[tdwg-content] Treatise on Occurrence, tokens, and basisOfRecord

Steve Baskauf steve.baskauf at vanderbilt.edu
Sun Oct 24 01:02:56 CEST 2010

I have been dreading trying to write this post which I have promised (or 
threatened depending on if you have enjoyed or been annoyed by the 
previous lengthy thread) for some time.  I have dreaded it because this 
is a complicated subject and not one that is amenable to terse 
messages.  However, after the previous conversation with Rich et al., I 
feel for the first time that I have the questions (not answers!) clearly 
in my mind.  So rather than starting off rambling about LivingSpecimens 
and establishmentMeans as I had planned, I'm going to start by laying 
down several principles that have come into clarity in my mind after the 
previous conversation and the attempt to map things out in a diagram.  I 
will apologize in advance for failure to use the correct database or IT 
technical terms when I'm in unfamiliar territory. Until there is a 
consensus about how we deal with the "tokens" we use to document 
Occurrences, I'm not sure that what I have to say about those other 
topics will make sense.


PRINCIPLES (derived from earlier discussion)

1.  We have a number of kinds of "things" (which I will henceforth refer 
to as "resources") that are useful for describing and organizing 
metadata that we collect in our attempts to document biodiversity.  For 
many of these types of resources, we have defined classes to categorize 
the terms that can be used to describe the properties of resources that 
are instances of that class.  Describing the class helps us to 
understand the type of resources that constitute instances of that class.


2. A conscious decision was made to avoid formally defining rdfs:domain 
for Darwin Core terms.  This decision was made to provide flexibility in 
the way the terms can be used and to avoid the situation where semantic 
clients would draw incorrect or silly conclusions about what kind of 
things resources are.  However, this decision does not excuse us from 
thinking carefully about whether a term can be appropriately applied to 
a resource that is a member of some class (e.g. should we say that a 
digital photograph has a scientific name?).  Placing a term within a 
class is a suggestion that the term would appropriately be applied as a 
property of an instance of a class.


3. When users want to "flatten" and simplify their databases, they tend 
to eliminate one-to-many (1:M) relationships in favor of one-to-one 
(1:1) relationships.  The result of that is differences like we saw in

http://bioimages.vanderbilt.edu/pages/rich-diagram1.gif (which allows 
1:M relationships between Occurrences and Events and between Events and 
Locations) and

http://bioimages.vanderbilt.edu/pages/rich-diagram2.gif (which 
"atomizes" every Occurrence by considering it to have its own separate 
eventTime and Location information). 

A. There is nothing intrinsically "right" or "wrong" about either of 
these approaches, because they each have their own advantages.  The 1:M 
approach is more efficient, but results in a more complicated database, 
while the 1:1 approach results in a simpler database but may require 
repeating some or many term values in the records. 

B. The choices that users make in these situations is the cause of much 
of the disagreement about whether a certain class should exist or not 
since the people taking the 1:1 approach "collapse" the relationship 
diagram and eliminate classes they don't need while people who take the 
1:M approach need instances of the class to act as nodes to connect 
their "many" resources to some other thing. 

C. This collapsing of the diagram is also the reason for some 
disagreement about whether a term belongs in a certain class or not.  In 
the example above, 1:1 people would say that eventDate is a property of 
an Occurrence, while 1:M people would say that eventDate is a property 
of an Event.   

D. The choice of users on this issue influences their decision about 
whether or not to create resources that are instances of classes and 
hence to assign them identifiers.  If users take the 1:M approach, they 
need identifiers for resources that are acting as connecting nodes so 
that they can make reference to that resource in the metadata of the 
many things they are connecting to it.  If users take the 1:1 approach, 
they probably will skip creating explicit resources (and their 
corresponding identifiers) for resources of the class that they are 
"collapsing" out of the diagram). 


4.  I would propose that the "right" relationship diagram is not 
necessarily one that caters to a certain "right" philosophical point of 
view.  Rather, the "right" diagram is the one that allows users to 
define the relationships that they need for the organization of their 
metadata in the simplest manner, and which provides the most clarity 
about what resources of various kinds are, and how they are connected. 

A.  "Right" as I have defined it above depends on how broadly applicable 
the relationship diagram is intended to apply.  An individual person or 
organization with limited interests may have a relationship diagram that 
is simpler than the diagram shown at 
http://bioimages.vanderbilt.edu/pages/rich-diagram1.gif or might choose 
to add classes for other things that are their personal interest.  An 
organization interested focused on different issues or with broader 
interests might opt for many more or different classes that would be 
connected to those shown in the diagram. 

B. Given what I just said in A, what is "right" for Darwin Core is going 
to be defined by the needs of the Darwin Core constituency.  At the TDWG 
meeting, John Wieczorek made a statement which I will paraphrase as "in 
order for a term to make it into Darwin Core, at least two people had to 
want it".  I'm not sure to what extent he was joking about this, but it 
makes the point that one must consider community needs before saying 
that a certain part of the "diagram" is necessary.  I think that the 
reason that Rich and I were so quickly able to come to a consensus on 
the organization of the left side of the diagram is because he realized 
that there was a significant part of the DwC constituency that needed a 
way to group occurrences (i.e. needed Individuals) and I realized that 
there was a significant part of the constituency that needed to group 
multiple Events at a Locality and multiple Occurrences at an Event.  So 
in evaluating alternative conceptual systems for organizing resources, 
the question has to be asked as to the extent that an alternative allows 
broad segments of the DwC constituency to organize their metadata in an 
efficient and conceptually sensible way.  If one alternative is more 
broadly applicable and conceptually clear than another, then that 
alternative is better regardless of the philosophical underpinnings of 
the argument. 


5. The last point is one that has run as an undercurrent through various 
TDWG threads but which may not have been explicitly stated in this 
particular thread.  That is that there should be a separation between 
what a resource IS and what we want to use a resource FOR.  To use 
technical terms, we need to separate the "type" of a resource from its 
fitness of use.  A digital image IS a digital image.  It might be used 
FOR documenting that an organism was at a particular location at a 
particular time, but it could be used to illustrate a character, as a 
part of a visual key, as media for an educational presentation, as art, 
and probably many other things that aren't popping into my mind at the 
moment.  I believe that much of the confusion about "what is an 
Occurrence" comes from a failure to make this distinction.  



Earlier in the thread of "What is an Occurrence", there was a general 
consensus that an Occurrence often had a "thing" that was associated 
with it that served as evidence that a taxon representative (i.e. 
Individual) occurred at a particular Location at a particular time.  In 
my Biodiversity Informatics paper, I called this thing a 
"representation", but I now believe that "token" is a better term and 
will use it hereafter.  There also seemed to be a consensus that an 
observation was simply an Occurrence that did not have an associated 
token.  (This is with the understanding that observation is being 
narrowly defined as a type of Occurrence, with a definable time and 
location, as opposed to what I called the "checklist" definition which 
indicated that some undefined taxon representative was present in some 
defined geographical area at an indefinite time.)  In one of my earlier 
posts, I pleaded for somebody to tell me whether there was an assumption 
that the token was considered a part of the Occurrence or whether it was 
a separate thing.  I did not get any responses, which I'm construing to 
mean that people weren't sure about this.  At the present, I now have a 
clearer idea of the general principles I outlined above, and also have 
the "Rich" diagram for modeling relationships, so I'm going to again 
pose this question, but in what I hope is a clearer way.  I have re-made 
the earlier diagram as Rich suggested, using triangles rather than 
arrows.  The wide side of the triangle is the "many" side of the 
relationship and the point is the "one" side.  As before, I'm deferring 
on the right side of the diagram (to the right of Identification) to the 
taxonomists for now, so let's keep that out of the discussion for the 
moment.  I have also clarified the diagram by coloring in the actual DwC 
classes to distinguish them from selected terms that fall within those 
classes (non-colored boxes) and which can be used as properties of 
resources that are instances of the class.  The two alternatives that 
I'm discussion are:

http://bioimages.vanderbilt.edu/pages/token-assumed.gif which I will 
refer to as the "assumed token" model and

http://bioimages.vanderbilt.edu/pages/token-explicit.gif which I will 
refer to as the "explicit token" model. 


I believe that historically the assumed token model has been the one 
which most people have had in mind.  Before the new DwC standard, we had 
specimens and we had observations.  In order to avoid redundancies in 
terms for those two types of "things", a combined "thing" called 
"Occurrence" was created.  An Occurrence that was an observation didn't 
have a token and an Occurrence that was a specimen had a physical or 
living specimen as its token.  That's all pretty simple and sensible and 
we see evidence of this kind of thinking on the descriptions given 
http://rs.tdwg.org/dwc/terms/index.htm .  A record for an Occurrence has 
a thing called its dwc:basisOfRecord that presumably describes the kind 
of token (if any).  So if the token were a preserved specimen, we would 
say that [Occurrence] basisOfRecord [PreservedSpecimen].  If there were 
no token we would say [Occurrence] basisOfRecord [HumanObservation] or 
[Occurrence] basisOfRecord [MachineObservation].  Referring back to the 
assumed token diagram, in the case of a specimen there is no explicit 
reference to the specimen as a separate entity.  The terms related to 
the specimen, such as preparations and disposition are just plopped into 
the Occurrence class which implies that they are properties of the 
Occurrence itself. 


There seems to be a general consensus that other kinds of tokens can be 
used to document an Occurrence.  However, the way that the current 
Darwin Core terms are designed and placed within classes are very 
inconsistent as to how they handle types of tokens other than 
specimens.  According to the instructions at the top of 
http://rs.tdwg.org/dwc/terms/index.htm, a camera trap bird sighting 
should have [Occurrence] basisOfRecord [MachineObservation].  It is not 
clear how one is supposed to handle the actually metadata for the image 
that serves as the token.  Unlike specimens where the token's metadata 
terms are placed in the Occurrence class, I guess in the case of an 
image one is supposed to use associatedMedia to link the so-called 
MachineObservation to the image record.  If DNA were extracted, one 
would link the sequence to the Occurrence using associatedSequences 
(although it's not clear to me what the basisOfRecord for that would be 
- "TookATissueSample"?).  But what does one do for other kinds of 
tokens, like seeds or tissue samples - create terms like associatedSeed 
and associatedTissueSample?  I think that the ResourceRelationship terms 
were supposed to handle this problem, but I have yet to see an example 
of exactly how this was supposed to work. 


As an attempt to resolve this confusion in my mind, I wrote the 
Biodiversity Informatics paper that I've promoted frequently on this 
list (https://journals.ku.edu/index.php/jbi/article/view/3664).  In that 
paper, I take the basic assumed token model and broaden it in an attempt 
to make the assumed token model work for all kinds of tokens.  Because I 
assumed that each occurrence has a single token, I "collapsed the 
diagram" and connected the properties of the token directly to the 
Occurrence resource (as was modeled when specimen properties were placed 
within the Occurrence class).  If there were several tokens for a given 
Individual, I "flattened" the records by creating a separate Occurrence 
resource for each token.  The model was generalized further by allowing 
secondary Occurrence records where the token was not derived directly 
from the organism but rather derived from a primary Occurrence record.  
In complicated circumstances such as those found in a botanical garden 
where a seed or cutting might be collected from a tree with subsequent 
generation of a LivingSpecimen which might have a PreservedSpecimen 
collected from it and a DigitalStillImage taken of the preserved 
specimen.  You can see examples of the complex types of situations I 
tried to handle at

http://bioimages.vanderbilt.edu/pages/conceptual-scheme-insect.gif and


I created my own terms (like sernec:derivativeOccurrence and 
sernec:derivedFrom) to describe the connections among the individual and 
the various layers of Occurrences. 


Does this system work?  Yes, but there are a number of problems 
associated with it.  The first problem is related to Principle 4 above.  
In order for this system to work, there needs to be a consensus in the 
DwC community about several things.  One is that each Occurrence must 
have only one token.  If we are going to "type" Occurrences by their 
basisOfRecord (and the acceptable values for basisOfRecord are 
officially DwC types, see 
http://rs.tdwg.org/dwc/terms/type-vocabulary/index.htm), then an 
Occurrence can't have two values for basisOfRecord.  It is clear from 
the discussion we've had that people would like to consider a single 
Occurrence to be able to have multiple tokens as documentation.  The 
second problem is that there needs to be a consensus that a secondary 
Occurrence can exist at all (i.e. can you call the image of a specimen 
"an Occurrence"?).  It is clear to me from the discussion that when 
people are thinking about what an Occurrence means, they have in mind 
the documentation of the time and place of the Individual in its 
environment.  In a previous communication, John Wieczorek clarified that 
terms describing Occurrences like recordedBy and eventDate should only 
apply to primary occurrences and that it would not be appropriate to use 
them as properties of what I'm calling a secondary occurrence (such as 
the image of a specimen).  So I dealt with this by creating a 
distinction between Occurrences that document the distribution of a 
taxon (using the term sernec:documentsDistribution) and those that 
don't.  This is something like the old validDistributionFlag, but I 
defined documentsDistribution specifically as having a value of "true" 
only for Occurrences that were derived directly from the Individual 
(gray arrows in the two diagrams from the paper). 


But I think that the worst "crime" of the system I suggested is 
violation of Principle 5 above.  By asserting an unvarying 1:1 
relationship between the Occurrence and its token and by collapsing my 
relationship diagram to not explicitly include a resource that is the 
token itself, I am confusing the USE of an Occurrence (to demonstrate 
that a representative of a taxon was present at a particular Location at 
a particular time) which what the token IS (a dead organism in a jar or 
glued to paper, an electronic representation of photon patterns, a 
series of characters representing a nucleotide sequence).  So I'm 
charging myself with this "crime", pleading guilty, and accepting my 
sentence, which is to admit that the system I suggested in the 
Biodiversity Informatics paper is "wrong" based on the principles I 
outlined above.  What this amounts to is an acceptance of the 
"rightness" of the explicit token model (in the sense that I defined 
"right" in Principle 3 above). 


However, if I'm going to make this admission, I demand that the other 
guilty parties also confess, namely people who want to assert that 
Occurrences have properties that actually are properties of specimens.  
If we are going to have a system that actually works, we can't straddle 
the fence and say that the assumed token model is correct for specimens 
and that the explicit token model is correct for every other kind of 
token.  If we accept the explicit token model, then specimen will have 
to come off of it's throne and be a token like all of the other ways 
that we provide evidence that an Occurrence happened.  If we accept the 
explicit token model, then as a biodiversity informatics resource type 
"observation" will have to disappear into a puff of nothingness just 
like the "luminescent ether", "centrifugal force", and other kinds of 
things that we thought we needed to have to explain things but which 
turned out to be unnecessary when we figured out more basic 
explanations.  A human observation will simply be an Occurrence that 
doesn't have a token (which is what I've heard some people say all 
along).  If we allow the Occurrence/token relationship to be a 
one-to-many relationship rather than one-to-one, then HumanObservation 
is just the one-to-zero case of the more general one-to-many.  For those 
of you who like the idea of a "machine observation", that is just an 
Occurrence with a token that is whatever type of resource that the 
machine produces (electronic data file, image of the organism, image of 
a graph, or whatever). 



If we accept the explicit token model over the assumed token model, a 
number of problems get solved.  Just as was the case with Events, people 
who want to flatten things out by having only one token per Occurrence 
can do so.  For example, if I want to atomize things by defining my 
Occurrence to have taken place during an Event that lasted only the one 
second within which my camera shutter clicked, I can do that and have 
only a single token associated with that Occurrence.  On the other hand, 
if others want to define their Occurrence as taking place over the time 
over which they photographed, collected a leaf tissue sample, and then 
collected a branch of a tree for an herbarium specimen, then they can do 
that and associate all of those tokens (one or more images, the tissue 
sample, and the preserved specimen) with the single Occurrence. 


Another important benefit will come down the line when we actually try 
to develop RDF templates.  Right now it is not exactly clear (at least 
to me) how properties should be divided up among resources that are 
being described in the RDF.  Based on the assumed token model, I have 
been including the metadata for the token within the container element 
for the Occurrence.  This leads to some of the kind of odd assertions 
that people have been objecting to, such as

[Occurrence] dcterms:rights ["(c) 2002 Steven J. Baskauf"] or

[Occurrence] preparations ["skin"]. 

In the explicit token model, dividing metadata up appropriately among 
separate Occurrence and token resources makes more sense, e.g.

[Occurrence] recordedBy ["Joe Curator"]

[image] dcterms:rights ["(c) 2002 Steven J. Baskauf"]

[specimen] preparations ["skin"]


If we wanted to be really explicit about this, we probably should have a 
separate class for PhysicalSpecimens and separate the terms that 
describe specimens from those that describe Occurrences in general.  
There might be some difficulty in doing this because there are some 
terms that might be hard to decide about, like catalogNumber.  I don't 
really think the catalogNumber is a property of the Occurrence, because 
it makes more sense to me to say

[specimen] catalogNumber ["12345"] than

[Occurrence] catalogNumber ["12345"]

Realistically, I can't see this kind of separation ever happening, given 
the amount of trouble it's been just to get a few people to admit that 
Individuals exist.  It is just too hard to get motion to happen in the 
TDWG community.  As a practical matter, people who "compress" the system 
(which we admit happens and make concession to in Principle 3) by having 
record tables where a single row contains the metadata for both the 
Occurrence and the token (i.e. treat it as a 1:1 relationship) will 
simply have a column heading for catalogNumber and not care whether the 
catalogNumber applies to the Occurrence or the token.  It's the people 
who want to do the more complicated stuff like simultaneously keep track 
of multiple tokens per Occurrence (like several images, a sound 
recording, and a specimen), people who want to write RDF, or people who 
want to merge databases containing many types of tokens who will have to 
pay attention to this distinction.  Physical specimens would really be 
the only kind of class we would have to create because there already is 
a rich vocabulary for media items that is separate from DwC (i.e. the 
MRTG schema) and there are probably also vocabularies for stuff like 
tissue samples and DNA sequences (although I'm not familiar with them). 



Bob has warned us about the dangers of asserting that a term always 
applies to a certain type of resource by asserting that the term has an 
rdfs:domain .  However, we should not avoid attempting to assert that a 
resource is itself of a certain type.  Describing the "type" of a 
resource is an important part of letting potential users assess the 
possible fitness of use of that resource.  For example, you can collect 
DNA from a preserved specimen but not from an image.  You can include an 
image in a print journal article but not a sound recording.  You can 
create build a range map from Occurrences, but not from DNA samples.  In 
RDF, one of the basic properties that should be described about every 
resource is its rdfs:type .  In the generic Linked Data world, you can 
pretty much use anything that you want as an rdfs:type .  If you decide 
to use something obscure, then the danger is that nobody else will have 
any idea what kind of thing you are describing.  The Draft TDWG GUID 
Applicability Statement recommendation 11 says that "Objects in the 
biodiversity informatics domain that are identified by a GUID should be 
typed using the TDWG ontology or other well-known vocabularies in 
accordance with the TDWG common architecture."  So in our community, we 
can't just type resources any way we want.  But exactly how we SHOULD 
type things isn't clear.  There isn't any functioning TDWG ontology at 
the moment.  I have found it useful to use the DwC class as the 
rdfs:type in my attempts to write RDF.  That works pretty well for 
things that have DwC classes.  But if we follow the explicit token 
model, we need to have some consensus on what we will use as the 
rdfs:type for the tokens.   At this point it looks to me like it would 
make sense to have the convention that for tokens one uses either a 
dcterms:type or a Darwin Core type (i.e. one of the types listed at 
http://rs.tdwg.org/dwc/terms/type-vocabulary/index.htm, although as I 
already noted, there is no need for HumanObservation in the case of 
describing a token because human observations don't have tokens).  There 
isn't any sort of "collision" here of the sort that happened right after 
the adoption of the Darwin Core Standard when we tried to merge the 
Dublin and Darwin Core types (see 
http://www.keytonature.eu/wiki/MRTGv08_Type_term_inconsistent_with_DwC and

with many following responses for the gruesome details) since rdfs:type 
doesn't demand any particular type vocabulary.  I'm not entirely happy 
with this approach because for digital still images the logical type 
would be dctype:StillImage, which doesn't give any indication as to 
whether the image is film or digital, but I guess at this point in the 
21^st century most consuming applications will probably just assume 
digital anyway. 


So (assuming that Individuals become a DwC class) I guess I don't really 
see that there is any problem in using the current Darwin Core classes 
to indicate the rdfs:type of every kind of resource that we would be 
reasonably likely to assign GUIDs to EXCEPT for tokens.  Typing of 
tokens could be done using a combination of Darwin Core and Dublin Core 
types.  What I'm left scratching my head about is basisOfRecord.  When I 
subscribed to the assumed token model (i.e. when I wrote the 
Biodiversity Informatics paper), I thought I knew what basisOfRecord 
meant.  It meant the kind of token that backed up an Occurrence.  So 
when I wrote RDF for a specimen (as in 
http://bioimages.vanderbilt.edu/rdf/examples/lsu000/0428.rdf) I used the 
"hand grenade" approach to typing.  I lobbed every kind of "typing" that 
I knew of at the Occurrence record for a specimen:

[Occurrence] rdfs:type [dwc:Occurrence]

[Occurrence] dwc:basisOfRecord [dwctype:PreservedSpecimen]


[Occurrence] dcterms:type [dctype:PhysicalObject]


Under the explicit token model, I would just use

[Occurrence] rdfs:type [dwc:Occurrence]

for the Occurrence and

[specimen] rdfs:type [dwctype:PreservedSpecimen]

for the specimen itself.  If I also took an image at the same time and 
wanted to say that it was part of the same Occurrence as the specimen, I 
would use

[image] rdfs:type [dctype:StillImage]


Under the explicit token model, I really can't see any use for 
dwc:basisOfRecord .  Despite the resolution of the "train wreck" 
involving dcterms:type that we narrowly avoided after the adoption of 
Darwin Core, the definition still says "the specific nature of the data 
record - a subtype of the dcterms:type."  I think this is clearly wrong 
because I think we established that it was NOT a subtype of dcterms:type 
in that discussion that I referenced above.  So what is 
basisOfRecord???  What is "the data record" of which we are describing 
the nature?  If it's the Occurrence, then I think the consensus that I'm 
hearing in the discussion is that an Occurrence data record shouldn't 
have as its type any of the dwctype terms except for 
dwctype:Occurrence.  So what are all of the other terms like 
PreservedSpecimen for??? 


Under the explicit token model, what we really need is NOT 
basisOfRecord.  What we need is some term like "dwc:tokenID" if you like 
the Darwin Core IDREF style or if you prefer the style of the Linked 
Data community "dwc:hasToken".  In both cases, the object of the term 
would be an identifier for the token that's associated with a subject 
Occurrence.  This term could be applied from zero (for observations) to 
many times to an Occurrence.  People who want to flatten everything out 
will just ignore this term and cram all their metadata for the 
Occurrence, token, Event, and Location onto one line in their metadata 
table.  People who are going to use any kind of one-to-many 
relationships at all will have to figure out how to handle that anyway 
and won't be daunted by having more than one dwc:tokenID per 
Occurrence.  In the spirit of the complicated resource relationship 
diagrams from my paper, one could link primary tokens (like specimens) 
to secondary tokens (like specimen images) by using dwc:tokenID as 
well.  Any kind of token (primary, secondary, tertiary, ad infinatum) 
could be linked to the occurrence that it supports with dwc:occurrenceID.



OK, I've now gone on for eight pages of text explaining the rationale 
behind the question.  So I'll return to the basic question: is the 
consensus for modeling the relationship between an Occurrence and 
associated token(s) the assumed token model:


or the explicit token model:




If we accept the assumed token model with all of its warts, then for 
consistency's sake, we must create dwctype terms for each of the types 
of tokens that people would reasonably want to use as evidence for 
Occurrences (and my proposal for adding DigitalStillImage as a Darwin 
Core type stands).  We must also resign ourselves to assigning a 
separate occurrence to each token that users want to use to document the 
presence of a taxon at a time and place.  We also must accept having 
goofy-sounding statements like

[Occurrence] dcterms:rights ["(c) 2002 Steven J. Baskauf"]


If we accept the explicit token model, then we need to either dump 
basisOfRecord or come up with some rational explanation for what it 
actually means (and my proposal to add DigitalStillImage as a Darwin 
Core type becomes irrelevant).  We also need to create some kind of term 
like dwc:tokenID that will allow connections to be made between 
Occurrence records and their tokens.  For people who want to flatten out 
their Occurrence records and put the tokens together with the Occurrence 
(i.e. "compress the diagram" to get rid of the token resource), and who 
feel some need to indicate the type of the token that they are using, 
let them use any appropriate term from the Dublin Core or Darwin Core 
types as a value for rdfs:type.


Until we make one of these choices or the other and "fix" Darwin Core to 
work in a consistent way, we are just going to continue to misunderstand 
each other because each person will just "know an Occurrence when they 
see it". 


In the interest of space, I am going to defer on explaining my opinions 
about LivingSpecimen and establishmentMeans.  Those explanations are 
contingent on the conclusion that we reach on this issue.



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:
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Nashville, TN 37235

office: 2128 Stevenson Center
phone: (615) 343-4582,  fax: (615) 343-6707

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