DTV12 — The mythical 'weeks scale'

DTV defines the indefinite 'weeks scale' in clause 12.2 as follows:

Definition: indefinite time scale of granularity 'week' and of 'calendar week' time points

Note: No special meaning is assigned to the indices of calendar weeks on the week scale. Therefore, no index origin element or index origin value is specified for this time scale.

It then defines calendar week as follows:

Definition: time point that is on the weeks scale and that is defined by a given calendar as 7 consecutive calendar days

Note: ISO 8601 adds “starting on a Monday” to this definition. This vocabulary drops that phrase because it is culture-specific.

The net effect of these is that weeks are some sequences of 7 days that are determined by a calendar. We don’t know where any such sequence begins, or what day-of-week it begins with. There is no significance to the indices because none of them is defined to refer to any particular point in time. So, DTV does not define a specific ' weeks scale' at all.

Now, clause 12.1 says: "References to specific weeks are by week of year coordinate. This specification follows [ISO 8601] in defining 'Monday' as the first day of the week." This contradicts the above. But it does confirm that the finite 'year of weeks' scale is the only well-defined scale whose granularity is a week.

Then in 12.4 we find this entry:

year week coordinate indicates time point sequence

Definition: the Gregorian year coordinate and the week of year coordinate of year week coordinate jointly specify a time point sequence of Gregorian days

Note: Unlike other time coordinates, this one indicates a time point sequence, not a time point. This is because a year week coordinate means a sequence of calendar days rather an individual time point on some time scale.

So a 'year week coordinate' does not refer to a 'week' on any 'weeks scale' . Now, since it does not indicate any time point, a year-week coordinate is NOT a time coordinate.

The presented model is incomplete and inconsistent. The underlying model anchors a weeks scale to Gregorian days – every instance of a Gregorian day instantiates a particular day-of-week; and the relationship to Gregorian years is dependent on choosing Monday as the first day of week. It is absolutely necessary to anchor some day-of-week to some event or time interval, in order to have any idea which Gregorian days are Mondays. Somewhere in the text, it is mentioned that January 1, 2000 is a Saturday. (More useful is the fact that January 1, 1601 is a Monday.) And that, together with the assertion that Monday is the first day of a week-of-year, defines a weeks scale, except for assigning an index to the week containing January 1, 2000 (or 1601).

The underlying problem here was the unwillingness of the FTF to commit to Monday as the first day of the week, as indicated in the cited Note. The assertion in 12.1 did not represent consensus of the RTF. As a consequence, the Week Calendar Vocabulary, and most of the terms introduced in the section, are now prefixed by “ISO” to distinguish them from weeks calendars that choose other conventions for the first day of the week. At the same time, the neutral concepts ‘calendar week’ and ‘week period’ are retained and moved to Clause 10 to support the original purpose of allowing other choices for first day of week.
Establishing Monday as day of week 1 enables the specification of a reference time period for an index origin member for the indefinite weeks scale, choosing Monday, January 3, 2000, with an index consistent with the Gregorian day numbering.
Aligning the Gregorian calendar with the weeks calendar eliminates the need for the verb concept ‘year week coordinate indicates time point sequence’ and the related ‘starting week day’ idea, which are deleted. In its place, we create the ‘starting week’ concept, which is parallel to ‘starting day’. This enables the correct axioms (Necessities) for the year of weeks and year of weekdays scales.
Some related errors in terminology or arithmetic are also corrected.
The RTF determined in resolving Issue 19525 that the definition of ‘starting day’ should be functional and the calculation should be a Necessity. The same idea is applied to ‘starting week’.
Issue 19034 recommended editorial corrections to the terms for day of week time points. These are included in the modifications to the (ISO) day of week entry below.
Issue 19526 asked for corrections to the description of ‘starting weekday’, which this resolution deletes. But the definition of ‘starting week’ requires the notion ‘first Thursday’, which was embedded in the ‘starting week day’ concept. So the revised text carries the intent of Issue 19526 forward.
The resolution to Issue 19645 modifies the entry for the year of weekdays scale and incorporates text changes related to this issue. It also adds the concept ISO week-based year, which is mentioned in the revised introductory text below.
The resolution to Issue 19650 deletes section 12.5. Nomenclature changes in 12.5 that are related to this issue are therefore omitted below.