Edward C. Zimmermann wrote: > http://xml.coverpages.org/ISO-FDIS-8601.pdf > > We have time intervals (5.5) and Recurring time-intervals (5.6) Thanks. At "4.1 Basic concepts" the specification says "three concepts are fundamental:" to list four concepts afterwards. :-) I'll skipp recurring time-intervals for simplicity. So there is (citing the specification): 1. Time-point: instant in the laps of time regarded as dimensionless Examples of simple time-points are dates. 2. Time-interval: a portion of time between two time-points. A time-interval is one of - a start and an end - a duration not associated with any start or end - a start and a duration - a duration and an end As I read the specification, a "start" or "end" is an instance of a time-point. Time intervals and Time points can be compared by the method "inside of". We now extend this model by introducing: 3. Time-collection: a set of time-points and/or time-intervals. 4. Time-choice: One of - a time-collection, that one unknown element is selected from - a time-interval, that one unknown time-interval or time-point is selected from 5. Approximate times: A time-point, time-interval, or time-collection marked as approximate. 6. Questionable times: A time-point, time-interval, time-collection, or approximate time marked as approximate. Jakob -- Jakob Vo� <[log in to unmask]>, skype: nichtich Verbundzentrale des GBV (VZG) / Common Library Network Platz der Goettinger Sieben 1, 37073 G�ttingen, Germany +49 (0)551 39-10242, http://www.gbv.de