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Re: What are the characteristics of a good type system for XML


characteristics of a good system
Jeni Tennison scripsit:

> John brought up the issue of types that don't have total ordering. The
> lack of total ordering of durations and date/times with or without
> timezones has been a real pain in XPath 2.0 because for optimisation
> purposes you really need just one of $a = $b or $a != $b to be true.
> You could, of course, introduce three-valued logic to cope with the
> ambiguity, but I'd be interested if anyone had any other bright ideas.

IMHO the whole notion of times without zones is so much $*@(.  The value
type should be just UTC instants or periods, and it should be possible
to specialize the type Date to the type ESTDate, or America_New_York_Date,
supplying the default timezone as part of the type.

The problem of incommensurable durations (which is longer, 60 sec or 1 min?)
is much more serious, and I don't see that anything can reliably be done
about it.  Durations are simply not totally-ordered.

-- 
"Do I contradict myself?                        John Cowan
Very well then, I contradict myself.            jcowan@r...
I am large, I contain multitudes.               http://www.ccil.org/~cowan
        --Walt Whitman, _Leaves of Grass_       http://www.reutershealth.com

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