[xml] Why is this schema valid?

["Yong Chen (yongche)" <chen cisco com>]

Hi,

I have a schema (see at the end of email), I thought it was invalid,
since the "Naming" element in "group1" has the same name as the "Naming"
element in "group2", causing the content of element "Hello" to be
non-deterministic.

But I can create schema context without problem (no errors when calling
xmlSchemaNewParserCtxt, xmlSchemaSetParserErrors and xmlSchemaParse), I
can also validate the xml instance based on this schema and the instance
is OK. I'm using libxml2.6.20.

If I change the "minOccurs" from "1" to "0" for "group1", then I get
error when loading the schema as following:
          ./x.xsd:5: element complexType: Schemas parser error : local
complex type: The content model is not determinist.

But if instead, I only change the "minOccurs" from "1" to "0" for
"group2", then I don't get any error, schema seems to be fine.

Can someone tell me why this schema is valid?

Thanks,
Yong Chen



Schema file 
========================================================================
========================

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema";
elementFormDefault="qualified">
 

  <xs:element name="Hello">
    <xs:complexType>
      <xs:sequence>
        <xs:group ref="group1" minOccurs="1" maxOccurs="1"/>
        <xs:group ref="group2" minOccurs="1" maxOccurs="1"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
 

  <xs:group name="group1">
    <xs:sequence>
      <xs:element name="Naming">
        <xs:complexType>
          <xs:choice>
            <xs:element name="g1_e1" type="xs:string"/>
            <xs:element name="g1_e2" type="xs:string"/>
          </xs:choice>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:group>
 

  <xs:group name="group2">
    <xs:sequence>
      <xs:element name="Naming">
        <xs:complexType>
          <xs:choice>
            <xs:element name="g2_e1" type="xs:string"/>
            <xs:element name="g2_e2" type="xs:string"/>
          </xs:choice>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:group>
 

</xs:schema>

=================End of Schema file
=======================================================





=================XML instance based on the schema
file=======================================

<?xml version="1.0"?>
  <Hello xmlns:xs="http://www.w3.org/2001/XMLSchema";>
    <Naming>
      <g1_e1>I'm g1 e1</g1_e1>
    </Naming>
    <Naming>
      <g2_e2>I'm g2 e2</g2_e2>
    </Naming>
  </Hello>
======================End of XML instance
====================================================