Hilmar,
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.
-Stan
On 10/26/10 7:46 PM, "Hilmar Lapp" hlapp@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