On Thu, Nov 5, 2009 at 10:23 PM, C. M. Sperberg-McQueen
<cmsmcq(_at_)blackmesatech(_dot_)com> wrote:
As far as I can tell (but I am not a numerical analyst), every
number expressible with a finite sequence of binary digits
can also be expressed with a finite sequence of decimal digits
(ten being divisible by two), so every number in the value
space of xs:double also makes an appearance in the value
space of xs:decimal. (Recall though that for simplicity XSD
treats all primitive value spaces as disjoint, so a sentence
like "The value space of xs:double is a subset of the value
space of xs:decimal" would provoke howls of pain from some
quarters.)
I hope I'm taking this not too far off from this list's topic, but
one should see the point "some quarters" are trying to uphold.
While it is not debatable that the set of real numbers represented
by xs:double is a subset of those represented by xs:decimal, a
distinction must be made w.r.t. their respective value spaces
which happen to be part of different *data type* definitions. In
XML, data typing is associated with representation issues
such as facets; in programming languages distinctions are
being made by different (arithmetic) operations being applicable,
or by conversions, etc.
-W
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