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

From: John Boyer <boyerj@ca.ibm.com>
Date: Fri, 1 Aug 2008 13:11:24 -0700
To: "Mark Birbeck" <mark.birbeck@webbackplane.com>
Cc: public-forms <public-forms@w3.org>
Message-ID: <OFD8B41B21.868E1668-ON88257498.006E7320-88257498.006EE89D@ca.ibm.com>
Hi Mark,

I don't think the spec says that the sign of the difference should be 

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 

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: 

"Mark Birbeck" <mark.birbeck@webbackplane.com>
public-forms <public-forms@w3.org>
08/01/2008 06:02 AM
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:


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:


I.e, the result according to the spec is 28800, when it could easily be 

I think that the fix is to simply change the example in the spec,
which would send a clear signal to implementers:


  returns 0

  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.



Mark Birbeck, webBackplane



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 20:12:11 UTC

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