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Understanding ISO 8601 date and time representation formats. Tex Texin [email protected] XenCraft. Objectives for this session. ISO 8601:1988 is updated in 2000. What is in ISO 8601:2000? Are there potential pitfalls in using ISO 8601, especially for internationalization?

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Presentation Transcript
objectives for this session
Objectives for this session
  • ISO 8601:1988 is updated in 2000.
  • What is in ISO 8601:2000?
  • Are there potential pitfalls in using ISO 8601, especially for internationalization?
  • If so, are there workarounds?
agenda
Agenda

Brief Overview of ISO 8601

Problem Areas

Solutions

iso 8601 2000 overview
ISO 8601:2000 Overview
  • Dates
    • Calendar dates
    • Ordinal dates
    • Week dates
  • Time of day
    • Local vs. Coordinated Universal Time (UTC)
    • Combined date and time
  • Time-intervals
    • Recurring time-intervals
representing dates times durations and intervals
Representing dates, times, durations and intervals
  • Uses character representation
    • ISO/IEC 646 (ASCII), no spaces
  • Separators (Extended Format)
    • Hyphens, Colons, Solidus, Number sign
  • Truncation
    • Omission of higher order components
  • Reduced Precision
    • Omission of lower order components
  • Expansion- years < 0 or years > 9999
  • Fixed length fields using leading zeros
representing dates times durations and intervals6
Representing dates, times, durations and intervals
  • 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
  • Duration designators
    • Y, M, W, D, H, M, S may be used
    • M can be minute, month, or both
calendar dates
Calendar Dates
  • 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.
calendar week
Calendar week
  • Monday is day 1, Sunday is day 7.
  • Weeks are numbered 1- 52 or 1 - 53.
  • Week 1 includes the first Thursday of year.
    • Alternatively, Week 1 includes Jan 4.
  • Week 1 may include 3 days of last year.
    • Last week may include 3 days of next year.
representing dates
Representing dates
  • Calendar date
    • year, month, day number within month
  • Ordinal date
    • year, day number within year
  • Week date
    • year, week, number within week
iso 8601 2000 overview11
ISO 8601:2000 Overview
  • Dates
    • Calendar dates
    • Ordinal dates
    • Week dates
  • Time of day
    • Local vs. Universal Time Coordinated (UTC)
    • Combined data and time
  • Time-intervals
    • Recurring time-intervals
representing times
Representing times
  • Hours 00-24 (allowing midnight-midnight)
  • Minutes 00-59
  • Seconds 00-60 (allowing leap seconds)
  • Decimal fractions of hour, minute, second
  • Local and Universal (UTC) time
combined date and time
Combined date and time
  • “T” indicates start of time
  • 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

iso 8601 2000 overview15
ISO 8601:2000 Overview
  • Dates
    • Calendar dates
    • Ordinal dates
    • Week dates
  • Time of day
    • Local vs. Universal Time Coordinated (UTC)
    • Combined data and time
  • Time-intervals
    • Recurring time-intervals
representing time intervals
Representing time-intervals
  • “P” indicates a duration (period)
  • 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.

representing time intervals17
Representing time-intervals
  • 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

recurring time intervals
Recurring time-intervals
  • 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
  • If # of recurrences is not provided, then the number is unbounded
  • “R” is used to indicate recurrence
examples of recurring time intervals
Examples of recurring time-intervals

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

benefits of iso 8601
Benefits of ISO 8601
  • Human-readable
  • Easy to use
  • Easy to parse, unambiguous
  • Easy to sort
  • Many date-time schemes exist, a standard is needed
agenda21
Agenda

Brief Overview of ISO 8601

Problem Areas

Solutions

ambiguities
Ambiguities
  • Future leap seconds are unpredictable

Is 2010-03-31T23:59:60Z valid?

  • Year, month, minute have varying sizes

P1M = P28D or P29D or P30D or P31D

  • Mismatched precision

1985W50 <= 1985W501?

  • Truncation opens the door for Y2K issues
  • Variations of 8601 exist in practice
    • Julian, Gregorian, Emperor...
ambiguities23
Ambiguities
  • 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.)

  • Addition is not commutative or associative

2001-03-30 + P1D + P1M = 2001-04-30

2001-03-30 + P1M + P1D = 2001-05-01

  • Subtraction is not the inverse of Addition
  • Precision of decimal fractions can vary
conversions
Conversions
  • Gregorian calendar adopted at different times around the world
  • Most calendars do not include year 0.
  • 8601 extends leap years into the past, other calendars do not.
  • 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
conversions25
Conversions
  • Laws determining daylight savings time change continually
  • Difficult to know local time offsets.
agenda26
Agenda

Brief Overview of ISO 8601

Problem Areas

Solutions

solutions
Solutions
  • Mutual Agreements
  • Referencing other standards and implementations
    • e.g. Java
  • Standards employing 8601 may need to introduce rules or constraints
    • e.g. XML Schema
  • Restrict use of 8601 formats
acknowledgements
Mark Davis (IBM)

www.macchiato.com/unicode/timeIntervals.htm

W3C Internationalization working and interest groups

Resources

ISO’s web page to order the standard: http://www.iso.ch/cate/d26780.html

Mail list: [email protected]

Links:

groups.yahoo.com/group/ISO8601/files/pdf_link.htm

http://aa.usno.navy.mil/faq/docs/UT.html

Acknowledgements
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