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Re: Negative values should be returned from seconds-from-dateTime()

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Fri, 1 Aug 2008 21:19:22 +0100
Message-ID: <ed77aa9f0808011319q76aa1578jaea772f33d9d0a17@mail.gmail.com>
To: "John Boyer" <boyerj@ca.ibm.com>
Cc: public-forms <public-forms@w3.org>

Hi John,

Damn...that means those time and date functions are *still* not
working correctly!

:)

Anyway, thanks for that, and you are exactly right.

Regards,

Mark

On Fri, Aug 1, 2008 at 9:11 PM, John Boyer <boyerj@ca.ibm.com> wrote:
>
> Hi Mark,
>
> I don't think the spec says that the sign of the difference should be
> removed.
>
> A difference can be positive or negative.
>
> The wording appears to take for granted that it is reasonably obvious to
> implementers that they should take the difference in a way that makes sense,
> i.e. that Jan. 1, 1970 midnight zulu time should be taken as the "origin" of
> the oriented time line, so that times *after* that will come out positive
> and times earlier will come out negative.  The difference suggested by the
> spec is (parameter - origin), converted to seconds.
>
> The second example in the spec shows a postivie value because
> '1970-01-01T00:00:00-08:00' is actually 8 hours *later* than midnight zulu
> time.
>
> Cheers,
> John M. Boyer, Ph.D.
> Senior Technical Staff Member
> Lotus Forms Architect and Researcher
> Chair, W3C Forms Working Group
> Workplace, Portal and Collaboration Software
> IBM Victoria Software Lab
> E-Mail: boyerj@ca.ibm.com
>
> Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer
> Blog RSS feed:
> http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw
>
>
>
>
> From: "Mark Birbeck" <mark.birbeck@webbackplane.com>
> To: public-forms <public-forms@w3.org>
> Date: 08/01/2008 06:02 AM
> Subject: Negative values should be returned from seconds-from-dateTime()
> ________________________________
>
>
>
> Hello all,
>
> I've been having a lot of fun :( trying to get the various date/time
> functions working in the Ubiquity XForms library, and most of the
> problems arise from timezone switching.
>
> Anyway, one of the tests for seconds-from-dateTime() involves a
> timezone, as follows:
>
>  Assert.areEqual(28800,
> evalXPath('seconds-from-dateTime("1970-01-01T00:00:00-08:00")').numberValue());
>
> This test is based on an example in section 7.9.6 of the XForms 1.1 spec.
>
> My question is, why is the example saying that it should be a positive
> number? It's true that the spec says:
>
>  "...the return value is equal to the number of seconds difference..."
>
> which would imply making the number positive -- so the result is
> correct according to the spec. But I wonder what we gain by *losing*
> the sign of the result.
>
> The problem is further compounded when you use this function with the
> complementary seconds-to-dateTime(). Nothing says that
> seconds-to-dateTime() should _not_ take a negative value, so the
> problem we have is that the following pair of calls does not give you
> back what you started with:
>
>  seconds-from-dateTime(seconds-to-dateTime(-28800))
>
> I.e, the result according to the spec is 28800, when it could easily be
> -28800.
>
> I think that the fix is to simply change the example in the spec,
> which would send a clear signal to implementers:
>
>  Example:
>
>  seconds-from-dateTime('1970-01-01T00:00:00Z')
>  returns 0
>
>  seconds-from-dateTime('1970-01-01T00:00:00-08:00')
>  returns -28800
>
> Note that the Ubiquity XForms unit tests for this are currently
> passing because I've set the functions to return a negative number.
> Obviously I'll change that if need be, but I'll see what points come
> up on this discussion first.
>
> Regards,
>
> Mark
>
> --
> Mark Birbeck, webBackplane
>
> mark.birbeck@webBackplane.com
>
> http://webBackplane.com/mark-birbeck
>
> webBackplane is a trading name of Backplane Ltd. (company number
> 05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
> London, EC2A 4RR)
>
>
>
>



-- 
Mark Birbeck, webBackplane

mark.birbeck@webBackplane.com

http://webBackplane.com/mark-birbeck

webBackplane is a trading name of Backplane Ltd. (company number
05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
London, EC2A 4RR)
Received on Friday, 1 August 2008 20:20:01 UTC

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