understanding iso 8601 date and time representation formats tex texin [email protected] xencraft

Understanding ISO 8601 date and time representation formats

Understanding ISO 8601 date and time representation formats

Tex [email protected]

21st International Unicode Conference 2 Dublin, Ireland, May 2002

Objectives for this sessionObjectives 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?


Brief Overview of ISO 8601

Problem Areas

Solutions


Problem Areas

Solutions

AgendaAgenda


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

ISO 8601:2000 OverviewISO 8601:2000 Overview


Representing dates, times, durations and intervalsRepresenting 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 intervalsRepresenting 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 DatesCalendar 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 weekCalendar 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 datesRepresenting dates

Calendar date– year, month, day number within month

Ordinal date– year, day number within year

Week date– year, week, number within week


Representing datesRepresenting datesDate Basic Format Extended

FormatCalendar date YYYYMMDD

19850412YYYY-MM-DD1985-04-12

Truncated - - MMDD- - 0412

- - MM-DD- - 04-12

Expanded ±YYYYYYMMDD±0019850412

±YYYYYY-MM-DD±001985-04-12

Ordinal date YYYYDDD1985102

YYYY-DDD1985-102

Week date YYYYWwwD1985W155

YYYY-Www-D1985-W15-5

ReducedPrecision

YYYYWww1985W15

YYYY-Www1985-W15



Time of day– Local vs. Universal Time Coordinated (UTC)– Combined data and time




Representing timesRepresenting 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


Representing timesRepresenting times

Time Basic Format ExtendedFormat

Local time hhmmss232050

hh:mm:ss23:20:50

Decimalfractions

hhmmss,ss232050,5

hh:mm:ss,ss23:20:50,5

Universal time hhmmssZ232050Z

hh:mm:ssZ23:20:50Z

Local time offsetUTC

hhmmss±hhmm232050+0100

hh:mm:ss±hh:mm23:20:50+01:00


Combined date and timeCombined date and time

“T” indicates start of time Mix and match as needed:

Calendar dates + local timeYYYY-MM-DDThh:mm

Ordinal dates + UTC timeYYYY-DDDThh:mmZ

Week dates + offset from UTCYYYYWwwDThh:mm±hhmm



Time of day– Local vs. Universal Time Coordinated (UTC)– Combined data and time




Representing time-intervalsRepresenting 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

– durationsPnYnMnDTnHnMnS

P2Y10M15DT10H30M20S

2 Yr, 10 mon, 15 days, 10 hrs. 30 min. 20 sec.

P6W is a duration of 6 weeks.


Representing time-intervalsRepresenting time-intervals

The remaining 2 varieties– start time and durationYYYY-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 timePnYnMnDTnHnMnS/YYYY-MM-DDThh:mm:ss or

PYYYY-MM-DDThh:mm:ss/YYYY-MM-DDThh:mm:ss


Recurring time-intervalsRecurring 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


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-intervalsExamples of recurring time-intervals


Benefits of ISO 8601Benefits of ISO 8601

Human-readable Easy to use Easy to parse, unambiguous Easy to sort Many date-time schemes exist, a standard

is needed



Problem Areas

Solutions


Problem Areas

Solutions

AgendaAgenda


AmbiguitiesAmbiguities

Future leap seconds are unpredictableIs 2010-03-31T23:59:60Z valid?

Year, month, minute have varying sizesP1M = P28D or P29D or P30D or P31D

Mismatched precision1985W50 <= 1985W501?

Truncation opens the door for Y2K issues Variations of 8601 exist in practice– Julian, Gregorian, Emperor...


AmbiguitiesAmbiguities

Date arithmetic is not defined2001-03-30 + 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


ConversionsConversions

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


ConversionsConversions

Laws determining daylight savings time change continually

Difficult to know local time offsets.



Problem Areas

Solutions


Problem Areas

Solutions

AgendaAgenda


SolutionsSolutions

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


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

AcknowledgementsAcknowledgements


Questions

understanding iso 8601 date and time representation formats tex texin [email protected] xencraft

Documents

time n timeintervals

time n mix

n local

timeintervals n p

n seconds

n weeks

calendar week n

dates slide