Re: RDF-ISSUE-25 (Deprecate Reification): Should we deprecate (RDF 2004) reification? [Cleanup tasks]

On Thu, 2011-04-07 at 20:43 -0400, Eric Prud'hommeaux wrote:
> * Sandro Hawke <sandro@w3.org> [2011-04-07 18:23-0400]
> > On Thu, 2011-04-07 at 18:18 -0400, David Wood wrote:
> > > On Apr 7, 2011, at 18:07, RDF Working Group Issue Tracker <sysbot+tracker@w3.org> wrote:
> > > 
> > > > 
> > > > RDF-ISSUE-25 (Deprecate Reification): Should we deprecate (RDF 2004) reification? [Cleanup tasks]
> > > > 
> > > > http://www.w3.org/2011/rdf-wg/track/issues/25
> > > > 
> > > > Raised by: Sandro Hawke
> > > > On product: Cleanup tasks
> > > > 
> > > > 
> > > > The RDF 1999 and 2004 Recommendations include vocabulary and syntax
> > > > (in RDF/XML) for RDF "reification".  The vocabulary is rdf:Statement,
> > > > rdf:subject, rdf:predicate, and rdf:object; the syntax is rdf:ID used
> > > > on a property element.
> > > > 
> > > > Although this feature is sometimes used in practice, some experts
> > > > advise data providers to avoid it.  It has no syntactic support in
> > > > RDFa or Turtle.  Should the WG align with this advice and say this
> > > > feature is only to be use for backward compatibility?  (That is,
> > > > RDF/XML parsers must continue to support the syntax, and libraries
> > > > should allow applications to use the features to interoperate with
> > > > legacy RDF systems.)
> > > > 
> > > > Note that many or all of the use cases of reification are also uses
> > > > cases for [GRAPHS].  The decision about the fate of reificiation is
> > > > connected with what happens with [GRAPHS].
> > > 
> > > 
> > > Might reification undergo a renaissance when provenance comes back into fashion?  Couldn't we consider reification a degenerate case of a named graph?
> > > 
> > > We might want to go slowly on this one...
> > 
> > I think it's one of the candidate solutions for the GRAPHS use cases.
> > My guess is it's unlikely to survive, but who knows.  :-)
> > 
> > Maybe I should move it from [Cleanup tasks] to [GRAPHS] ?
> 
> People objected to reification for inference and syntax reasons.
> 
> INFERENCE
> The inference issues boil down to the fact that rules applicable to a
> flat graph must be transformed when applied to a reified graph. The
> principle exemplar being owl:sameAs:
>   <LoisLane> <says> [ rdf:s <Superman> ; rdf:p <can> ; rdf:o <fly> ] .
>   <Superman> owl:sameAs <ClarkKent> .
> Applying the sameAs to the reified graph tells you that Lois Lane says
> that Clark Kent can fly, just as it would if you applied it to all
> symbols in
>   <SYSTEM> { <LoisLane> <uttered> <G1> . }
>   <G1> { <Superman> <can> <fly> . }
> 
> If we want use graphs for quoting, we have to be judicious about the
> application of sameAs. Perhaps we want our <SYSTEM> to infer that if
>   <Superman> <canBeatUp> <LexLuther> .
> then
>   <ClarkKen> <canBeatUp> <LexLuther> .
> Of course, we can be equally judicious about the application of sameAs
> in the reified world, using a rule like:
>   { ?X owl:sameAs ?Y .
>     <SYSTEM> <holds> [ rdf:s ?X ; rdf:p ?p ; rdf:o ?o ] . }
>   => 
>   { <SYSTEM> <holds> [ rdf:s ?Y ; rdf:p ?p ; rdf:o ?o ] . }
> 
> In short, I'm not convinced that named graphs offers any more quoting
> ability than reification. We just can't mix reified and non-reified
> statements. (More precisely, we need to know which statements are
> reified, much as we need to know if an statement is inside {}s.)
> 
> 
> SYNTAX
> We can define a predicate <uttered> to encode quoting in named graphs:
>   uttered: asserts that the subject asserted all of the statements
>            in the graph named in the object.
>   <SYSTEM> { <LoisLane> <uttered> <G1> .
>              <Superman> <canBeatUp> <LexLuther> .}
>   <G1> { <Superman> <can> <fly> . }
> or reification:
>   uttered: asserts that the subject asserted the dereification of the
>            objects of the <holds> arc from the object. [wordsmithing opportunity]
>   <SYSTEM> <holds> [ rdf:s <LoisLane> ; rdf:p <uttered> ; rdf:o <G1> ] ,
>                    [ rdf:s <Superman> ; rdf:p <canBeatUp> ; rdf:o <LexLuther> ] .
>   <G1> <holds> [ rdf:s <Superman> ; rdf:p <can> ; rdf:o <fly> ] .
> or more simply in N3:
>   uttered: asserts that the subject asserted the statements in the object.
>   <SYSTEM> <holds> { <LoisLane> <uttered> { <Superman> <can> <fly> . } .
>                      <Superman> <canBeatUp> <LexLuther> . } .
> 
> What happens when Lois says that Lex says that Superman can fly?
> name graphs:
>   <SYSTEM> { <LoisLane> <uttered> <G1> .
>              <Superman> <canBeatUp> <LexLuther> . }
>   <G1> { <LexLuther> <uttered> <G2> . }
>   <G2> { <Superman> <can> <fly> . }
> reification:
>   <SYSTEM> <holds> [ rdf:s <LoisLane> ; rdf:p <uttered> ; rdf:o <G1> ] ,
>                    [ rdf:s <Superman> ; rdf:p <canBeatUp> ; rdf:o <LexLuther> ] .
>   <G1> <holds> [ rdf:s <LexLuther> ; rdf:p <uttered> ; rdf:o <G2> ] .
>   <G2> <holds> [ rdf:s <Superman> ; rdf:p <can> ; rdf:o <fly> ] .
> n3:
>   <SYSTEM> <holds> {
>     <LoisLane> <uttered> {
>       <LexLuther> <uttered>  {
>         <Superman> <can> <fly> . } . } .
>     <Superman> <canBeatUp> <LexLuther> . }
> 
> SPARQL syntax might lead us to believe that queries can use nesting to
> match she-said-he-said quotes, but I don't think there's any distinction
> between (here arbitrarily promoting <SYSTEM> to the default graph):
>   ASK {
>     ?she <uttered> ?g1
>     GRAPH ?g1 {
>       ?he <uttered> ?g2
>       GRAPH ?g2 {
>         <Superman> <can> <fly>
>       }
>     }
>   }
> and
>   ASK {
>     ?she <uttered> ?g1
>     GRAPH ?g1 {
>       ?he <uttered> ?g2
>     }
>     GRAPH ?g2 {
>       <Superman> <can> <fly>
>     }
>   }
> 
> The real challenge for named graphs comes when we don't have names for
> our speach acts. Reification causes no problem:
>   <SYSTEM> <holds> [ rdf:s <LoisLane> ; rdf:p <uttered> ; rdf:o _:g1 ] .
>   _:g1 <holds> [ rdf:s <LexLuther> ; rdf:p <uttered> ; rdf:o _:g2 ] .
> but names graphs requires bnode scope to escape the graph boundries:
>   <SYSTEM> { <LoisLane> <uttered> _:g1 . }
>   _:g1 { <LexLuther> <uttered> _:g2 . }
> Critics of bnodes will no doubt say "invent names for your speach acts",
> but "honor the names you invented" is a pretty heavy burden compared to
> having to write out reification.

Are you saying the rdf Reification is a good solution to the [GRAPHS]
use cases?   It sounds like it.

     -- Sandro

Received on Friday, 8 April 2011 01:04:26 UTC