Question about attribute inheritence in XML Schemas using <xsd:extension>

[Sean Bright]

Hi there.

I'm having a problem which I hope is a simple one... Any help would be appreciated. I think it has something to do with the way attributes are (or are not) inherited in schemas...

This is the content of my XML Schema (minus the schema tag):

<xsd:complexType name="AType">
<xsd:attribute name="attr1" type="xsd:string" />
<xsd:attribute name="attr2" type="xsd:string" />
</xsd:complexType>

<xsd:complexType name="BType">
<xsd:complexContent>
<xsd:extension base="AType">
<xsd:attribute name="attr3" type="xsd:string" />
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>

<xsd:element name="mydoc">
<xsd:complexType>
<xsd:choice maxOccurs="unbounded">
<xsd:element name="a" type="AType"/>
<xsd:element name="b" type="BType"/>
</xsd:choice>
</xsd:complexType>
</xsd:element>

In my instance document, I simply want to be able to do the following:

<mydoc xmlns="http://foo.org/foo.xsd">
<a attr1="1" attr2="2"/>
<b attr1="1" attr2="2" attr3="3"/>
</mydoc>

Whenever I try to validate the document, however, I get an error that attr1 and attr2 are not valid for <b>. But <b> is of BType which extends AType and attr1 and attr2 are defined for AType. What am I missing?

Thanks in advance,
Sean

 

[C. M. Sperberg-McQueen]

Hi there.

I'm having a problem which I hope is a simple one... Any help would be appreciated. I think it has something to do with the way attributes are (or are not) inherited in schemas...

It may. I suspect it has something to do with the
way namespaces work in XML and in XML Schema.

This is the content of my XML Schema (minus the schema tag):

Can you show us the start-tag of the schema element, too? Only that will allow us to see whether what is happening below is what you think is happening. I need to see your namespace declarations and your targetNamespace attribute.

<xsd:complexType name="AType">
<xsd:attribute name="attr1" type="xsd:string" />
<xsd:attribute name="attr2" type="xsd:string" />
</xsd:complexType>

OK. This declares a complex type named "AType" in the
target namespace.

<xsd:complexType name="BType">
<xsd:complexContent>
<xsd:extension base="AType">
<xsd:attribute name="attr3" type="xsd:string" />
</xsd:extension>
</xsd:complexContent>
</xsd:complexType>

OK. This declares a complex type named "BType" in
the target namespace, which in turn extends a complex
type named "AType" in whatever namespace (if any) is
declared as the default namespace in the schema
document.

The local elements will either be qualified names in the target namespace (if you have one, and if you have specified elementFormDefault as "qualified"), or unqualified names (names not associated with any namespace -- some people like to say 'in the anonymous namespace' and others to say 'not in any namespace') if you have left elementFormDefault as "unqualified" (the default).

When I reconstructed your schema just now, I wrote

<xsd:schema
xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://foo.org/foo.xsd" xmlns="http://foo.org/foo.xsd" elementFormDefault="qualified">

and I get no errors from Xerces J when I validate your
sample document.

In my instance document, I simply want to be able to do the following:

<mydoc xmlns="http://foo.org/foo.xsd">
<a attr1="1" attr2="2"/>
<b attr1="1" attr2="2" attr3="3"/>
</mydoc>

Whenever I try to validate the document, however, I get an error that attr1 and attr2 are not valid for <b>. But <b> is of BType which extends AType and attr1 and attr2 are defined for AType. What am I missing?

It's more helpful if you show the error message. My guess is that one way or another the elements in your document, or the element declarations in your schema, or the type definitions in your schema, did not end up in the same namespace.

I hope this helps.

-C. M. Sperberg-McQueen
World Wide Web Consortium

 

[Sean Bright]

Can you show us the start-tag of the schema element, too? Only that will allow us to see whether what is happening below is what you think is happening. I need to see your namespace declarations and your targetNamespace attribute.

Aye, there's the rub...

You go on to mention elementFormDefault and attributeFormDefault. The problem was that in my <xsd:schema> tag I was specifying that the attributeFormDefault was 'qualified'

Stupid mistake on my part. Combination of my own mistakes and Visual Studio .NET's intellisense functionality. Apparently Intellisense (which uses XML Schema to drive it) can not handle the <xsd:extension> types and I was using the appearance (or lack there of) of attribute options as the error check, as opposed to running the validator each time. That'll teach me too be lazy.

Thanks for your feedback, I thought I was going crazy.

Oh, and my targetNamespace was "http://foo.org/foo.xsd" but ultimately that wasn't the fish I should have been frying.

Thanks,
Sean