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RE: patterns and restrictions

• To: <max@m...>,<xml-dev@l...>
• Subject: RE: patterns and restrictions
• From: "Michael Kay" <michael.h.kay@n...>
• Date: Wed, 17 Dec 2003 19:16:25 -0000
• Importance: Normal
• In-reply-to: <3FE07653.4050000@m...>
• Reply-to: <michael.h.kay@n...>

> 
> Does the following allow 'abc' as a valid value?
> 
> <xs:simpleType name="MyDouble">
>         <xs:restriction base="xs:double">
>             <xs:pattern value="[^N].*"/>
>         </xs:restriction>
> </xs:simpleType>

No, it doesn't. The value must be a double, and its lexical
representation must conform to the pattern. Actually I think every
double will conform to this pattern, so the pattern is redundant.

Using patterns to constrain values other than strings is questionable
though. Constraining an input document to contain a number such as
"23.50" rather than "23.5" puts an unnecessary burden on anyone
generating these documents, especially if they are using XSLT or XQuery
to do it. It's the value that matters, not its representation.

Michael Kay


> 
> We had been working under the belief that, via restriction - patterns 
> from both the new datatype and the original one are 'And'ed together. 
> i.e - the above datatype would only allow values valid for a double - 
> with the exception of NaN.
> 
> However, we've read somewhere today that whenever a pattern facet is 
> evaluated - it is evaluated against a string.  Though XMLSpy 
> and Xerces 
> both reject 'abc', is this an added bonus? Should we rely on this, or 
> should we define patterns in these instances to be tighter?
> 
> My suspiscion is that our original belief was correct, patterns are 
> inherited also, but we would appreciate some confirmation of this.
> 
> thanks
> 
> Max
> 
> 
> 
> 
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