Philip and John have convinced me that it is better to use the start/end date/time approach rather than the mid-point and uncertainty approach. Philip's arguments are very convincing.
Cheers
Arthur
From Philip.Gleeson@environment.nsw.gov.au on 27 Feb 2006:
I think the important point to remember in all of this is that time is linear and this allows for a simplified approach that is more difficult to apply in a 2-dimensional spatial situation. Where the boundaries of a
time interval are known the two approaches are identical and require two
data points to accurately specify the range. However, what of the situation where only one data point is known? It often occurs that one knows that a collection took place prior to a given date, or equally one
may know that a collection occurred after a given date with no other information. This is easily catered for when a start and end datetime are used, but if a middle point and an accuracy have to be specified on an unbounded time interval, how do you do this? In contrast, I am not aware
of any cases in collections where one has an accurate midpoint but is unsure of how far either side of this date the collection occurred. For this reason alone I would tend to lean towards the use of start and end dates over the alternative approach of a mid point and an accuracy as the latter can always be calculated from the former.
Philip Gleeson
Wildlife Data Officer Policy & Science Division Department of Environment & Conservation 43 Bridge St, Hurstville NSW 2220 Ph: 9585 6694
list.tdwg@ACHAPMAN.ORG Sent by: Taxonomic Databases Working Group List TDWG@LISTSERV.NHM.KU.EDU 28/02/06 18:12 Please respond to list.tdwg
To: TDWG@LISTSERV.NHM.KU.EDU cc: Subject: Dates and TimesThis is an interesting discussion, and I am wondering why we treat dates/times differently to localities where we may have "between two places", "near a place", "along a path", etc.
At this stage, we tend to recommend using a single location (lat/long) with an uncertainty surrounding that location. With location, we are currently using a circle to determine the uncertainty in a locality, where as time is linear (and thus easier). We may change to the use of polygons and uncertainty footprints at a later stage but let's leave that discussion for another time.
Would not the better way to handle some of these data/time situations be
to use a midpoint with an uncertainty. Thus for "01-2000" we should not
interpret that as 01-01-2000 but as 15-01-2000 with an uncertainty of 15
(or 16) days - can be refined with the incorporation of time. This is, of course, not all that dis-similar to what michael is suggesting.
On a related issue - if we have two dates - the dates may be "accurately" determined - but the actual time of occurrence is uncertain. I thus prefer the use of the term uncertainty - and possibly better (as we will
most likely use in the Georeferencing Best Practices document under preparation) - "Maximum Uncertainty" or perhaps "Maximum uncertainty estimate"
Perhaps there are good reasons for using start and end dates/times - if so I am happy to go along with that - but believe we should aim for consistency of approach if possible.
Cheers
Arthur
Arthur D. Chapman Australian Biodiversity Information Services Toowoomba, Australia
From Automatic digest processor LISTSERV@LISTSERV.NHM.KU.EDU on 27 Feb
2006:
There are 3 messages totalling 562 lines in this issue.
Topics of the day:
- Standards for date / time values? (3)
Date: Mon, 27 Feb 2006 12:27:23 +0100 From: Hannu Saarenmaa hsaarenmaa@GBIF.ORG Subject: Re: Standards for date / time values?
In my understanding the "Not interpreted" case would be just a text string "DateTimeSourceText", repeating whatever is written in the
label
about the dates and times. This can be useful if questions arise of
the
interpretation.
Btw., isn't he name of the element "EarliestDateCollected" in Darwin Core v.1.4 proposal a bit misleading as it really is "EarliestDateTimeCollected"?
Hannu
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