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RE: two elements with the same name but different types

From: Kevin L Cobb <kevin.cobb@emergint.com>
Date: Mon, 20 Mar 2006 08:26:20 -0500
Message-ID: <12E49A6AAC840749A4488CBC5778A30B3910FB@mail.lou.emergint.com>
To: "andrew welch" <andrew.j.welch@gmail.com>, <xmlschema-dev@w3.org>

You can't define the 'meta' elment multiple times. You want to define it
once and then describe its variablilty internally. The hard part of this
is that you're trying to define the "content" attribute's data type
based on what is in the "name" attribute. I'm not sure you can define
things this way in a schema. You're basically saying:

	IF 		name attribute is 'fixed_1', 'fixed_2', or
'fixed_3'
	THEN 		content attribute can be variable
	ELSE IF 	name attribute is 'fixed_4'
	THEN 		content attribute is 'fixed_5'
	ELSE		content attribute is 'text/html; charset=utf-8'

Which precludes you from defining what is in the 'content' attribute
withought knowing what is in the name attribute first. I'd be surprised
if schema allowed this. 


-Kevin


-----Original Message-----
From: xmlschema-dev-request@w3.org [mailto:xmlschema-dev-request@w3.org]
On Behalf Of andrew welch
Sent: Monday, March 20, 2006 6:56 AM
To: xmlschema-dev@w3.org
Subject: two elements with the same name but different types


Hi,

I'm trying to model the following in a schema:

<head>
  <title>the title<title>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
  <meta name="fixed_1" content="variable"/>
  <meta name="fixed_2" content="variable"/>
  <meta name="fixed_3" content="variable"/>
  <meta name="fixed_4" content="fixed_5"/> </head>

Here the first <meta> has two fixed value attributes, then the following
three have fixed name attributes (which are all different fixed values)
but any content attributes.  The last meta contains two fixed value
attributes, like the first.

Is this possible to model with XML Schema?  Currently I have:

<xs:element name="head">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="title"/>		
					
      <xs:element name="meta">
        <xs:complexType>
          <xs:attribute name="http-equiv" type="xs:string"
fixed="Content-Type"/>
          <xs:attribute name="content" type="xs:string"
fixed="text/html; charset=utf-8"/>
        </xs:complexType>
      </xs:element>
					
      <xs:element name="meta">
        <xs:complexType>
	  <xs:attribute name="name" type="xs:string" fixed="fixed_1"/>
          <xs:attribute name="content" type="xs:string"/>
        </xs:complexType>
      </xs:element>
					
      <xs:element name="meta">
        <xs:complexType>
          <xs:attribute name="name" type="xs:string" fixed="fixed_2"/>
          <xs:attribute name="content" type="xs:string"/>
	</xs:complexType>
      </xs:element>

....
      <xs:element name="meta">
        <xs:complexType>
          <xs:attribute name="name" type="xs:string" fixed="fixed_4"/>
          <xs:attribute name="content" type="xs:string"
fixed="fixed_5"/>
	</xs:complexType>
      </xs:element>

I read that this is ok as long as the element definitions are local and
not global, but I still get the error:

"two elements with the same name <meta> but different types appear in
the content model"

The other problem is defining when "fixed_4" is the value for the name
attribute, "fixed_5" must be the value for the content attribute. 
Isn't this a co-occurrence constraint?  In which case it's not possible
to do this in XML Schema...?

I'm writing this schema within an <xsl:import-schema> element in XSLT
2.0, so it's not possible to use Relax NG here.  This is to validate the
output as it's being generated by the transform... the alternative is to
do the validation as a seperate step in the pipeline, which might be the
only option....

thanks
andrew
Received on Monday, 20 March 2006 13:26:28 GMT

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