Hmm, am I understanding you explaination?
Here is a rational expression:
9/4 * 4/3 = 3
With floats this ends up being close, but with rounding errors.
2.25*1.333333 2.9999992500000001
If this is expressed as a product of 2.25b * 1.333333d the result would be an inexact value. A binary number would be returned, instead of the decimal number 3.
Correct.
Where is Tim's "numeric context" located?
In his mind. :-) I believe it is typically global per thread, but that's up to the langage binding. A Java binding for Cowlishaw's decimals apparently requires passing in a context as a third argument on each operation.
M.-A. Lemburg" suggested looking at the SQL specification for Decimal datatypes. A decimal type is also defined as a type in XML Schema. Since this is an XML datatype there isn't a definition for how these numbers are created.
Do these say anything about semantics under numeric operations? That would seem to be outside the realm of XML and possibly even outside SQL. So I'm not sure how these help.
NOTE: All ·minimally conforming· processors ·must· support decimal numbers with a minimum of 18 decimal digits (i.e., with a ·totalDigits· of 18). However, ·minimally conforming· processors ·may· set an application-defined limit on the maximum number of decimal digits they are prepared to support, in which case that application-defined maximum number ·must· be clearly documented. - http://www.w3.org/TR/xmlschema-2/#decimal
I followed the URL and found only external representation issues, nothing that can help us. --Guido van Rossum (home page: http://www.python.org/~guido/)