Re: Timezones in get-hours-from-dateTime etc.

Here is a suggestion for a supplemental convenience feature
that will hopefully make everybody happy:

get-XXX-from-dateTime accepts an optional second argument 'timezone'
    such that

	get-hours-from-dateTime($dt, $tz)

    is equivalent to:

	get-hours-from-dateTime(adjust-dateTime-to-timezone($dt, $tz))

This way the following expression returns the normalized UTC component:

	get-hours-from-dateTime($dt, 0)

      (Note: using the duration notation proposed by Michael Kay)

while the following expression returns the component as specified initially
(i.e. using the timezone that was specified or implicit when
   the date/time object $dt was created):

	get-hours-from-dateTime($dt)

to get the component in the implicit timezone:
(not necessarily the same as above)

	get-hours-from-dateTime($dt, implicit-timezone())



-- 
Xavier FRANC
>  http://lists.w3.org/Archives/Public/public-qt-comments/2003Sep/0124.html
> 
> suggested that the date/time component extraction functions (for example,
> get-hours-from-dateTime()) should return components of the localized time,
> rather than the normalized time.
> 
> (Terminology: localized time = the time in the timezone represented by the
> timezone component of the value; normalized time = the same instant of time
> represented in timezone UTC)
> 
> On reflection, I'm inclined to agree with Xavier: I think we have got this
> wrong. The date/time is presented in localized form when converting it to a
> string, and when using the XSLT format-dateTime() family of functions. I
> think it will be less confusing if we consistently present date/time values
> in the localized form, and require users to use adjust-X-to-timezone if they
> want something different.
> 
> Currently, if you want the components of the localized value, you have to
> call adjust-dateTime-to-timezone() with () as the second argument, and then
> call get-hours-from-dateTime. 
> 
> With this change, a user who wanted components of the normalized value would
> use adjust-dateTime-to-timezone() to adjust the timezone to UTC, and then
> extract the component values.
> 
> Specifically (in XQuery syntax):
> 
> let $utc := xdt:dayTimeDuration("PT0H"),
>     $ndt := adjust-dateTime-to-timezone($in, $utc) return
>     get-hours-from-dateTime($ndt)
> 
> We might also want to consider changing the default for the second argument
> of adjust-X-to-timezone() so it adjusts to UTC, since adjusting to the local
> timezone can easily be achieved by supplying implicit-timezone() as the
> second parameter. Alternatively, if my proposal on durations is accepted,
> then adjust-dateTime-to-timezone($in, 0) will return the normalized value.
>

Received on Friday, 3 October 2003 08:37:43 UTC