Several points:
1. The definition of dwc:individualID is an identifier for "an individual or named group of individual organisms...".  Thus by this definition a small population of organisms of the same species found together can be considered an individual even if they are not biological individuals.  The definition of individual is a functional one that facilitates the common circumstance you describe where a collector collects "duplicates" that aren't really duplicate individuals but are considered to reliably be from the same species because the members of the population are in close proximity and (hopefully) the collector took care to collect only biological individuals of the same species. 
2. If it is discovered that a sheet has individuals of two species, a curator would undoubtedly create two records for the two species on the sheet.  I can't imagine the curator would try to somehow cram the metadata for the specimens of both species into the same record unless the curator had some kind of special way of dealing with "specimens" that were actually themselves collections of species.  The fact that the occurrences described in the two records were on the same piece of paper would not really be relevant other than that they would have the same collection date, collector, etc. in the same way as would two specimens of different species collected on the same day by the same collector placed on two different papers.
3. I do not see why cataloging the two different parts of the same organism as separate specimens would be any problem at all.  I've collected from the same tree in different seasons to get leafy stems and then winter twigs.  They are two dwc:Occurrences, each with its own set of metadata properties, and its own identifier that happen to be from the same individual.  People who do mark/recapture or repeated observations of live organisms have multiple Occurrences from the same individual all the time. 
4. The issue that you bring up about the problem of different determinations based on different specimens is not a problem if the determinations are associated with the individuals rather than with the Occurrences (i.e. specimens) as I suggest in the paper (see Fig. 8 on p.30).  If the assertion is made that the individual from which the first specimen is derived is owl:sameAs the individual from which the second specimen is derived, then a client capable of drawing inferences from RDF (e.g. a 'bot gleaning biodiversity metadata from many institutions to build a large database) will apply determinations linked to either of the individuals to both of them (since they are known to be the same entity).  All of the determinations applied to the (now singular) individual will be associated with both specimens through the relationship of  each specimen to its source individual (i.e. its dwc:individualID property).  Users of the resulting database would be able to examine for either specimen the entire set of determinations associated with the (formerly separate) individuals.  They could assess the temporal order of the values of the determination's dwc:dateIdentified properties (i.e. which is most "current") and assess the weight to place on a particular determination based on the identity of the determiner (dwc:identifiedBy property).  You say that the holders of the original duplicates would not be interested in the determination based on the acorn.  Really?  If the specimens and the acorn came from the same tree, the curators certainly ought to be interested because the tree couldn't simultaneously BE two different species (even if it had two determinations)!

This suggested solution isn't intended to address all kinds of associations, just the case of duplicates.  Some one else can take that one on... :-)
Steve

Bob Morris wrote: 
Good idea, but it suffers from the same fate as might
associatedOccurrences  (not previously mentioned because I was after
some clarification in principle, with the herbarium duplicate sheets
only one current case of interest): I need to follow whatever the
community practice is of regarding a sheet as part of a duplicate set
distributed by the original collector.  I'm told by the people at the
Harvard University Herbaria that "duplicate" usually, but not always,
means from the same organism and same collection event---occasionally
people used to put several organisms on the same sheet, raising the
possibility that they are not even the same taxon. Worse,  the
different parts of the same organism might be catalogued as separate
specimens. In this case, an assertion that they are from the same
individual might be true and understandable, but the utility of that
assertion depends on your purpose. Consider a use case in which one
set of traditional duplicates all have a determination that is out of
date, but another specimen---say your acorn collected later from the
same tree---has a current determination.  For purposes of notifying
duplicate holders that a new determination has been made to the
original, the later acorn may not be interesting. This means that for
this use, a distributed query of the form "find all records with the
same dwc:individualID" is not as useful as "find all records with the
same dwc:eventID".

Also, as Mark writes, it doesn't address any other associatedOccurrences.

More generally, we are working on annotations of data records.
Probably what the real issue here is that associatedOccurrences is an
assertion about organisms, and we are making assertions about
occurrence data.

On Mon, Aug 23, 2010 at 3:07 PM, Steve Baskauf
<steve.baskauf@vanderbilt.edu> wrote:
  
Bob,
It seems to me that the most semantically clear way to indicate in a
machine-readable way that two herbarium sheets are duplicates would be to
assert that they have the same dwc:individualID.  individualID is defined as
"An identifier for an individual or named group of individual organisms
represented in the Occurrence" so asserting that two occurrences represent
the same individual or named group of individual organisms pretty much
exactly describes what duplicate specimens are.  I use this same approach to
indicate that
http://bioimages.vanderbilt.edu/baskauf/67307
is an image of an acorn from the same tree:
http://bioimages.vanderbilt.edu/ind-baskauf/67304
as the bark image
http://bioimages.vanderbilt.edu/baskauf/67312
I won't say more here as I have written more extensively on this approach in
Biodiversity Informatics 7:17-44
(https://journals.ku.edu/index.php/jbi/article/view/3664).  You can also
look at the RDF associated with those GUIDs to see what I mean.  Solving
this problem is also one of the reasons I have proposed adding the class
Individual to DwC (i.e. so that the individuals that are the object of
dwc:individualID can be rdfs:type'd using a well-known vocabulary and
therefore be "understood" by linked data clients).

Steve

Bob Morris wrote:

http://rs.tdwg.org/dwc/terms/index.htm#associatedOccurrences   carries
this description:

associatedOccurrences
Identifier:	http://rs.tdwg.org/dwc/terms/associatedOccurrences
Class:	http://rs.tdwg.org/dwc/terms/Occurrence
Definition:	A list (concatenated and separated) of identifiers of
other Occurrence records and their associations to this Occurrence.
Comment:	Example: "sibling of FMNH:Mammal:1234; sibling of
FMNH:Mammal:1235". For discussion see
http://code.google.com/p/darwincore/wiki/Occurrence
Details:	associatedOccurrences

My questions:
a.  Are the names of the associations, and/or the syntax of the value
meant to be community defined?
b. If no to a. , where are those definitions? If yes, Have any
communities defined any names and syntax? I am especially interested
in "duplicate of" in the case of herbarium sheets."
c. (May share an answer with b.) Is there any use being made by anyone
in which associatedOccurrences is designed to have machine-readable
values.  If yes, where?

Thanks
Bob





--
Steven J. Baskauf, Ph.D., Senior Lecturer
Vanderbilt University Dept. of Biological Sciences

postal mail address:
VU Station B 351634
Nashville, TN  37235-1634,  U.S.A.

delivery address:
2125 Stevenson Center
1161 21st Ave., S.
Nashville, TN 37235

office: 2128 Stevenson Center
phone: (615) 343-4582,  fax: (615) 343-6707
http://bioimages.vanderbilt.edu

    



  

-- 
Steven J. Baskauf, Ph.D., Senior Lecturer
Vanderbilt University Dept. of Biological Sciences

postal mail address:
VU Station B 351634
Nashville, TN  37235-1634,  U.S.A.

delivery address:
2125 Stevenson Center
1161 21st Ave., S.
Nashville, TN 37235

office: 2128 Stevenson Center
phone: (615) 343-4582,  fax: (615) 343-6707
http://bioimages.vanderbilt.edu