1. Understanding ISO 8601 date and time representation formats Tex Texin Tex@I18nGuy.com XenCraft

2. 21st International Unicode Conference 2Dublin, Ireland, May 2002 Objectives for this session n ISO 8601:1988 is updated in 2000. n What is in ISO 8601:2000? n Are there potential pitfalls in using ISO 8601, especially for internationalization? n If so, are there workarounds?

3. 21st International Unicode Conference 3Dublin, Ireland, May 2002 Brief Overview of ISO 8601 Problem Areas Solutions Brief Overview of ISO 8601 Problem Areas Solutions Agenda

4. 21st International Unicode Conference 4Dublin, Ireland, May 2002 n Dates –Calendar dates –Ordinal dates –Week dates n Time of day –Local vs. Coordinated Universal Time (UTC) –Combined date and time n Time-intervals –Recurring time-intervals ISO 8601:2000 Overview

5. 21st International Unicode Conference 5Dublin, Ireland, May 2002 Representing dates, times, durations and intervals n Uses character representation –ISO/IEC 646 (ASCII), no spaces n Separators (Extended Format) –Hyphens, Colons, Solidus, Number sign n Truncation –Omission of higher order components n Reduced Precision –Omission of lower order components n Expansion- years 9999 n Fixed length fields using leading zeros

6. 21st International Unicode Conference 6Dublin, Ireland, May 2002 Representing dates, times, durations and intervals n Designators –P is time-interval designator –R is recurring time-interval designator –T indicates start of Time elements –W is week designator –Z is UTC designator n Duration designators –Y, M, W, D, H, M, S may be used –M can be minute, month, or both

7. 21st International Unicode Conference 7Dublin, Ireland, May 2002 Calendar Dates n Gregorian calendar –1875 is reference point –Common (365) and Leap (366) years –Leap is every 4th year except centennial years that are not integrally divisible by 400 –Gregorian is used even for years < 1582 (by mutual agreement). –Year 0000 is leap.

8. 21st International Unicode Conference 8Dublin, Ireland, May 2002 Calendar week n Monday is day 1, Sunday is day 7. n Weeks are numbered 1- 52 or 1 - 53. n Week 1 includes the first Thursday of year. –Alternatively, Week 1 includes Jan 4. n Week 1 may include 3 days of last year. –Last week may include 3 days of next year.

9. 21st International Unicode Conference 9Dublin, Ireland, May 2002 Representing dates n Calendar date –year, month, day number within month n Ordinal date –year, day number within year n Week date –year, week, number within week

10. 21st International Unicode Conference 10Dublin, Ireland, May 2002 Representing dates

11. 21st International Unicode Conference 11Dublin, Ireland, May 2002 n Dates –Calendar dates –Ordinal dates –Week dates n Time of day –Local vs. Universal Time Coordinated (UTC) –Combined data and time n Time-intervals –Recurring time-intervals ISO 8601:2000 Overview

12. 21st International Unicode Conference 12Dublin, Ireland, May 2002 Representing times n Hours 00-24 (allowing midnight-midnight) n Minutes 00-59 n Seconds 00-60 (allowing leap seconds) n Decimal fractions of hour, minute, second n Local and Universal (UTC) time

13. 21st International Unicode Conference 13Dublin, Ireland, May 2002 Representing times

14. 21st International Unicode Conference 14Dublin, Ireland, May 2002 Combined date and time n T indicates start of time n Mix and match as needed: Calendar dates + local time YYYY-MM-DDThh:mm Ordinal dates + UTC time YYYY-DDDThh:mmZ Week dates + offset from UTC YYYYWwwDThh:mm±hhmm

15. 21st International Unicode Conference 15Dublin, Ireland, May 2002 n Dates –Calendar dates –Ordinal dates –Week dates n Time of day –Local vs. Universal Time Coordinated (UTC) –Combined data and time n Time-intervals –Recurring time-intervals ISO 8601:2000 Overview

16. 21st International Unicode Conference 16Dublin, Ireland, May 2002 Representing time-intervals n P indicates a duration (period) n Intervals come in 4 varieties: –start and end times YYYY-MM-DDThh:mm:ss/YYYY-MM-DDThh:mm:ss –durations PnYnMnDTnHnMnS P2Y10M15DT10H30M20S 2 Yr, 10 mon, 15 days, 10 hrs. 30 min. 20 sec. P6W is a duration of 6 weeks.

17. 21st International Unicode Conference 17Dublin, Ireland, May 2002 Representing time-intervals n The remaining 2 varieties –start time and duration YYYY-MM-DDThh:mm:ss/PnYnMnDTnHnMnS or YYYY-MM-DDThh:mm:ss/PYYYY-MM-DDThh:mm:ss 1985-04-12T23:20:50/P0001-02-15T12:30:00 –duration and end time PnYnMnDTnHnMnS/YYYY-MM-DDThh:mm:ss or PYYYY-MM-DDThh:mm:ss/YYYY-MM-DDThh:mm:ss

18. 21st International Unicode Conference 18Dublin, Ireland, May 2002 Recurring time-intervals n Recurring time intervals are expressed by: –# of recurrences and start and end times –# of recurrences and a duration –# of recurrences & start time & a duration –# of recurrences & duration & end time n If # of recurrences is not provided, then the number is unbounded n R is used to indicate recurrence

19. 21st International Unicode Conference 19Dublin, Ireland, May 2002 Recurring with Start and End Times: Rn/YYYY-MM-DDThh:mm:ss/YYYY-MM-DDThh:mm:ss R12/1985-04-12T23:20:50/1985-06-25T10:30:00 Recurring with a duration: Rn/PnYnMnDTnHnMnS R12/P2Y10M15DT10H20M20S Recurring with a Start Time and duration: Rn/YYYY-MM-DDThh:mm:ss/PnYnMnDTnHnMnS R12/1985-04-12T23:20:50/P2Y2M15DT12H30M0S Examples of recurring time-intervals

20. 21st International Unicode Conference 20Dublin, Ireland, May 2002 Benefits of ISO 8601 n Human-readable n Easy to use n Easy to parse, unambiguous n Easy to sort n Many date-time schemes exist, a standard is needed

21. 21st International Unicode Conference 21Dublin, Ireland, May 2002 Brief Overview of ISO 8601 Problem Areas Solutions Brief Overview of ISO 8601 Problem Areas Solutions Agenda

22. 21st International Unicode Conference 22Dublin, Ireland, May 2002 Ambiguities n Future leap seconds are unpredictable Is 2010-03-31T23:59:60Z valid? n Year, month, minute have varying sizes P1M = P28D or P29D or P30D or P31D n Mismatched precision 1985W50 <= 1985W501? n Truncation opens the door for Y2K issues n Variations of 8601 exist in practice –Julian, Gregorian, Emperor...

23. 21st International Unicode Conference 23Dublin, Ireland, May 2002 Ambiguities n Date arithmetic is not defined 2001-03-30 + P1M = 2001-04-29 (Add 30 days) 2001-03-30 + P1M = 2001-04-30 (Add 1 mon.) n Addition is not commutative or associative 2001-03-30 + P1D + P1M = 2001-04-30 2001-03-30 + P1M + P1D = 2001-05-01 n Subtraction is not the inverse of Addition n Precision of decimal fractions can vary

24. 21st International Unicode Conference 24Dublin, Ireland, May 2002 Conversions n Gregorian calendar adopted at different times around the world n Most calendars do not include year 0. n 8601 extends leap years into the past, other calendars do not. n Dates without times are often not qualified by time zone. –Time zones (currently) go from -13 to +12 –So the date could be +/- 1 day

25. 21st International Unicode Conference 25Dublin, Ireland, May 2002 Conversions n Laws determining daylight savings time change continually n Difficult to know local time offsets.

26. 21st International Unicode Conference 26Dublin, Ireland, May 2002 Brief Overview of ISO 8601 Problem Areas Solutions Brief Overview of ISO 8601 Problem Areas Solutions Agenda

27. 21st International Unicode Conference 27Dublin, Ireland, May 2002 Solutions n Mutual Agreements n Referencing other standards and implementations –e.g. Java n Standards employing 8601 may need to introduce rules or constraints –e.g. XML Schema n Restrict use of 8601 formats

28. 21st International Unicode Conference 28Dublin, Ireland, May 2002 n Mark Davis (IBM) www.macchiato.com/unicode/timeIntervals.htm n W3C Internationalization working and interest groups Resources n ISOs web page to order the standard: http://www.iso.ch/cate/d26780.html http://www.iso.ch/cate/d26780.html n Mail list: ISO8601@yahoogroups.com n Links: groups.yahoo.com/group/ISO8601/files/pdf_link.htm http://aa.usno.navy.mil/faq/docs/UT.html Acknowledgements

29. 21st International Unicode Conference 29Dublin, Ireland, May 2002 Questions