements, in which case named graphs (or some
other formalism) is a better start.


If the main goal of this group is "to provide compatibility with the PG world"
then that needs to be clearly stated in the group's charter and examples need
to be taken from this use case.  I don't see either of these currently being
the situation.


peter




On 11/30/20 3:48 AM, Miel Vander Sande wrote:
> Just like RDF reification, named graphs have been around without formal
> semantics. We have an attempt at the former with RDF*. Including the latter
> is a question of scoping and there is nothing that prevents anyone to take a
> crack at the latter. TBH, I think this fits in the scope of what the N3
> group is doing and they are making efforts to harmonize with RDF*. In the
> meantime, you can still use the current Named Graphs as you see fit (see
> also Olaf's answer to Martynas). For me, describing a statement directly
> (RDF*) is significantly different from describing an identifier which is
> "somehow" related to a set of statements (Named Graph). I would like to know
> what this "somehow" relation means if I'm migrating a dataset full of NG's
> to another system. 
>
> I appreciate the work this group is doing in terms of making the
> interpretation of reification clear and usable. Its main goal is still to
> provide compatibility with the PG world, where properties over a group of
> edges simply doesn't exist. I think this limited scope actually helps
> getting somewhere within reasonable time. 
>
> Best,
>
> Miel
>
> Op ma 30 nov. 2020 om 01:43 schreef Patrick J Hayes <phayes@ihmc.us
> <mailto:phayes@ihmc.us>>:
>
>     I agree. When I first met the idea of RDF* I made this same point to
>     Thomas, and we had some correspondence on the topic. I came to the
>     conclusion that my expending effort towards the development of RDF*
>     would be a waste of time.
>
>     Pat
>
>     > On Nov 29, 2020, at 4:43 PM, Peter F. Patel-Schneider
>     <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>> wrote:
>     >
>     > I've been thinking about the expressive power of RDF* related to the
>     > expressive power of RDF, at least the versions of RDF* that have been
>     proposed
>     > so far.
>     >
>     > As far as I can tell anything that can be done in RDF* can be easily
>     done in
>     > RDF by using standard
>     > RDF reification techniques, perhaps slightly modified (e.g., to
>     account for
>     > malformed literals), with extra properties linking to syntactic
>     encodings to
>     > achieve referential opacity.
>     >
>     > But named graphs are more expressive than RDF* in a certain sense, as
>     named
>     > graphs allow multiple "embedded" triples to be collected together.
>     >
>     >
>     >
>     > peter
>     >
>     >
>     >
>
>
Received on Monday, 30 November 2020 13:53:25 UTC

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