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

Blum, Stan SBlum at calacademy.org
Wed Oct 27 09:31:59 CEST 2010


I think Rich's statements are consistent:

1) An Occurrence is the intersection of an Individual and an Event (has
place and time dimensions); and
2) an Occurrence is an Individual bounded by (in) space and time.

It would be incorrect to truncate #2 as: "an occurrence is an individual",
or even to say that an individual is_a (kind of) occurrence.

In general, however, I agree with your point, we should try to be precise in
our definitions.  This whole discussion about individuals and occurrences
has driven home one of my pet peeves.  A lot of people refer to the millions
of records made accessible by GBIF as species occurrence records.  I think
that's an unfortunate simplification; they are organism occurrence records.
People identify those organisms as being members of a species.  There is
metadata in those identifications, which enables the assessment of fitness
for use.


On 10/26/10 7:46 PM, "Hilmar Lapp" <hlapp at nescent.org> wrote:

> On Oct 25, 2010, at 4:37 AM, Cam Webb wrote:
>> But then what exactly are the Occurrences themselves?  From Richard
>> Pyle:
>>   ``So, an Occurrence is the intersection of an Individual and an
>> Event.
>>   An Event is a Location+Time[+other metadata].  Each Event may have
>>   multiple Occurrences (i.e., one for each distinct Individual at
>> the same
>>   Location+Time).  Also, an Individual may have multiple Occurrences
>> (one
>>   for each Event at which the same Individual was documented).''
>> So the Occurrence is the Individual _itself_ bounded by space and
>> time,
> While for the purposes of exchanging occurrence data in a commonly
> agreed upon markup, i.e., Darwin Core, this may be perfectly
> acceptable, I think there are some serious issues in the above when we
> try to tighten up the semantics so that machines could do something
> with them, or so they can seamlessly integrate into the semantic web.
> First there is an internal inconsistency: on the one hand occurrences
> *are* individuals (albeit only a subset - though see below), and on
> the other hand individuals *have* occurrences.
> Second, occurrence is said to be the intersection of an individual and
> an event, or an individual and space and time. In the semantic web,
> OWL models deal with sets of individuals. I would argue that the
> intersection set of an individual organism (or a set of individual
> organisms) and an event (or a set of events) is empty, because there
> are no events that are also individual organisms, and vice versa.
> Alternatively, and using "Individuals" as short hand for "instances of
> an organism" we could say that an Occurrence is the intersection of
> all Individuals belonging to a specific taxon, all Individuals at a
> specific location, and all Individuals existing at a specific time.
> Then an instance of an Occurrence would be an Individual in that
> intersection, and taxon, location, and time would be (among) its
> properties.
> Just some thoughts.
> -hilmar

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