Use Cases: 1) I am documenting an ISO-8601-compliant time variable from an instrument or application, which I would rather capture in its raw string form than convert to another form. 2) I would like to present some time variable in human-readable form, so that users of netCDF clients that have *not* found the holy grail of time conversions can quickly see whether records are from a time of interest, or are appropriately spaced, or have appropriate resolution, or.... (Note that among those users are people who look at binary dumps of files, of which I am one but I'm sure there are many others.)
Because of use case 1, I do not want to require that the time zone be declared. I think this practice should be encouraged as strongly as possible (even going so far as to include it as a strong recommendation in the definition). I dislike the 'local standard' approach that Roy mentions, because if I do not happen to be a SeaDataNet member who happens to have been around at that time and received that transmission of "best practices" (or have read it on the web somewhere), if there is a SeaDataNet file that I come across without time zones, I will naturally use the ISO *standard*. In that case, we've created anti-interoperability. John On Mar 19, 2013, at 12:08, Nan Galbraith <[email protected]> wrote: > There seems to be surprisingly broad support for this idea, so I've been > re-reading the thread, looking for a reasonable use case. I can't say that > I've found any description of why we actually need this - am I missing > something? > > Anyway, going back to Aleksandar's original (slightly amended) proposal of > Jan 11 just for a moment... I'd like to clarify one detail. As far as I > know, > ISO 8601 calls for the default time zone to be local, not UTC. > > If we're going to add this option to CF, we should *at least* require the > time > zone to be specified. Allowing a default, and having that default NOT align > with ISO, is just too much to ask. Either we're implementing ISO, or not - > changing the default meaning of the time zone would truly mislead our > imaginary post-apocalyptic researchers - and I know how much we all > worry about them. > > From Wikipedia (my only available ISO documentation): > > Time zones in ISO 8601 are represented as local time (with the location > unspecified), as UTC, or as an offset from UTC. > If no UTC relation information is given with a time representation, the > time is assumed to be in local time. > > Cheers - Nan > > > On 1/11/13 12:00 PM, Aleksandar Jelenak - NOAA Affiliate wrote: >> Dear All: >> >> Here's the modified proposal for the datetime_iso8601 standard name: >> >> standard_name: datetime_iso8601 >> >> Units: N/A >> >> String representing date-time information according to the ISO >> 8601:2004(E) standard. Variables with this standard name cannot serve >> as coordinate variables. Date-time information is in the Gregorian >> calendar. For dates preceding the Gregorian calendar the date-time >> information is in the proleptic Gregorian calendar. Possible date-time >> string forms are: >> >> <datetime> = <date> "T" <time> <timezone> ; >> >> <date> = YYYY "-" MM "-" DD | YYYY "-" DDD ; >> >> <time> = hh | hh ":" mm | hh ":" mm ":" ss | hh ":" mm ":" ss "." S >> | hh ":" mm ":" ss "," S ; >> >> <timezone> = "" | "Z" | "+" hh | "+" hh ":" mm | "-" hh | "-" hh ":" mm >> >> Where: >> >> * "YYYY" is a four-digit year (0000-9999). >> * "MM" is a two-digit month of the year (01-12). >> * "DD" is a two-digit day of the month (01-31). >> * "DDD" is a three-digit ordinal day of the year (001-366). >> * "hh" is a two-digit hour (00-23). >> * "mm" is a two-digit minute (00-59) >> * "ss" is a two-digit second (00-60). >> * "S" is one or more digits representing a decimal fraction of the >> second. >> >> * The value of any designator when not specified is zero. >> >> * If <timezone> is ommitted the default value is "Z". >> > > > -- > ******************************************************* > * Nan Galbraith Information Systems Specialist * > * Upper Ocean Processes Group Mail Stop 29 * > * Woods Hole Oceanographic Institution * > * Woods Hole, MA 02543 (508) 289-2444 * > ******************************************************* > > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ---------------- John Graybeal <mailto:[email protected]> phone: 858-534-2162 Product Manager Ocean Observatories Initiative Cyberinfrastructure Project: http://ci.oceanobservatories.org Marine Metadata Interoperability Project: http://marinemetadata.org
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