RE: Question on use="required"

If an attribute is required you cannot specify a value constraint [1]

http://www.w3.org/TR/xmlschema-1/#src-attribute


1 default and fixed must not both be present. 
2 If default and use are both present, use must have the ·actual value·
optional


Anli Shundi                         ashundi@tibco.com
TIBCO Software Inc.                 office: (919) 969-6518
www.tibco.com

-----Original Message-----
From: Stefan Wachter [mailto:Stefan.Wachter@gmx.de]
Sent: Wednesday, August 14, 2002 10:25 AM
To: Jeni Tennison; xmlschema-dev@w3.org
Subject: Re: Question on use="required"



Hi Jeni,

I agree with your answer that in the instance document there must appear a
value for an attribute whose use is required. But I think it would be good
to
allow value constraints for such attributes in the schema for two reasons:

1. If I want to express that an attribute must be present and have a certain
value.

2. There is a great schema which I import and which contains value
constraints for various declarations. Some people (like me) do not like
default values
and want that an instance author must specify all values. Therefore I would
restrict the imported declarations by adding the use="required" attribute.
These declarations would now have value constraints and the use="required"
attribute.


--Stefan

PS:  So there is an error in the Microsoft testcase attribute/attP009.xsd.
Theres is the complexType

	<xsd:complexType name="attRef">
		<xsd:attribute name="att" use="required" fixed="37"/>
	</xsd:complexType>

which is valid. But in the accompanying instance document attP009.xml there
is no value for the attribute.


> Hi Stefan,
> 
> > I have a question regarding attribute declarations whose use
> > attribute has the value "required". Must there be values for such
> > attributes in instance documents or is it also allowed to have a
> > fixed/default values filled in?
> 
> The instance document must specify a value for the attribute [1]. I
> *think* that you're not allowed to specify a default value for a
> required attribute in the schema, because default values only apply
> when the attribute is missing, and if it's required it can't be
> missing, but I can't find the constraint specifying that at the
> moment. You can have fixed values for required attributes, however
> (particularly useful for indicating the version of a markup language).
> 
> Cheers,
> 
> Jeni
> 
> [1] Clause 4 of http://www.w3.org/TR/xmlschema-1/#cvc-complex-type
> 
> ---
> Jeni Tennison
> http://www.jenitennison.com/
>

Received on Wednesday, 14 August 2002 10:40:08 UTC