[Bug 7678] New: time zones and leap seconds

http://www.w3.org/Bugs/Public/show_bug.cgi?id=7678

           Summary: time zones and leap seconds
           Product: XML Schema
           Version: 1.1 only
          Platform: All
               URL: http://www.w3.org/TR/2009/CR-xmlschema11-2-20090430/#d-
                    t-values
        OS/Version: All
            Status: NEW
          Severity: minor
          Priority: P2
         Component: Datatypes: XSD Part 2
        AssignedTo: David_E3@VERIFONE.com
        ReportedBy: sla@ucolick.org
         QAContact: www-xml-schema-comments@w3.org
                CC: cmsmcq@blackmesatech.com


The date/time values specify that leap seconds are not to be handled.  There
are a few minor points to note.

The definition of leap second in the document says leap seconds can only occur
on some months, whereas ITU-R TF.460 allows for them at the end of any month.

For almost a decade the ITU-R has been discussing abandoning leap seconds.  The
process is closed and involves international diplomatic consensus.  There is no
way to predict the outcome.  Nevertheless, any outcome has implications for the
date/time values.

If the status quo persists, then leap seconds will continue and the document
already specifies their handling.

If leap seconds are abandoned altogether, then in about 600 years most nations
will probably choose to shift their timezone offsets from UTC, and that will
likely drive some zone offsets beyond the 840 minute limit which the schema
draft currently specifies.  This is clearly not an urgent issue, but one which
does affect posterity.

If the ITU-R decides to keep leap seconds in UTC, but remove them from the
broadcast time scale by changing its name, then many of the definitions of
terms will change.  The likely result is that POSIX time_t will become leap
free while UTC becomes just another timezone offset.  In that case the timezone
offsets will increment by one second for each leap second in UTC.  This sort of
change could come into effect within 10 years.  Whereas POSIX allows zone
offsets of seconds, the current XML schema with its specification of minutes
could be problematic.  This depends on whether the date/time is intended to
give the offset from whatever is called UTC, or from POSIX time_t.  If the
latter, then the schema would want to allow zone offsets measured in seconds.


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Received on Friday, 18 September 2009 23:34:51 UTC