


From: Frank Manola <fmanola@mitre.org>
Date: Thu, 27 Feb 2003 19:15:07 -0500
Message-ID: <3E5EAA0B.3010503@mitre.org>
To: Bob MacGregor <macgregor@isi.edu>
CC: www-rdf-comments@w3.org, macgreg@isi.edu


This last message of yours summarizing the situation helps a lot to 
clarify things, in my opinion.  First of all, you should understand that 
all this messaging is part of a process, which says that either we as 
individual editors decide we can handle an issue as a simple editorial 
change to our individual documents, or we have to refer it to the 
working group as an "issue".  That's what I requested be done with the 
issues you'd raised about reification, for the reasons I mentioned in my 
message.  The process is designed to explicitly respond to comments, and 
make sure to deal with them in some kind of structured manner.  So we 
couldn't really "drop" anything from our end unless you agreed to "drop" 
it too.  In other words, I wasn't trying to raise a new issue, I was 
trying to resolve an old one, by saying the working group needed to 
decide how to handle this.

Speaking for myself, my summary reply to your summary analysis is 
something like this:

1.  I agree 100% with you about the difficulty of the semantics of 
propositional attitudes.  You can, of course, write triples with 
something like ex:believes as the predicate, but that's not the same 
thing.  We're not going to get into those semantics.

2.  I agree with you about the the problem with provenance, i.e., the 
inability (at least, in terms of a built-in RDF facility) to explicitly 
identify specific statements.  Of course, if you (externally to RDF) 
have a way of assigning URIrefs to individual RDF statements, everything 
is cool. (See below for more on this).

3.  We don't explicitly say that we don't support propositional 
attitudes.  To do that, we may have to explain what the problem is 
(e.g., why the semantics of a predicate like ex:believes are hard to pin 
down), which could get a bit complicated.  As far as the Primer is 
concerned, I've thought about adding a short bit about this (basically 
saying these things are propositional attitudes, they're complicated, 
and go off and read the following references to see why).

***Do you think that type of material on propositional attitudes is 
absolutely necessary in the Primer?***  (Alternatively, how bad would it 
be if the Primer didn't cover that?) Note that I'm speaking just for the 
Primer.  If you think this needs to be explicitly mentioned in any other 
document, you probably should explicitly indicate that/those other 

4. Regarding provenance, I'm a little confused.  The whole last half of 
the Primer section on reification basically says exactly what you've 
said;  that the reificiation mechanism per se has no way of identifying 
the individual triples it describes.  There is, for example, a paragraph 
starting "This does not mean that such 'provenance' information cannot 
be expressed in RDF, just that it cannot be done using only the meaning 
RDF associates with the reification vocabulary."  It does on to explain 
that if you have a way of assigning URIs to individual statements, you 
can make statements about those statements without needing to use 
reification at all.

The point here is that RDF as we started working on it had a reification 
vocabulary with multiple interpretations.  We decided not to change the 
vocabulary this go-round (too many different views of what was wanted, 
possibly outside our charter as requiring too extensive a fix), and 
we're reporting on the appropriate interpretation of what's there.  Note 
that we can't just drop reification.  My organization, for one, has 
people using it (that is, they defined a way to assign URIs to 
statements, and use the reification vocabulary to describe the 

   My confusion boils down to this (to try to nail things down *very 
precisely*):  are you saying the Primer:

a.  doesn't explicitly say that you can't really do provenance with only 
the built-in facilities in RDF?  (I sure think it does)

b.  isn't clear enough about this? (I thought at least the paragraph I 
mentioned above, and the surrounding text, was pretty clear)

c.  doesn't say why reification is still in RDF, even though it doesn't 
do provenance the way some people thought it did?  (The Primer doesn't 
talk about that, and I'm not sure it should.  We're trying to describe 
the facilities of a specific language, not why the language isn't some 
other language.)

Given your choice of zero, one, or more of a, b, and c above, what 
specifically would you like changed in the Primer?

Again, thanks for the comments.  This last message was very helpful (at 
least to me).


PS:  I'm still going to change the "apparent nested statement" example 
in the Primer as we've discussed already.

Bob MacGregor wrote:

> Hi Frank,
> comments that I posted earlier to RDF-comments, and those responses did not
> include consideration of some of the issues I raised.  The
> discussions with Pat made it clear that the WG charter imposes
> constraints that IMHO preclude a satisfactory resolution of the
> reification issue. I don't want to tilt endlessly at windmills
> summary recommendations.
> 2. Does the current RDF support statements about statements?
>     3. Should/can RDF express propositional attitudes?
> First, some background remarks:
>  Propositional attitudes:
>    imagine the WG reaching agreement on what they are in this
>    of RDF now (and perhaps forever).
>  Provenance information:
>    The semantics here are much more tractable, both from what
>    is meant, and what adjustments are needed in the language
>    RDF support for provenance information:
>      S1 type ReifiedStatement.
>      S1 subject S.
>      S1 predicate P.
>      S1 object O.
>      S1 dc:creator John.
>    RDF makes no provisions for identifying which among a set of
>    statements a reified statement refers to.
>    that issue might be regarded as a prerequisite to resolving the
>    for creating a URI that denotes an RDF graph.
> (non-explicit)
> consensus within the WG that the current RDF cannot represent
> propositional attitudes, i.e., the answer to
> from a mathematical standpoint the answer to question 4 might be
> some alternative recommendations.
> Recommendations:
>   We probably want RDF to support representation of provenance information.
>   roughly "RDF currently does NOT provide adequate support for
>   provenance information, but it may in the future."
>   impression that this kind of propositional attitude is something
>   impression.  I recommend rewording that example (Frank has already
>   acknowledged this latter comment).
>   RDF statements, unless one counts reified statements as providing
>   Otherwise, the entire section on asserted and unasserted forms
>   should be eliminated.
> Cheers, Bob

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
Received on Thursday, 27 February 2003 18:55:22 GMT
