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 <ngalbraith at whoi.edu> 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 *
> *******************************************************
>
>
> _______________________________________________
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> CF-metadata at cgd.ucar.edu
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----------------
John Graybeal <mailto:jgraybeal at ucsd.edu> 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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