W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > June 2001

Re: Abstract syntax: an attempt

From: pat hayes <phayes@ai.uwf.edu>
Date: Sat, 23 Jun 2001 23:25:44 -0500
Message-Id: <v0421010bb75a4ba2948f@[205.160.76.176]>
To: Sergey Melnik <melnik@db.stanford.edu>
Cc: w3c-rdfcore-wg@w3.org
>Brian,
>
>I'd just like to reiterate some of the arguments for making reification
>a built-in feature (possibly as an optional layer):
>
>- in M&S, reified statements need to have a URI. It looks like they
>should be unique, but nobody wants to deal with uniqueness, but still
>some sort of URIs need to be assigned, so we end up having to deal with
>different URIs denoting the same statement etc.
>
>- in M&S, we need a specific vocabulary to express/use reification.
>Reification could be defined without relying on vocabularies.

Im not sure that makes sense. Quotation, or something similar, could 
be defined without vocabularies, indeed (you just need a quotation 
syntax), but quotation alone doesn't really give you the full power 
of reification, since it provides no way to reason about the reified 
statement: all you can do is to exhibit it, you can't get at its 
'parts' without some kind of particular meta-language vocabulary.

>- as defined in M&S, reification is extremely verbose and clumsy both in
>APIs and in the syntax,

Well, the XML syntax for RDF is all extremely verbose and clumsy, so...?

>and very few people are using it as suggested.
>However, I personally believe it is a useful feature when introduced
>correctly and compactly, and it can be easily handled in APIs and
>databases as an intrinsic model feature.
>
>Finally, (s1 p1 (s2 p2 o2)) looks nicer in the abstract syntax...

True, but don't get that confused with (s1 p1 '(s2 p2 o2)). (Is the 
inner triple mentioned or used? Reified or a subexpression?)

Pat Hayes

>
>Sergey
>
>
>Brian McBride wrote:
> >
> > Hi Graham,
> >
> > Thanks for this.  One question:
> >
> > Graham Klyne wrote:
> >
> > >
> > > NOTE:  "reification" is deliberately called out as a distinct syntax
> > > production, so that there is a place to hang the semantics that 
>distinguish
> > > it from any other collection of facts.  There is some syntactic ambiguity
> > > here that needs to be resolved at some level;  e.g. adjusting 
>the abstract
> > > syntax so that rdf:subject, rdf:object, rdf:predicate can 
>appear *only* in
> > > a production for R (and not for A).
> >
> > In M&S 1.0 the statements of a reification (i.e. the rdf:type, rdf:subject,
> > etc ...) are no different from other statements.  What difference are
> > you considering introducing here?
> >
> > Brian

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Received on Monday, 25 June 2001 10:43:43 EDT

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