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<p class="MsoNormal"><o:p></o:p>I have had several off-list email
exchanges about this topic
and have been encouraged to bring the topic to this list for comment.<span
style=""> </span>Along with addressing this topic
specifically, I'd like to include clarification of how I view
Occurrences, based
partly on emails written during the October/November tdwg-content list
discussion regarding the conflict between Darwin Core and Dublin Core
usage of
dcterms:type, partly on some off-list email discussions about various
DwC terms
and their appropriate application, and partly on my own view of the
relationship between Occurrences and the proposed Darwin Core class
Individual.<span style=""> </span>If I have misrepresented anything,
please
reply to the list with your perspective on the situation.<span style="">
</span>(The following namespaces are used for brevity:
dcterms=<a class="moz-txt-link-rfc2396E" href="http://purl.org/dc/terms/">"http://purl.org/dc/terms/"</a>,<span style="">
</span>dcmitype=<a class="moz-txt-link-rfc2396E" href="http://purl.org/dc/dcmitype/">"http://purl.org/dc/dcmitype/"</a>,
dwc=<a class="moz-txt-link-rfc2396E" href="http://rs.tdwg.org/dwc/terms/">"http://rs.tdwg.org/dwc/terms/"</a>,
and dwctype=<a class="moz-txt-link-rfc2396E" href="http://rs.tdwg.org/dwc/dwctype/">"http://rs.tdwg.org/dwc/dwctype/"</a>.)<o:p><br>
</o:p></p>
<p class="MsoNormal">A. CHARACTERISTICS OF MEMBERS OF THE CLASS
dwc:Occurrence</p>
<p class="MsoNormal">1. Instances of the DwC class Occurrence represent
evidence
that a particular organism existed at some point in time.<span style="">
</span>Thus a photo of a certain bird would qualify
as an Occurrence, while a painting that was made by looking at a number
of
stuffed and live birds (but no particular one bird) would not be an
Occurrence.<span style=""> </span></p>
<p class="MsoNormal">2. Categorization of a resource as an Occurrence
does not
imply fitness of use for any particular purpose.<span style=""> </span>An
Occurrence may or may not be useful for
any of the following purposes: <span style=""> </span>serve to
document the presence of an organism in nature at a particular place
and time
(i.e. to help model the natural distribution of a species), serve as a
teaching
tool, facilitate an identification key, illustrate a character state,
provide
an image for a trademark of the museum, etc.<span style="">
</span></p>
<p class="MsoNormal">3. An Occurrence may be typed using dcterms:type
(having
values such as dcmitype:PhysicalObject, dcmitype:Sound, or
dcmitype:StillImage)
and dwc:basisOfRecord (having values such as dwctype:PreservedSpecimen,
dwctype:LivingSpecimen, and dwctype:HumanObservation).<span style=""> </span>However,
the typing of an Occurrence again
does not imply fitness of use for any particular purpose.<span style="">
</span>An Occurrence of a particular type may be
used for any or all purposes for which it is useful.<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">B. HOW DO WE KNOW WHICH OCCURRENCES ARE USEFUL FOR
DOCUMENTING
DISTRIBUTIONS?</p>
<p class="MsoNormal">Having made the point that an Occurrence does not
have an
implied fitness for any particular use, it is true that one of the most
common
uses of DwC in the past has been to describe the metadata required to
document
the presence of organisms for the purpose of describing species'
distributions.<span style=""> </span><span style=""> </span>I
don't know if there is an official term for this use, but I'm going to
refer to
it as the "distribution documentation" use.<span style=""> </span>In
the current Darwin Core standard, this use
is facilitated by the term dwc:establishmentMeans
(<a class="moz-txt-link-freetext" href="http://rs.tdwg.org/dwc/terms/index.htm#establishmentMeans">http://rs.tdwg.org/dwc/terms/index.htm#establishmentMeans</a>),
which is defined as "the process by which the biological individual(s)
represented in the Occurrence became established at the location."<span
style=""> </span>dwc:establishmentMeans helps a metadata user
to assess the fitness of a record for distribution documentation by
differentiating between individual organisms that occur naturally and
those
that do not.<span style=""> </span>Because
dwc:establishmentMeans allows for values that span the range of native
to adventive/naturalized
to cultivated, a metadata user can select a level of stringency when
searching.<span style=""> </span>dwc:establishmentMeans assumes that
any type
of Occurrence can be used to document the individual.<span style=""> </span>However,
not all Occurrences are suitable for
distribution documentation.<span style=""> </span>So an
important question is: under what circumstances do Occurrences provide
useful
information for documenting a species distribution? <span style=""> </span>Another
important question which should be
addressed is: which Occurrence records should have
dwc:establishmentMeans as a
property? (or should dwc:establishmentMeans should be a property of
something
other than Occurrences?)<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">C. EXAMPLES</p>
<p class="MsoNormal">In discussing these questions, I will use some
examples
which range from a relatively simple circumstance (preserved specimens
in a
museum or herbarium collection) to more complex networks of various
kinds of
resources.</p>
<p class="MsoNormal">Example 1:
<a class="moz-txt-link-freetext" href="http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-herbarium.gif">http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-herbarium.gif</a></p>
<p class="MsoNormal">Example 2:
<a class="moz-txt-link-freetext" href="http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-insect.gif">http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-insect.gif</a></p>
<p class="MsoNormal">Example 3:
<a class="moz-txt-link-freetext" href="http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-botanical.gif">http://people.vanderbilt.edu/~steve.baskauf/conceptual-scheme-botanical.gif</a></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The starting point in all of these example
diagrams is an
Individual organism found in the environment.<span style="">
</span>By Individual I mean the object of the term dwc:individualID,
which is
the entity that a dwcterm:Occurrence documents and is described by the
class
proposed for DwC at:
<a class="moz-txt-link-freetext" href="http://code.google.com/p/darwincore/issues/detail?id=69">http://code.google.com/p/darwincore/issues/detail?id=69</a>.<span style="">
</span>(As a practical matter an
"Individual" may also represent a small population of organisms of
the same species.)<span style=""> </span>This Individual is
the entity that dwc:establishmentMeans describes.<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The Occurrence resources that are created are
represented by
the rectangles in the diagram.<span style=""> </span>In these
examples they are primarily specimens and images but they could also be
other
types of resources.<span style=""> </span>Each Occurrence is
associated with a particular dcmitype:Event in which the Occurrence
resource
was created (an "Occurrence resource creation event" described by the
date/time and dcterms:Location of the event and represented by arrows
in the
diagram). <span style=""> </span>Because of the one-to-one
relationship between an Occurrence resource and the Event in which it
is
created, I have chosen to think of the metadata for both things as a
single
unit.<span style=""> </span>One could also divide them
conceptually into two separate entities, i.e. different resources
having
different identifiers.<span style=""> </span>Whether this
approach is desirable or not should probably be the subject of a
separate
thread.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">D. WHICH OCCURRENCES CONTAIN LOCATION INFORMATION
ABOUT
INDIVIDUALS?</p>
<p class="MsoNormal">Since each Occurrence resource has location
metadata
associated with its resource creation event, each one has the potential
for
providing information to document a distribution. <span style=""> </span>However
it is clear from these diagrams that
the location metadata for many of these Occurrences has no use for
distribution
documentation because the Occurrences were created in locations that
have no
relationship to the Individual (e.g. the location in a lab where a DNA
sample
was extracted or in a museum where an image was created from a
specimen).<span style=""> </span>Examination of all three examples
shows that
the resource creation events for Occurrences that are derived directly
from the
Individual (highlighted in gray) provide useful information about where
the
Individual was at a particular time (i.e. distribution documentation),
while
the resource creation events for all of the other Occurrences do not.<span
style=""> </span>(Note that whether or not an Occurrence
documents the distribution of the Individual's species is not related
to the
type [dcterms:type or dwc:basisOfRecord] of the resource.)<span style="">
</span>It seems to me that there is a need for a
Darwin Core term that indicates whether the location metadata for a
particular
Occurrence resource creation event is useful for distribution
documentation - I
can't see any terms currently in the standard that can serve this
function.<span style=""> </span>Perhaps term could be created such
as "documentsDistribution" having values of "true" for
those derived directly from the Individual and "false" for those that
are not.<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">E. TO WHAT DOES dwc:establishmentMeans APPLY?<br>
</p>
<p class="MsoNormal">Currently dwc:establishmentMeans is assigned to
the class
Occurrence. <span style=""> </span>So theoretically, a value
for the dwc:establishmentMeans of the Individual could be assigned to
any
Occurrence resource/resource creation event derived from the Individual
regardless of how far the Occurrence is removed from the Individual
through
multiple resource creation events.<span style=""> </span>I
believe that this would probably be a bad idea, since the person
creating the
metadata for more distantly derived resources (i.e. a technician doing
a DNA
extraction or photographing a leg on a pinned specimen in example 2)
may not
have a clue about the status of the original Individual.<span style="">
</span>At best, that person would just copy the
value of dwc:establishmentMeans from the metadata for some other
Occurrence
resource derived more directly from the Individual, which would be
rather
pointless.<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Alternatively, dwc:establishmentMeans could be
assigned only
to Occurrence resources/resource creation events for which
"documentsDistribution"="true".<span style=""> </span>One could argue
that each collector/observer
(i.e. the object of dwc:recordedBy) of an Occurrence derived directly
from the
Individual could theoretically make an independent assessment of the
correct value
of dwc:establishmentMeans for the Individual.<span style="">
</span>It could also be argued that dwc:establishmentMeans should be
associated
with particular Occurrences because if an Individual's
dwc:establishmentMeans status
changed over time, then multiple Occurrences recorded from that
Individual over
time could have different values of dwc:establishmentMeans.<span
style=""> </span>However, it is difficult for me to imagine
circumstances under which this would happen.<span style="">
</span>An Individual that was "cultivated" is not likely to become
"native"
or vice-versa.<span style=""> </span>The one situation I can
imagine is if a "native" (or "adventive/naturalized") individual
were collected and moved to a zoo or botanical garden.<span style=""> </span>However,
in that circumstance, upon
collection the organism would cease to be in its natural environment
and would conceptually
become an Occurrence of type dwctype:LivingSpecimen rather than an
Individual.<span style=""> </span>In such a circumstance, the
value of dwc:establishmentMeans for the LivingSpecimen metadata should
be
"native" (or "adventive/naturalized") because establishmentMeans
refers to "the biological individual(s) represented in the Occurrence",
not to the Occurrence itself, and at the time of its collection, the
Individual's establishmentMeans was "native" (or
"adventive/naturalized").<span style=""> </span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">To me, the most logical thing would be to
re-assign
dwc:establishmentMeans from the class dwc:Occurrence to the proposed
Darwin
Core class Individual.<span style=""> </span>That makes sense
to me because after all, dwc:establishmentMeans is supposed to tell us
something about an Individual.<span style=""> </span>However,
there could be a couple problems with this.<span style="">
</span>One is that it is likely that many collectors of preserved
specimens
(e.g. who have simple resource creation circumstances such as in
example 1) are
not going to see any reason to bother with the concept of Individuals.<span
style=""> </span>If they do not create records for
Individuals, then in what context will they assign a value of
dwc:establishmentMeans?<span style=""> </span>The other
problem that I foresee is if two different collector/observers created
recorded
Occurrences from the same Individual but assigned the Individual
different
values of dwc:establishmentMeans.<span style=""> </span>When
those two Individual records are merged into one, there would either
have to be
some kind of rule for determining which value of dwc:establishmentMeans
to use,
or two values of dwc:establishmentMeans would have to be allowed for a
single Individual.<span style=""> </span>However, it seems to me that
this circumstance
would probably occur only very rarely.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">F. SUMMARY</p>
<p class="MsoNormal">It seems to me that two things are needed here to
meet the
needs of users who create complex networks of Occurrence resources such
as in
Examples 2 and 3.<span style=""> </span></p>
<p class="MsoNormal">1. A term such as "documentsDistribution" is
needed to unambiguously indicate whether the dcterms:Location and
dcmitype:Event (i.e. resource creation event) metadata for a particular
Occurrence provide useful information about the Individual that the
Occurrence
represents. <span style=""> </span></p>
<p class="MsoNormal">2. Clarification of whether the term
dwc:establishmentMeans
should be a part of the metadata for individual Occurrence resources
(and if
so, which ones) or whether it should be moved to the proposed class
Individual.</p>
<p class="MsoNormal"><o:p> Comments???</o:p></p>
<p class="MsoNormal">Steve Baskauf</p>
<pre class="moz-signature" cols="72">--
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
<a class="moz-txt-link-freetext" href="http://bioimages.vanderbilt.edu">http://bioimages.vanderbilt.edu</a>
</pre>
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