[tdwg-content] Heretics and illuminati, oh my! [SEC=UNCLASSIFIED]
Steve Baskauf
steve.baskauf at vanderbilt.edu
Mon May 9 22:53:58 CEST 2011
Being either fearless or a fool (is there actually a difference?), I
shall tread into this subject area at which I am a mere novice. So be
kind...
I think that there may be several "solutions" to this problem. The one
that is "correct" probably depends on what one is trying to accomplish.
So I will try to describe in the most succinct way what Cam and I were
trying to accomplish with DSW, and how that fits in with this thread.
Cam and I basically wanted to do two things:
1. Make it possible to use GUIDs RIGHT NOW (not five years from now).
2. Create an extremely stripped down ontology that would be
non-controversial enough that people might actually use it, but which
wouldn't do anything so bad that it would inhibit future development in
the Semantic Web context (i.e. it could be extended in the future by
clever people to do clever Semantic Web stuff).
Amazingly, the GUID Applicability Statement has achieved the status of
Standard-hood! (http://www.tdwg.org/standards/150/) Hooray! I sort of
missed the announcement, but ran across the fact the other day when I
was surfing through the TDWG website. Since the GUID A.S. is now a TDWG
Standard, I would say it would now officially be a best-practice to
follow it. In particular, Recommendation 11 states "Objects in the
biodiversity 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." This is somewhat problematic, given that
the TDWG ontology (with the possible exception of the Taxon/TaxonConcept
part) is effectively ("socially"?) deprecated. What is the alternative
"other well-known vocabulary"? There is none, at least none having any
kind of official status with TDWG.
I recently discovered (or maybe re-discovered) the Technical
Architecture Group (TAG) Technical Roadmaps from 2006-2008:
http://www.tdwg.org/uploads/media/TAG_Roadmap_01.doc
http://www.tdwg.org/fileadmin/subgroups/tag/TAG_Roadmap_2007_final.pdf
http://www.tdwg.org/fileadmin/subgroups/tag/TAG_Roadmap_2008.pdf
I might have seen them before, but if so it was at the point where I was
really not knowledgeable enough to comprehend them. I found it very
instructive to read about what the TAG had in mind when it set out to
create the TDWG Ontology. In particular (from the 2007 Roadmap):
"From the point of view of exchanging data - such as in the federation
of a number of natural history collections - there is no need for a
standards architecture. The federation is a closed system where a
single exchange format can be agreed on. ... This model has worked well
in the past but it does not meet the primary use case that is emerging.
Biodiversity research is typically carried out by combining data of
different kinds from multiple sources. The providers of data do not know
who will use their data or how it will be combined with data from other
sources. The consumer needs some level of commonality across all the
data received so that it can be combined for analysis without the need
to write computer software for every new combination." [This brings to
mind the very "different kinds" of resources Cam is documenting in
Borneo and the "multiple sources" that will be handling the metadata
once those resources are sent off to herbaria, labs, and arboreta.]
and from the 2008 Roadmap:
"If GUIDs are used to uniquely identify 'pieces' of data we need to have
a shared understanding of what we mean by a 'piece of data' i.e. what
kind of thing is it that a particular id applies to, a specimen, a
person, an observation, a complete data set. We also need to have a
shared understanding of at least some of the properties we use to
describe these things."
Having been barely aware of TDWG's existence in 2008, I am blissfully
ignorant of whatever disagreements may have occurred regarding LSIDs,
reification, or whatever, and really don't want to know about them. All
I can say as an outside observer is that it appears that the failure of
the initial efforts to get GUIDs and the TDWG Ontology off the ground
was because the system envisioned was too complicated to maintain, too
complicated to gain a consensus, and to complicated to actually explain
to anybody. Now that GUIDs seem to have a new lease on life, it seems
like the greatest chance of successfully implementing them is to start
by keeping things absolutely as simple as possible. To Cam and me,
Darwin Core seemed to be the only candidate for something relatively
simple and relatively universally accepted on which one could base an
ontology that could be used to type GUIDs and to use to express "a
shared understanding of at least some of the properties used to
describe" biodiversity resources. Although I was somewhat skeptical
that there was a "community consensus" about what the DwC classes meant
and how they were related to each other, the exhaustive discussion on
this list in Oct/Nov convinced me that maybe there WAS a consensus, or
at least enough of a consensus to move forward. Although some people
may at the present time be interested in figuring out how to do things
like "define 'Fish' as an owl class as well as as a Taxon object", I
would assert that is outside the core mission of TDWG as stated: to
"develop, adopt and promote standards and guidelines for the recording
and exchange of data about organisms evidenced by the historical
record". It is fun to talk about, but to me not the primary
consideration in designing a community data exchange model. This
outlook explains to some extent why I asked questions about the
complexity of taxonconcept.org and its orientation toward facilitating
semantic queries. There is nothing wrong with that, but it doesn't seem
to be the direction that TDWG has said it wants to go. Perhaps when we
have "gotten there" (i.e. have a functioning system using GUIDs for
clearly typed resources), we might want to embark further down the road
to the Semantic Web.
Aside from just importing the DwC classes into the DSW ontology and
connecting them with object properties, Cam and I did a little nasty
thing with them. It has been said that declaring ranges and domains for
terms doesn't prevent people from using the terms to express
relationships among the "wrong" types of things. Rather, it simply
asserts that those things are instances of the classes used in the range
and domain declarations for the term. That is sort of true, but by
declaring many of the core DwC classes to be disjoint, we actually ARE
preventing people from using the wrong object properties with instances
of the wrong classes. If Joe Curator rdf:type's a determination as a
dwc:Identification, but then uses dsw:atEvent (which has the domain
dwc:Occurrence) as a property of the determination, then a reasoner will
infer that the determination is a type dwc:Occurrence as well as the
explicitly declared type dwc:Identification. Because dwc:Identification
and dwc:Occurrence are disjoint classes, the reasoner will have a fit.
Cam and I are being Naughty (sensu Bob Morris) because we are inhibiting
the extensibility of dsw:atEvent, but Joe Curator is being Naughty
(sensu Baskauf and Webb) because Cam and I believe in the statement from
the 2007 Roadmap: "The consumer needs some level of commonality across
all the data received...". Joe Curator is not being consistent with the
"shared understanding of at least some of the properties" to the extent
that DSW reflects the "shared understanding" of the TDWG community. We
are basically trying to enforce a sort of orthodoxy on the use of DwC
classes as rdf:types and on the connections between the dwc:classes so
that people can have some reasonable expectation that they are talking
the same language as their partners whose data are also being aggregated
in the same federated database.
It seems to me that this "enforcement of orthodoxy" may be very much at
odds with the free-wheeling spirit of the Semantic Web community where
Anybody Can Say Anything About Anything. But when I look over those old
TAG roadmaps, I see little having to do with clever Semantic
inferencing. I see a lot about providers and consumers understanding
what each other are talking about. To some extent, Darwin Core can
provide most of the necessary commonality between providers and
consumers. There were (in our opinion) three areas where it could not.
One was the lack of a class to link repeated sampling events and
determinations (dwc:IndividualOrganism or TaxonomicallyHomogeneousEntity
if you prefer) and another was a class that allowed for the separation
of evidence from the Occurrence documented by it (called by us the
dsw:Token class). The other area was the dwc:Taxon class which did not
seem clear enough in its definition nor to possess enough complexity to
express the kinds of relationships commonly discussed on this list.
dwc:Taxon needs to be "fixed" before it is Ready For Prime Time (i.e.
usable in rdf:type declarations)
So I guess having read the various responses to my query and thinking
about the history of the TDWG Ontology, I would say that it may not
really be important how dwc:Taxon could be tied to tc:Taxon because the
two classes probably don't need to be tied together anyway. As it
currently stands, dwc:Taxon (outside of DSW) has no semantic meaning
other than what people want to believe that it means because it's not
tied to any other classes by object properties of its instances. The
mish-mash of terms describing names and taxa listed under dwc:Taxon add
to the confusion - since the DwC vocabulary purposefully does not
declare domains for the terms listed under a class they really could be
used as properties for an instance of any class anywhere. In contract,
tc:Taxon does have properties that are described clearly in the TDWG
Ontology. The only reason that we declared the two classes to be
equivalent was to signal that we felt that some of the DwC terms listed
under dwc:Taxon in the DwC vocabulary could be used as data properties
for the things in the tc:Taxon class that people like Paul were
describing with properties from the TDWG Ontology. Tying them together
doesn't (at the moment) mess up anything that anybody is doing with
dwc:Taxon because (outside of DSW) there isn't anything to actually DO
with dwc:Taxon in RDF. However, the point is well taken that if someone
in the future did decide to define properties specifically intended for
use with dwc:Taxon, those properties would be hopelessly tangled with
tc:Taxon properties.
It seems to me like the real road forward (if one believes as I do that
DwC is the only practical alternative to use for typing GUIDs) would be to:
1. decide that the TDWG Ontology in its dead form adequately describes
taxa, names, and their properties (use it as-is). OR
2. decide that although the TDWG Ontology doesn't do everything that
people want it to do at the present time, it could resurrected and
modified to do what people want (use it and hope for the future). OR
3. decide to just create the additional classes, e.g. dwc:Name (or
dsw:Name if you prefer not to adulterate the "pure" Darwin Core), and
object properties for dwc:Taxon and dwc:Name that are needed to get the
job done (i.e. just dump the TDWG Ontology as unfixable and make up new
stuff).
In any of these three alternatives, there isn't actually any reason to
tie the two classes together that I can see. Of these three, I think
the third option would probably be preferable, although it might put
Paul (and any others currently using the TDWG Ontology to describe Taxon
instances) in the unpleasant position of having to redo their RDF.
Steve
Paul Murray wrote:
> On 09/05/2011, at 2:07 PM, Kevin Richards wrote:
>
>
>> Paul
>>
>> I had the same thought (ie the x is of type dwc:Taxon, y is of type tc:Taxon, we know dwc:Taxon and tc:Taxon are equivalent, so we can reasonably compare x and y).
>> And this is built into standard semantic web reasoners - which is a bonus.
>> But this was debated (taking into account Bob Morris' issue) with respect to DwC and it was decided the benefits weren't significantly better than having a "dwc:isInCategory" sort of property that could then be "equivalent to" another class property and therefore giving you a similar advantage (admittedly not as good, but similar).
>> Do you think this is reasonable or are we just losing too much semantic web benefits by not specifying the domain constraint?
>>
>
> A thing to watch out for is that in OWL DL, you cannot apply ordinary data and object properties to vocabulary objects (classes, predicates) - you can only apply annotation properties. If you apply an ordinary data property to a class, OWL DL treats this as what it calls "punning": it decides that there is a class named X and also a named individual named X, and that these have nothing to do with one another. The individual has properties, the class has members, and the annotation properties, well: whatever. Reasoners do not reason over annotation properties: indeed - that's the entire point. Attempting to put properties on properties and having classes being instances of classes results in things that are mathematically undecidable ("this statement cannot be proven to be true").
>
> (another reason is that is allows you to put dc:comments and labels on classes, and even if you declare those classes to be equivalent nevertheless the comment only applies to the particular thing you put it on)
>
> This all means that dwc:isInCategory, if you want to apply it to dwc:taxon or other classes, will never have any meaning that semweb "engines" can get at. The underlying thing is that dwc:isInCategory is actually a meta-syntactic construct: rather than using owl to define a vocabulary, you are effectively attempting to extend OWL itself.
>
> But ... maybe that's ok. Maybe what is attempting to be done here only ever needs to be understood by humans.
>
> Now ... if what you are trying to do is to define "Fish" as an owl class as well as as a Taxon object - that is do-able, even to the point of being able to get inheritance working, using reflexive properties. At least ... I think it is. I should write a test case.
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--
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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phone: (615) 343-4582, fax: (615) 343-6707
http://bioimages.vanderbilt.edu
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