Statements about statements -- Help needed!

In working on the XSLT transform to convert NewsML 2 [1] metadata 
to RDF, we're having problems with statements about statements.  We 
would appreciate advice, especially if it is couched in terms we can 
A NewsML metadata element can take as a value one of the following:
-  a concept, represented by a CURIE [2]
-  a string
-  a structured element, eg one describing a person or an 
-  an rdf:bag containing elements whose values are taken from the 
   above list
The metadata element typicaly relates the value to a news item, eg:
-  a creator|contributor|subject|genre|etc of news item X is Y
NewsML 2 allows one to make a number of additional statements.  Some 
of these are about the value itself; others are about the assignment 
of the value.
The first category hasn't caused us problems.  Examples of such 
statements are:
-  concept X is of type Y
-  concept X is the same concept as concept Y
-  concept X is the child of concept Y
-  the title (aka label) of concept X is the string "Y"
It is the second category that is causing us problems.  It includes 
statements such as:
-  this statement was created by A
-  this statement was created on date/time B
-  this statement was made with confidence level C
-  the relevance level of this statement to the news item is D
-  this statement is based on information derived by method E
We've studied the RDF Primer [3], especially section 4.3 RDF 
Reification [4] and the description given there highlights a number 
of problems.  For example, there does not appear to be any way, 
within an RDF graph, to identify a specific instance of a triple.
So it seems that we couldn't express:
-   Fred said on 22 Dec 2005, with a confidence of 40%, that 
    a subject of this news item is concept X.
The section seems to offer two semi-viable options:
-  Use rdf:ID to identify a statement and then make statements about 
   the identified statement.
-  Use some other, application-specific, way to identify statements 
   but then don't expect anyone else to understand it.
We're not clear how either of these would be represented in the 
various triples notations and we're not sure which path to follow.
Any advice would be gratefully received, especially if reading it 
does not require the consumption of large quantities of headache 

Misha Wolf
News Standards Manager, Reuters,
Chair, News Metadata Framework WG, IPTC,
Vice-Chair, NewsML 2 Architecture WP, IPTC,

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Received on Thursday, 22 December 2005 17:27:43 UTC