YYYYWwwD

YYYYWwwD is a compact date-encoding scheme used in scheduling, data interchange, and file naming. It encodes a calendar date by concatenating a four-digit year, the literal character W, a two-digit ISO week number, and a one-digit day-of-week indicator. The day-of-week uses the ISO convention, where 1 corresponds to Monday and 7 to Sunday. The result is an eight-character string such as 2024W351, which represents Monday of week 35 in 2024.

The format is derived from the ISO 8601 week-date system, which defines a year by ISO weeks rather than calendar months. The compact form is advantageous in contexts where space is at a premium or where lexicographic ordering should reflect chronological order. Because the components are fixed-length, YYYYWwwD strings sort naturally in ascending order for increasing dates.

Parsing and interpretation follow a straightforward rule set. An valid string must have length eight, with the fifth character being the letter W. The first four characters encode the year (0000 to 9999), the sixth and seventh characters encode the ISO week number (01 to 53), and the eighth character encodes the day of the week (1 to 7). For example, 2024W351 decodes to the Monday (1) of ISO week 35 in the year 2024. Week 53 is possible in certain years, and day numbers map to Monday through Sunday accordingly.

Limitations include uneven support across software libraries and potential ambiguity near week-year boundaries. It is most effective for fixed-length data fields and batch-processing workflows where ISO week semantics are desired. See also ISO week-date and date formatting conventions.