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Re: [issue needed] Re: RDFCore last call WD's: Two comments on the RDF documents

From: Bob MacGregor <macgregor@ISI.EDU>
Date: Thu, 27 Feb 2003 17:36:19 -0800
Message-Id: <5.1.1.6.0.20030227173349.00ba81d0@tnt.isi.edu>
To: Brian McBride <bwm@hplb.hpl.hp.com>, fmanola@mitre.org
Cc: www-rdf-comments@w3.org

Brian,

At 10:35 PM 2/27/2003 +0000, Brian McBride wrote:
>At 13:31 27/02/2003 -0800, Bob MacGregor wrote:
>
>>Hi Frank,
>>
>>Currently, only you and Pat Hayes have responded (back to me) to the
>>comments that I posted earlier to RDF-comments,
>
>Bob, I hope you don't think that is a bad thing.  The editors of each 
>document are handling the comments on their documents.  Please don't 
>expect the entire WG to join you in debate.

Having everyone chime in would not be a good thing.  I was not suggesting 
that I
should have had more responses, but I was hoping that to have gotten
a response about each issue that I raised.  Below, I mention the two 
unanwered issues


>>  and those responses did not
>>include consideration of some of the issues I raised.
>
>That is a matter of concern to me.  It is our intent to ensure that each 
>issue is properly addressed.  Can I assume that any issues that you feel 
>have not been addressed are captured in this message, or are there others 
>you can refer me to?

One issue was the discussion surrounding the example
  "I don't believe that George is a clown" in the Concepts
and Abstract Syntax document,  the larger issue being
whether or not propositional attitudes are or should be expressible.
The (non-RDF) nested syntax in the Primer relates to the same issue
(but Frank has already replied to me about the Primer).

The second issue is the question of unasserted forms/statements.

I am unable to find an RDF example of how to represent
a statement of belief (a propositional attitude).  Neither can
I find an example showing exactly what is meant by an
unasserted RDF statement. (If there are examples, they are not
identified as such.  Or I somehow missed them).

These are what I referred to as unanwered issues.  I'm hoping that
someone will tell me what the "official" position is.
My last e-mail summarized my position
as to these two issues, so I won't go any deeper here.


>We are a bit behind the schedule that I hoped we would meet.  It was my 
>hope that we would have captured all outstanding comments in our comments 
>tracking document by Friday so I could send out a 'sweeper' message ("We 
>think we've got all the issues recorded- if we missed one, please shout"), 
>but we aren't there yet :(
>
>Brian
>
>>   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
>>that aren't going to yield, so I've pretty much dropped the
>>discussion.  However, if you indeed can create a new issue out
>>of this, that would be a good thing.  Below, I've summarized my
>>impression of the body of issues related to reification in RDF.
>>
>>Below, I first pose some of the key questions; then I summarize
>>my take on the status of reification in RDF; then I provide my
>>answers to each of the questions; and finally I make some
>>summary recommendations.
>>
>>1. Should RDF be able to represent statements about statements?
>>2. Does the current RDF support statements about statements?
>>
>>For each of 1 and 2, what kind of semantics do we have in mind:
>>     3. Should/can RDF express propositional attitudes?
>>     4. Should/can RDF express provenance information about statements?
>>
>>First, some background remarks:
>>
>>  Propositional attitudes:
>>    The semantics are very hard to pin down here.  It is hard to
>>    imagine the WG reaching agreement on what they are in this
>>    go-round (if ever).  So, while I was arguing for their inclusion
>>    in RDF a while back, it seems pretty clear that they are not a part
>>    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
>>    to support them.  HOWEVER, there is a big hole in the current
>>    RDF support for provenance information:
>>
>>    Suppose I wish to make a statement that John is the author of
>>    a statement [S P O].  I can write something like:
>>
>>      S1 type ReifiedStatement.
>>      S1 subject S.
>>      S1 predicate P.
>>      S1 object O.
>>      S1 dc:creator John.
>>
>>    Support there are two different graphs G1 and G2 that both contain
>>    statements with values S,P,O.  Which one is John the author
>>    of, i.e., which one does S1 refer to? We have no idea, because
>>    RDF makes no provisions for identifying which among a set of
>>    statements a reified statement refers to.
>>
>>    Is this easy to fix?  Unfortunately, in order to select among
>>    a set of graphs, we run into another open RDF issue, which is
>>    roughly phrased as "Does a URI that matches an RDF file URI
>>    denote the document or the graph within it?".  Resolving that
>>    that issue might be regarded as a prerequisite to resolving the
>>    provenance issue.  Perhaps a resolution of the issue of "contexts"
>>    is also a prerequisite.  In any event, there is at present no means
>>    for creating a URI that denotes an RDF graph.
>>
>>Back to the original question.  My impression is that there is a 
>>(non-explicit)
>>consensus within the WG that the current RDF cannot represent
>>propositional attitudes, i.e., the answer to
>>question 3 above is "No".  Can RDF represent provenance information
>>(question 4)?  I claim that RDF provides some very simple (and
>>non-controversial) hooks (the subject, predicate, object properties)
>>and omits a key notion (the ability to refer to a graph) that is
>>needed to make the whole provenance notion workable.  So, while
>>from a mathematical standpoint the answer to question 4 might be
>>"Yes", from a PRAGMATIC standpoint, the answer is "No".
>>
>>If one agrees that the answers to questions 3 and 4 are "No" and
>>"No", then the answer to question 2 is probably "No" also.
>>
>>Hence, one possible recommendation (which I posited in an earlier
>>e-mail) is to drop the entire notion of reification from RDF.  However,
>>it seems pretty clear that this is a non-starter.  Hence, I have
>>some alternative recommendations.
>>
>>Recommendations:
>>
>>   We probably want RDF to support representation of provenance information.
>>   There ought to be an open issue in one of the RDF documents that states
>>   roughly "RDF currently does NOT provide adequate support for
>>   provenance information, but it may in the future."
>>
>>   Propositional attitudes are probably out of bounds.  In that case,
>>   this should be made clear in the documents.  Right now the
>>   "I don't believe that George is a clown" discussion leaves the
>>   impression that this kind of propositional attitude is something
>>   that we can say in RDF.  I recommend eliminating this from the
>>   Concepts and Abstract Syntax document.  The (non-RDF) example
>>   of a nested statement in the Primer further contributes to such an
>>   impression.  I recommend rewording that example (Frank has already
>>   acknowledged this latter comment).
>>
>>   Asserted and non-asserted forms:  The RDF documents do not include
>>   any example of a graph that contains both asserted and non-asserted
>>   RDF statements, unless one counts reified statements as providing
>>   an example of (possily) unasserted statements.  If that is what is
>>   meant, then this should be stated plainly.  If some other notion
>>   (that I can't guess at) is meant, then that should be stated plainly.
>>   Otherwise, the entire section on asserted and unasserted forms
>>   should be eliminated.
>>
>>Cheers, Bob
>>
>>Ironic note: Because we need to represent provenance information in some
>>of our RDF applications, and because its not currently supported,
>>we had to look for other ways to make things work.  We have invented
>>a variant form of context that solves our problem, AND, we like
>>that solution much better than the reified statement solution.  So,
>>if an RDF WG ever fixes reification, we probably won't use it anyway.
>>
>>
>>At 04:10 PM 2/26/2003 -0500, Frank Manola wrote:
>>>Brian--
>>>
>>>Can I have an issue for this please?  Basically I'm raising this (or at
>>>least the part about the Primer;  the message also has a comment about
>>>Concepts) to the WG level because I need input from the WG (especially
>>>Pat, but others may have opinions as well) on how we should handle these
>>>comments about reification.  Pat and I need to be in synch on this in
>>>order to also deal with Bob's comments on the Semantics document in
>>>http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0211.html,
>>>and we also have issue danc-03 raised in
>>>http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0218.html
>>>that suggests deleting the Primer reification section entirely.  And I
>>>recall some messages from Pat about "propositional attitudes" (I can't
>>>recall the thread right now) that are pertinent to Bob's comments.
>>>
>>>--Frank
>>>
>>>Bob MacGregor wrote:
>>> >
>>> > Frank,
>>> >
>>> > At 03:04 PM 2/13/2003 -0500, Frank Manola wrote:
>>> > > >
>>> > >snip
>>> > > >
>>> > > > So, how am I recommending that you fix things?  Unfortunately, 
>>> I'm mostly
>>> > > > stating what you should NOT do.  I'm claiming that
>>> > > > using nested syntax will convey the wrong impression to many 
>>> readers (e.g.,
>>> > > > those that model belief they way I did above), so something like an
>>> > > > EXPLICIT quotation needs to be included.  To me, the use of 
>>> double brackets
>>> > > > didn't adequately convey the notion of quotation.
>>> > > >
>>> > >snip
>>> > >
>>> > >I will try using a diagram, rather than what appears to be nested
>>> > >syntax, since we don't support nested syntax (and I didn't intend for
>>> > >what the Primer uses to be interpreted as nested syntax). However, we
>>> > >don't really support explicit quotation either, so we can't really
>>> > >substitute that.  Whatever is said in the Primer on reification will
>>> > >have to be consistent with what is said in the Semantics document, which
>>> > >means this is related to your message
>>> > >http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0211. 
>>> html
>>> > >"Statings -- Much ado about nothing".
>>> >
>>> > I agree that figuring out a representation is tough.  I'm used to 
>>> KIF, where
>>> > I can say pretty much anything that I want to.  Its hard even to have an
>>> > e-mail conversation about certain aspects of RDF, since the 
>>> vocabulary just
>>> > isn't available.
>>> >
>>> > > > I consider introducing "what we would *like* to be able to do" very
>>> > > > dangerous.  It
>>> > > > gives the impression that RDF might be used to represent 
>>> propositional
>>> > > > attitudes,
>>> > > > when in fact it can't.  I would prefer that the WG be as up front as
>>> > > > possible about
>>> > > > stating the limitations it has placed on RDF.
>>> > >
>>> > >I don't think the Primer actually conveys this impression, and I think
>>> > >it tries to be up front about the limitations of RDF reification (it
>>> > >certainly spends a lot of space talking about them at any rate).
>>> > >However, I could see adding a caveat at the beginning along the lines of
>>> > >"you might think you're going to be able to do foo, but watch carefully,
>>> > >because you can't".  Does this make sense?
>>> >
>>> > Yes.  Again, we have a vocabulary problem.  I've seen the phrase 
>>> "propositional
>>> > attitude" pop up now and again, but the notion of "proposition" is quite
>>> > difficult
>>> > to pin down, so that makes it hard to discuss.  But, I will try.
>>> >
>>> > I think of propositions as being the proper objects of belief.  So, 
>>> one doesn't
>>> > believe in a *sentence* "George is a clown".  Rather, one believes in the
>>> > proposition
>>> > that that sentence is true.  In KIF, I'm used to seeing nested syntax
>>> > employed when
>>> > representing statements about belief.  Thus, if RDF allowed nested
>>> > statements, then
>>> > I would use them to represent belief.  But it doesn't, and hence I'm 
>>> thinking
>>> > that an example that *does* employ nesting gives the wrong impression.
>>> >
>>> > However, the following text appears in the Concepts and
>>> > Abstract Syntax document:
>>> >
>>> >     > Not every RDF/XML expression is asserted. Some may convey meaning
>>> > that is partly
>>> >     > determined by the circumstances in which they are used. For 
>>> example,
>>> > in English, a
>>> >     > statement "I don't believe that George is a clown" contains the 
>>> words
>>> > "George is a clown",
>>> >     > which, considered in isolation, has the form of an assertion that
>>> > George exhibits certain
>>> >     > comic qualities. However, considering the whole sentence, no such
>>> > assertion is considered
>>> >     >to be made.
>>> >
>>> > I'm still waiting to see an example of an RDF statement that is not
>>> > asserted.  If someone
>>> > could illustrate one, that would be a big help.  If, in fact this passage
>>> > is meant to
>>> > refer to reified statements, then please write down how this would 
>>> look in
>>> > RDF using reified
>>> > statements.
>>> >
>>> > Note: The text above actually uses term "expression" rather than
>>> > "statement" when it
>>> > talks about things being asserted.  RDF terms are expressions, and 
>>> terms cannot
>>> > be asserted, so that makes the
>>> > first sentence trivially true.  But I assume that that was not the 
>>> authors'
>>> > intent.
>>> > Suggestion: Replace "expression" by "statement" in the first sentence, if
>>> > that's what's
>>> > meant.
>>> >
>>> > My impression is that its impossible to express the sentence
>>> >       "I don't believe that George is a clown"
>>> > in RDF.  In the OLD RDF, I would have said yes, but not now that we have
>>> > switched
>>> > to "statings".  If it is acceptable for a stating to serve as the 
>>> object of
>>> > a statement
>>> > about belief, then I would have to withdraw my objection.  So, can we 
>>> represent
>>> > beliefs in RDF?
>>> >
>>> > Cheers, Bob
>>>
>>>--
>>>Frank Manola                   The MITRE Corporation
>>>202 Burlington Road, MS A345   Bedford, MA 01730-1420
>>>mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-8752
>>
>>Robert MacGregor
>>Project Leader
>>USC Information Sciences Institute
>>4676 Admiralty Way, Marina del Rey, CA 90292
>>macgregor@isi.edu
>>Phone: 310/448-8423, Fax: 310/822-6592
>>Mobile: 310/251-8488

Robert MacGregor
Project Leader
USC Information Sciences Institute
4676 Admiralty Way, Marina del Rey, CA 90292
macgregor@isi.edu
Phone: 310/448-8423, Fax: 310/822-6592
Mobile: 310/251-8488
Received on Thursday, 27 February 2003 20:36:40 GMT

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