RE: use/mention and reification: rdf:predicate/subject/object [was: RDF Abstract Syntax...]

Graham Klyne wrote:
> ...
>
> And some personal thoughts about your proposed representation:
>
> I cannot help wondering if it has gone too far in the opposite
> direction.  In my musings about statements and contexts [1], I
> settled on a
> quadruple-based structure (different from the CWM structure you
> describe),
> which (in some interpretations) would treat <id,p,s,o> as a
> reification of
> a statement '(s p o)' with identifier 'id'.  I find that, with additional
> RDF properties (and associated semantics), this seems to be capable of
> capturing the important aspects of the expression you mention,

Right, the (p,s,o,context) quad has been used for decades (e.g. Grasper
http://www.ai.sri.com/~grasper/), in your paper as well as TimBL's.

>... thus:
>
> You propose a Statement is represented by the 7-tuple:
>    <predicate,subject,object, contextURI,id, index, asserted>
>
> Your 'ContextURI'+'id' serve the same purpose as my id.  reserving the
> components of a QName structure has some appeal, but I'm not clear if it
> needs to be done at this level.

Sure. One can similarly debate/discuss whether the predicate,subject,object
might be best represented as a QName e.g. <namespace URI, localname> pair.

>
> Your 'index' is to do with preserving information about lexical
> ordering of
> statements.  I have serious doubts that this has a place in the RDF
> r5epresentation:  either the ordering is significant in which case it
> should be captured in the RDF graph, or it is not.

I would like to see another proposal to implement containers, particularly
rdf:Seq. I, and numerous others, find the current syntactic contortion of
<rdf:li> -> rdf:_1 painful. The entire treatment of containers a mess badly
in need of fixing.

It turns out that lexical ordering already _has_ a place in RDF, my proposal
is an attempt to fix the current problem.


> (I note the arguments
> that order is "semi-significant", but do not think that these justify
> complicating the core RDF structure.  Individual applications are free to
> preserve additional information as they see fit.)

If an individual application is _free to preserve_, this information
_should_ be in the abstract syntax, else different applications will use
different abstract syntaxes, rendering the RDF well, confusing.

>
> Your 'asserted' property is captured in my framework by an explicit
> property linking the context in which the statement is asserted to the
> reified statement.  Thus, an asserted statement needs two tuples:  one to
> describe the statement, and one do describe its assertion.  I am
> comfortable with the additional tuple required;  for some purposes (e.g.
> mine!) I feel it is more expressive.

Not two extra statements: 5, one to describe assertion and 4 for
reification. A single property seems a worthy tradeoff to reduce the number
of statements by a factor of 5.

-Jonathan

Received on Sunday, 27 May 2001 14:03:51 UTC