[tdwg-tag] "Class" attribute in DwC [SEC=UNCLASSIFIED]
pmurray at anbg.gov.au
Tue Aug 18 07:36:05 CEST 2015
On 9/08/2015 3:21 am, Richard Pyle wrote:
> I would NOT regard "HumanObservaton" as a subclass of "Event". I believe
> that "Event" should be kept clean as fundamentally an intersection between a
> Location instance and a point in time.
In which case, you would need a separate class for a thing that happens
at a time, but which is not located (and perhaps, as the philosophers
say, does not have an extension).
And this in a way is a reply to Bob's original question - why aren't
these relationships explicit? The reason is that the second you try to
make them so, you almost immediately start running into philosophical
conundrums that people have been debating for thousands of years. The
old "How many angels can dance on the head of a pin?" problem is an
exercise in distinguishing between things that are located and things
that are extended.
Something as abstract and basic as "thing that happens at a place and a
time" should be borrowed from someone else's vocabulary. The first
problem there is that if you do that, then if that other vocabulary
defines inference rules, then anyone that uses your vocabulary must
respect those rules or their ontology becomes inconsistent.
Another problem is that other people's vocabularies are never really
quite exactly what you need.
And the underlying problem is that something as simple as "a point in
time" is actually a really hard question. What about things that have a
duration, that happen over a couple of weeks? Things that are cyclic?
Points in time that you are uncertain or vaguely defined? What about the
distinction between something that happens over a two week period, and
something that is instantaneous but that is known to have happened over
a certain two week period; or that is known to have happened at least
once over that period; or that almost certainly will happen at some
period in the future (eg, a scheduled observation)? The second you try
to nail this stuff down, it immediately starts sprouting hair. It's
intractable and perhaps not the kind of thing that biologists can best
spend their time doing.
Here at biodiversity.org.au, our new APNI dataset is exposed using a
custom made vocabulary (aside from things like dc:title) without much of
an attempt to describe our objects in terms of well-known classes. Maybe
at some point in the future we might be able to pull the TDWG, DwC, SKOS
terms into the data set. But that cant be done if those terms are so
strictly defined that our data in fact does not meet the strict
definitions of those terms. As it stands, our ontology does not connect
to other ontologies by way of the vocabulary in which it is described.
So is there any hope at all that we can create a distributed semantic
web of facts relating to taxonomy - the output of the taxonomic work
that people are doing)?
I think so, because the biologists and taxonomists are working on the
same stuff, certainly the same kinds of stuff, within the constraints of
the Real World™. And this maybe is a clue about where to look for useful
vocabulary. Rather than attempting to solve age-old questions about the
nature of time and thing, look to the specific subject matter.
After all - why have an 'event' class at all? The only thing you can do
with such a class is to construct a query that asks, for instance, "tell
me about everything whose foaf:person is Dr Joe Bloggs and that is a
thing that happened". On the other hand, "specimen" in the strict sense
of "something in a collection with an accession number" is very
important, fairly specific to the subject matter, and entirely worth
having a common term for.
Likewise, 'location' may mean 'geographic polygon', or it may
conceivably mean a collection, or an institution. (How so? Because a
location is anything that might be given in reply to the question 'where
is X?'. Notice that this is language-dependent). Each of these three
things has an existing vocabulary defined by geographers, librarians,
and (I suppose) company registrars respectively. Does anyone really need
a higer-layer linking them together?
Enough rambling, I think. FWIW:
* define the lower-layer objects and terms that people actually use when
they do taxonomy
* don't bother with the higher abstractions. That way lieth madness, and
is a time-sink.
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