RE: XPath2 Type Promotion

Caroline:
You asked:
> So, which one is correct?  When converting an xs:decimal to an
xs:double, > should we go trough xs:float?

This addressed at the bottom of the paragraph following the second table
in 6.2, which says:

"As far as possible, the promotions should be done in a single step.
Specifically, when a decimal is promoted to a double, it must not be
converted to a float and then to double, as this risks loss of
precision."

All the best, Ashok
> -----Original Message-----
> From: public-qt-comments-request@w3.org [mailto:public-qt-comments-
> request@w3.org] On Behalf Of Caroline Rioux
> Sent: Monday, June 16, 2003 4:19 AM
> To: public-qt-comments@w3.org
> Subject: XPath2 Type Promotion
> 
> 
> Hi,
> 
> I've noticed an inconsistency in defining type promotion for XPath 2.
> 
> In F&O 6.2 Operators on Numeric Values, we have that xs:decimal can be
> promoted to xs:float, and xs:float can be promoted to xs:double :
> 
> -- "If the two operands are not of the same type, subtype substitution
and
> type promotion may be used to obtain two operands of the same type.
> Appendix B of [XQuery 1.0: An XML Query Language] describes the
semantics
> of these operations in detail.
> 
> 1. Subtype substitution: A derived type may substitute for its base
type.
> In particular, xs:integer may be used where xs:decimal is expected.
> 
> 2. Type promotion: xs:decimal may be promoted to xs:float, and
xs:float
> may be promoted to xs:double." --
> 
> However, Appendix B of [XQuery 1.0: An XML Query Language] seems to
allow
> for xs:decimal to be promoted directly to xs:double, without going
trough
> xs:float :
> 
> -- "The following type promotions are permitted:
> 
> 1. A value of type xs:float (or any type derived by restriction from
> xs:float) can be promoted to the type xs:double. The result is the
> xs:double value that is the same as the original value. This kind of
> promotion may cause loss of precision.
> 
> 2. A value of type xs:decimal (or any type derived by restriction from
> xs:decimal) can be promoted to either of the types xs:float or
xs:double.
> The result is the value of the target type that is closest to the
original
> value." --
> 
> Note that also in F&O 6.2 :
> 
> -- "For this operation, xs:int must be converted to xs:double. This
can be
> done, since by the rules above: xs:int can be substituted for
xs:integer,
> xs:integer can be promoted to xs:decimal, xs:decimal can be promoted
to
> xs:float, and xs:float can be promoted to xs:double. As far as
possible,
> the promotions should be done in a single step. Specifically, when a
> decimal is promoted to a double, it must not be converted to a float
and
> then to double, as this risks loss of precision." --
> 
> [As a side note, shouldn't that say "xs:integer can be substituted for
> xs:decimal" instead of "xs:integer can be promoted to xs:decimal"?]
> 
> So, which one is correct?  When converting an xs:decimal to an
xs:double,
> should we go trough xs:float?
> 
> Thanks,
> Caroline
> 
> --
> Caroline Rioux, Software Engineer           +44-1865-203192
> DecisionSoft Limited
http://www.decisionsoft.com
> XML Development and Services
>

Received on Monday, 16 June 2003 10:55:11 UTC