Time Interval Strings

Some features of TWiki, such as searches, permit the specification of time intervals. A time interval is a period of time, such as "1337 to 1451" (the Hundred Years War) or "9th February 2005 to 26th March 2005" (the Christian season of Lent).

The recognised format is a restricted interpretation of the ISO standard 8601.

A string is accepted as a valid time interval string if it conforms to the following grammar:

interval ::= date
           | date '/' date
           | 'P' duration '/' date
           | date '/' 'P' duration
           ;

date ::= year ('-' month ('-' day ('T' hour (':' minute (':' second)))))
       | '$today'
       | '$now'
       ;

duration ::= NUM unit
           | duration NUM unit
           ;

unit ::= 'y' | 'm' | 'w' | 'd' | 'h' | 'M' | 'S'

year, month, day, hour, minute, second ::= NUM

An incompletely specified date will be completed by including as much time as possible.

For example, if the start of a date range is specified by just a year, e.g. 1999/2006, it will be interpreted as starting at January 1st 1999, at zero hours zero minutes zero seconds. Similarly for the end of the range; 2006 will be interpreted as the last second of 2006.

If only one date is specified (e.g. the interval string is 1999) it will be treated as if the same date were the start and the end i.e. 1999-1999. Thus 1999 is interpreted as the whole of the year 1999.

You write	You mean
2003	the whole year 2003
2003-03-28T/2003-05-15	from March 28th to May 15th of the year 2003
P3w/$today	three weeks until today
2003-12-12	12th Dec 2003, from 0:00 to 23:59:59
2003	any time in the year 2003
2003/P20w	the first 20 weeks of the year 2003
P20w/2003	the last 20 weeks of the year 2003
$today	any second during the present day
P2d/$today	today and yesterday
P1d/$now	the last 24 hours
$now/P50y	the next 50 years

Further examples can be seen here.

Limitations

If you are entering a date at both ends of the time interval string, the end date must include all leading fields, even if these are the same as in the start date. This limitation forms a proper restriction to the ISO8601 standard. i.e. ISO8601 specifies that 2003-12-12/14 means 12th Dec 2003 00:00 to 14th Dec 2003 23:59:59. However this shorthand is not supported by TWiki and must be written as 2003-12-12/2003-12-14