Understanding%20ISO%208601%20date%20and%20time%20representation%20formats

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Understanding ISO 8601 date and time
representation formats

• Tex Texin
• Tex_at_I18nGuy.com
• XenCraft

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Objectives for this session

• ISO 86011988 is updated in 2000.
• What is in ISO 86012000?
• Are there potential pitfalls in using ISO 8601,
  especially for internationalization?
• If so, are there workarounds?

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Agenda
Brief Overview of ISO 8601 Problem
Areas Solutions
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ISO 86012000 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

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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 lt 0 or years gt 9999
• Fixed length fields using leading zeros

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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

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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 lt 1582 (by
  mutual agreement).
• Year 0000 is leap.

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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.

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Representing dates

• Calendar date
• year, month, day number within month
• Ordinal date
• year, day number within year
• Week date
• year, week, number within week

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Representing dates
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ISO 86012000 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

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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

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Representing times
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Combined date and time

• T indicates start of time
• Mix and match as needed
• Calendar dates local time
• YYYY-MM-DDThhmm
• Ordinal dates UTC time
• YYYY-DDDThhmmZ
• Week dates offset from UTC
• YYYYWwwDThhmmhhmm

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ISO 86012000 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

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Representing time-intervals

• P indicates a duration (period)
• Intervals come in 4 varieties
• start and end times
• YYYY-MM-DDThhmmss/YYYY-MM-DDThhmmss
• durations
• PnYnMnDTnHnMnS
• P2Y10M15DT10H30M20S
• 2 Yr, 10 mon, 15 days, 10 hrs. 30 min. 20 sec.
• P6W is a duration of 6 weeks.

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Representing time-intervals

• The remaining 2 varieties
• start time and duration
• YYYY-MM-DDThhmmss/PnYnMnDTnHnMnS or
• YYYY-MM-DDThhmmss/PYYYY-MM-DDThhmmss
• 1985-04-12T232050/P0001-02-15T123000
• duration and end time
• PnYnMnDTnHnMnS/YYYY-MM-DDThhmmss or
• PYYYY-MM-DDThhmmss/YYYY-MM-DDThhmmss

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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

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Examples of recurring time-intervals
Recurring with Start and End Times Rn/YYYY-MM-DDT
hhmmss/YYYY-MM-DDThhmmss R12/1985-04-12T2320
50/1985-06-25T103000 Recurring with a
duration Rn/PnYnMnDTnHnMnS R12/P2Y10M15DT10H20M20
S Recurring with a Start Time and
duration Rn/YYYY-MM-DDThhmmss/PnYnMnDTnHnMnS R1
2/1985-04-12T232050/P2Y2M15DT12H30M0S
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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

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Agenda
Brief Overview of ISO 8601 Problem
Areas Solutions
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Ambiguities

• Future leap seconds are unpredictable
• Is 2010-03-31T235960Z valid?
• Year, month, minute have varying sizes
• P1M P28D or P29D or P30D or P31D
• Mismatched precision
• 1985W50 lt 1985W501?
• Truncation opens the door for Y2K issues
• Variations of 8601 exist in practice
• Julian, Gregorian, Emperor...

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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

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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

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Conversions

• Laws determining daylight savings time change
  continually
• Difficult to know local time offsets.

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Agenda
Brief Overview of ISO 8601 Problem
Areas Solutions
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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

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Acknowledgements

• Mark Davis (IBM)
• www.macchiato.com/unicode/timeIntervals.htm
• W3C Internationalization working and interest
  groups
• Resources
• ISOs web page to order the standard
  http//www.iso.ch/cate/d26780.html
• Mail list ISO8601_at_yahoogroups.com
• Links
• groups.yahoo.com/group/ISO8601/files/pdf_link.htm
• http//aa.usno.navy.mil/faq/docs/UT.html

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Questions
?