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Re: XML Schema quiz on default values

From: Michael Kay <mike@saxonica.com>
Date: Fri, 24 Aug 2012 09:07:50 +0100
Message-ID: <50373656.8000506@saxonica.com>
To: xmlschema-dev@w3.org
I've tried to explain it twice and I'm having difficulty finding a third 
way to express it.

The relevant rules are Validation Rule: Element Locally Valid (Element) 
clause 5 which says

5 The appropriate case among the following is true:
5.1 If D has a {value constraint}, and E has neither element nor 
character [children], and E is not ˇnilledˇ with respect to D , then all 
of the following are true:
5.1.1 If E's ˇgoverning type definitionˇ is an ˇinstance-specified type 
definitionˇ, then D.{value constraint} is a valid default for the 
ˇgoverning type definitionˇ as defined in Element Default Valid 
(Immediate) (§3.3.6.2).
5.1.2 The element information item with D.{value constraint}.{lexical 
form} used as its ˇnormalized valueˇ is locally ˇvalidˇ with respect to 
the ˇgoverning type definitionˇ as defined by Element Locally Valid 
(Type) (§3.3.4.4).

and Schema Information Set Contribution: Element Validated by Type, 
[schema normalized value] and [schema actual value], in particular:

1.1 If clause 5.1 of Element Locally Valid (Element) (§3.3.4.3) above 
has applied, then (the [schema normalized value] is) the {lexical form} 
of the {value constraint}

The net effect of these rules is that the [schema actual value] of the 
element is taken from the default value given in the schema if and only 
if the element is empty (has no children). You seem to have convinced 
yourself that a different rule applies, something like

"the [schema actual value] of the element is taken from the default 
value given in the schema if and only if the supplied value is invalid"

but there is no basis for that in the specification.

Michael Kay
Saxonica


On 24/08/2012 00:51, Costello, Roger L. wrote:
>
> Hello Michael,
>
> I am confused. The Title element is declared to be of type string, so 
> a valid value of Title is a string of length zero, right? According to 
> SAXON, that is the case.
>
> /Roger
>
> Answer: the value of Title is the empty string, not the default value.
>
> The reason is that the empty string is a valid value of the string data
>
> type. If you want Title to have the default value then you must
>
> explicitly enter the default value: <Title>Hello World</Title>
>
> WRONG. The default applies when the element is empty, not when it is
>
> invalid.
>
> Michael Kay
>
> Saxonica
>
Received on Friday, 24 August 2012 08:08:10 GMT

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