Profile of ISO 8601 (draft)

[Misha Wolf]

Introduction
============

This note defines a profile of [ISO 8601], the International Standard
for the representation of dates and times.  A discussion of [ISO 8601]
is available at [KUHN].  [ISO 8601] describes a large number of
date/time formats.  To reduce the scope for error and the complexity of
software, it is useful to restrict the supported formats to a small
number.  This profile defines a few date/time formats, likely to satisfy
most requirements.

The profile may be adopted by standards which require an unambiguous
representation of dates and times.  As different standards have their
own requirements regarding granularity and flexibility, this profile
offers a number of options.  An adopting standard must specify which of
these options it permits.


Summary
=======

This profile of [ISO 8601] defines four levels of granularity:

1.  Date only
2.  Date plus hours and minutes
3.  Date plus hours, minutes and seconds
4.  Date plus hours, minutes, seconds and decimal fractions of a second

An adopting standard must permit one or more of these options.

This profile defines two ways of handling time zone offsets:

1.  Times are expressed in UTC, with a special UTC designator ("Z").
2.  Times are expressed in local time, together with a time zone offset 
    in hours and minutes.  A time zone offset of "+hh:mm" indicates that
    the date/time uses a local time zone which is "hh" hours and "mm" 
    minutes ahead of UTC.  A time zone offset of "-hh:mm" indicates that
    the date/time uses a local time zone which is "hh" hours and "mm" 
    minutes behind UTC.

An adopting standard must permit one or both of these options, unless
the standard does not permit granularity options 2, 3 and 4.

This profile does not specify how many digits may be used to represent
the decimal fraction of a second.  An adopting standard must specify
both the minimum number of digits (a number greater than or equal to
one) and the maximum number of digits (the maximum may be stated to be
"unlimited"), unless the standard does not permit granularity option 4.


The formats
===========

1.  Date only
-------------

The format is: YYYY-MM-DD

Example:       1994-11-05

This example corresponds to November 5, 1994.


2.  Date plus hours and minutes
-------------------------------

If times are expressed in UTC, the format is:

               YYYY-MM-DDThh:mmZ

Example:       1994-11-05T13:15Z

If times are expressed in local time, together with a time zone offset,
the format is:

               YYYY-MM-DDThh:mm+hh:mm
or:
               YYYY-MM-DDThh:mm-hh:mm

Example:       1994-11-05T08:15-05:00

Both the examples in this section correspond to November 5, 1994, 8:15
am, US Eastern Standard Time.


3.  Date plus hours, minutes and seconds
----------------------------------------

If times are expressed in UTC, the format is:

               YYYY-MM-DDThh:mm:ssZ

Example:       1994-11-05T13:15:30Z

If times are expressed in local time, together with a time zone offset,
the format is:

               YYYY-MM-DDThh:mm:ss+hh:mm
or:
               YYYY-MM-DDThh:mm:ss-hh:mm

Example:       1994-11-05T08:15:30-05:00

Both the examples in this section correspond to November 5, 1994,
8:15:30 am, US Eastern Standard Time.


4.  Date plus hours, minutes, seconds and decimal fractions of a second
-----------------------------------------------------------------------

The number of seconds is followed by a dot and one or more digits
representing a decimal fraction of a second.  An adopting standard must
specify both the minimum and the maximum number of digits, as described
earlier.

If times are expressed in UTC, the format is:

               YYYY-MM-DDThh:mm:ss.sZ

Example:       1994-11-05T13:15:30.45Z

If times are expressed in local time, together with a time zone offset,
the format is:

               YYYY-MM-DDThh:mm:ss.s+hh:mm
or:
               YYYY-MM-DDThh:mm:ss.s-hh:mm

Example:       1994-11-05T08:15:30.45-05:00

Both the examples in this section correspond to November 5, 1994,
8:15:30.45 am, US Eastern Standard Time.


References
==========

[ISO 8601] "Data elements and interchange formats -- Information
interchange -- Representation of dates and times", ISO 8601:1988(E),
International Organization for Standardization, June, 1988.

[KUHN] "A Summary of the International Standard Date and Time Notation",
Markus Kuhn, <http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html>,
1996-11-05.

[NEWMAN] "Date and Time on the Internet", Chris Newman,
<draft-newman-datetime-01.txt>, January 1997.

------------------------------------------------------------------------
Misha Wolf            Email: misha.wolf at reuters.com     85 Fleet Street
Standards Manager     Voice: +44 171 542 6722           London EC4P 4AJ
Reuters Limited       Fax  : +44 171 542 8314           UK

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