Re: date:date-time()

On Thursday 05 January 2006 12:30, Jeremy Kloth wrote:
> The current spec for date-time() allows for either UTC (Z) or local
> (-/+HH:MM) timezones.  If an implementation decides to use UTC there is no
> way to determine what the local offset would be.  This also chains to the
> rest of the functions as they then operate only on the UTC date/time.
>
> There should be some way of working with both the UTC and offset-based
> timezones.  Some ideas:
>
> - mandate that date:date-time() allows uses the offset notation;
>
> - have date:date-time() grow an optional boolean argument that specifies
> with to return the timezone in UTC or offset notation;
>
> - add an additional function, say date:convert-timezone(), that switches
> from offset to UTC notation;
>
> - add an addition function, date:utc-offset(), that returns a duration that
> represents the offset of the given date/time or current time.
>
> As it stands, the lack of control, by the user, over which format can cause
> confusion.  For example, there was a comment on #4suite whether
> day-in-year() was working because it was returning 1 day later than it
> would have been if it was in local time.
>
> This issue needs to be resolved in some fashion, i'm leaning towards the
> optional argument to date:date-time(), that when present and true, UTC
> notation is used, otherwise offset notation.  I choose offset notation as
> that is what is implemented by the Javascript versions and by the majority
> of the processors (all except 4Suite which defaults to 'Z').

Just responding to myself to add some followup research.  The "status quo" wrt 
the default timezone is the offset (-/+HH:MM) notation.  The reference 
implementations as well as libxslt, saxon and xalan all return with that for 
those functions that have a "default" value of the current time.  4Suite is 
the odd-man-out in this one.

Some questions for the users of EXSLT Dates and Times out there:

- is the return value of "local time" what you are expecting?

- is "current time" just not used and therefore the TZ not an issue?  In other 
words, only preexisting date/time strings are used.

- are dates/times in UTC not really important (or simply unused)?

OK, so now I'm going with the notion that date:date-time() ALWAYS returns 
"local time".  Also an additional function, date:convert-timezone() is added 
to handle the need for UTC (and other) timezones.  In template syntax:

<xsl:call-template name="date:convert-timezone">
   <xsl:with-param name="date-time" select="string" />
   <xsl:with-param name="timezone" select="string" />
</xsl:call-template>

where date-time is either xs:dateTime or xs:time and timezone is either 'Z' or 
'+/-HH:MM'.

Here is hoping to having some constructive discussion...

-- 
Jeremy Kloth
http://fourthought.com/
http://4suite.org/