This 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:

1. Standards for date / time values? (3)

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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

Richard Pyle wrote:

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RE: CollectingDatesInterpreted When would this field *not* be set to true?

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Date: Mon, 27 Feb 2006 10:58:54 -0500 From: Michael Lee mikelee@EMAIL.UNC.EDU Subject: Re: Standards for date / time values?

Hello all,

It seems to me that the VerbatimDate/EarliestDate/LatestDate are helpful, but combine two separate issues:

1. duration of the event spanning more than one date/time unit
2. error associated with the date.

Is the distinction useful? Probably depends on your application of the date.

To handle these, VegBank uses three fields:

startDateTime stopDateTime dateTimeAccuracy (note that there is NO verbatimDate)

StartDateTime is most precise known date/time for the beginning of an event (in our case an observation of a vegetation plot) and the EndDateTime is the end date/time (which could have the same value). DateTimeAccuracy is a string with a list of values ranging from 1 second to 1 day to 1 year to 5,10 years, etc.

start and stop deal with issue #1 above, duration (potentially) exceeding usual date description precision.

The accuracy field deals with isue #2 above, error or uncertainty regarding the dates. It is this accuracy field that seems to be missing from this discussion thus far.

As far as time zones go, error on the order of hours isn't TOO important to us, so we don't worry about it too much. But I think what we're aiming to do is to store the date/time according to UTC. This means that to reconstruct what time the person saw something, the original time zone and Daylight Savings Time would need to be known, but this isn't crucial to us, either.

I like Lynn's list of weird dates, so I'll throw in what we'd do with them (this of course being "interpreted" but as Rich says, that's almost always the case):

PRE-1975 Start:null ; End: 01-JAN-1975 ; Accuracy: null or possibly a large value post-1992 Start: 01-Jan-1992; End:null ; Accuracy: null or possibly a large value summer 2001 Start: 15-JUL-2001; End:15-JUL-2001 ; Accuracy: 1.5 months Mid-1990s Start: 01-JUL-1995; End: 01-JUL-1995 ; Accuracy: 2 years late 1950's Start: 01-JAN-1958; End: 01-JAN-1958; Accuracy: 2.5 years Circa 1941 Start: 01-JUL-1941; End:01-JUL-1941; Accuracy: 6 months Early 1990s Start: 01-JAN-1992; End:01-JAN-1992; Accuracy: 2 years

Except for the "pre-Date" and "post-Date" I have assumed a relatively short duration. But this is interpreted. The problems with this approach I see are:

1. accuracy for start and stop dates could be different
2. accuracy is not a black and white idea. It's often more of a

gradient. Seems illogical to specify 10 years as accuracy in the first 2 examples, as the dates could be much more than 10 years away. 3) a closed list on accuracy seems to force you into decisions you don't

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