ISO 8601 week days
ISO 8601 DATE and TIME standard is edited by the International Organization for Standardization (ISO) and specifies Data elements and interchange formats for Representation of dates and times based on the gregorian calendar system. Main intent is a commonly accepted system for ordering date and time values from the most to the least significant and from the largest (the year) to the smallest (the second).
ISO YEAR definition
Following the ISO YEAR Standard the ISO YEARS have 4 digits and can also extended with a prefix – or + , for example to express years before our gregorian year zero.
ISO WEEKs and ISO WEEK-Numbers Definition
Week dates can be format in different ways – for example the
YYYY-Www or YYYYWww form or with additional Weekday Number “D”
YYYY-Www-D or YYYYWwwD
“YYYY” stands for the ISO year which is exatctly not the same as a gregorian calendar year. “Www” means the week number prefixed by the letter ‘W‘, from W01 through W53. “D” is the weekday number, from 1 through 7, beginning with Monday and ending with Sunday. This form is popular in the international scheduling and time planning.
Example of ISO conform Week-DATE: 2010-01-03 is written “2009-W53-7”
ISO week numbers year starts always at Monday as first day of week 01 and ends at the Sunday before the new ISO year. ISO Years have 52 or 53 full weeks (each with 7 days). Only for Thursdays, the ISO week-numbering year number is always equal to the gregorian calendar year number. In each other week day as beginning day of the Calendar week year the ISO calendar tends to be slightly different.
