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Peter, I don't know if this can be done in XSD, but here is a RELAX NG
schema ( compact syntax ) that can handle it:
start = computer_list
computer_list = element computer_list { computer* & computerDefault }
computer = element computer { computerNames }
computerDefault = element computer { attribute default { xsd:boolean },
computerNames }
computerNames = 'HP' | 'Dell'
You can interleave ('&' connector) the single 'computer with default
attribute' with one or more 'computers without default attribute'.
Tom
-----Original Message-----
From: Peter Loh Yoon Chao [mailto:yoonchao@starhub.net.sg]
Sent: Wednesday, April 07, 2004 8:23 AM
To: xml-dev@lists.xml.org
Subject: [xml-dev] XML Schema Question: specifying restrictions for a list
of elements
Hi,
I have the following construct in my XML document:
<computer_list>
<computer default="true">Dell</do_type>
<computer>HP</do_type>
</computer_list>
Only 1 of <computer> can have the "default" attribute set to true. I am
trying to specify the corresponding XML schema to enforce this. I tried the
following among other variations:
<xs:element name="computer_list">
<xs:complexType>
<xs:sequence>
<xs:element maxOccurs="unbounded" name="computer">
<xs:complexType>
<xs:simpleContent>
<xs:restriction base="xs:string">
<xs:enumeration value="Dell"/>
<xs:enumeration value="HP"/>
</xs:restriction>
<xs:extension base="xs:string">
<xs:attribute name="default"
type="xs:boolean" use="optional" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
The above suffers from the following problems:
1.) It allows the "default" attribute to be set to true for any number of
<computer>.
2.) With the <xs:restriction> element, the parser complained that "Element
'extension' is invalid, misplaced, or occurs too often."
Would really appreciate any input as to the modifications required to
achieve my objectives. Thanks.
Peter
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