[tdwg-content] Time ontology [SEC=UNCLASSIFIED]

Paul Murray pmurray at anbg.gov.au
Wed Oct 27 06:39:19 CEST 2010

> - Event occurred at a singular (imprecisely known) point between startDate
> and endDate
> - Event occurred at multiple points between startDate and endDate
> - Event occurred continuously beginning startDate and ending endDate

Has anyone seen http://www.w3.org/TR/owl-time/ ? There's a page of links here http://www.isi.edu/~hobbs/owl-time.html . Perhaps the way to go is contributing to that w3c draft - it seems very incomplete at present.

CalDAV has a model of time, but looking at it I don't think the concepts there will suit, and of course there is no OWL vocabulary.

I have had the dubious pleasure of modelling times and durations in java/sql on a couple of occasions. The main thing I concluded was that it is important to distinguish between a date range expressed in calendar units and the concept of a time interval in the sense of from and to an instant. To clearly distinguish discrete time from continuous time. In particular, it is very useful to treat timestamp intervals as being from some named instant up to *but not including* some other named instant. This is because our names for times always have a degree of granularity, depending on the naming scheme, and we take them to refer to the instant at the start of their range.

Doing this makes it easy to calculate total durations, to determine if two ranges are contiguous, disjoint, or overlapping, and to take intersections and unions. For instance, is the date range "2010-01-31T22:00 to 2010-01-31T23:59" contiguous with the date range "year 2011"? What interval of time covers all of May 1988 and all of Year 1920? You can easily answer if you convert them to their equivalent timestamp ranges ("up to but not including") according to the way each model divides up time into named bits. Attempting to do it any other way is very horrible. 

This means that "from 2011 to 2012" may have a duration of one year or two, depending on how you meant it, and there are types permitting you to be explicit.

It does seem that there ought to be a vocabulary for this sort of thing outside of rs.tdwg.org, which DwC can reference.

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