Determinization in case of ambiguity or Should XML validators report on schemas that violate the UPA constraint?

Hello,

 

In the following example schema the element <b/> can appear either as
part of a sequence model group or as part of a choice model group or as
an all model group.

This means that the instance does not follow the Unique Particle
Attribution Constraint (see: "Section 3.8.6: Constraints on Model Group
Schema Components " and Appendix H in "XML Schema Part 1: Structures
Second Edition, W3C Proposed Edited Recommendation").

 

<?xml version="1.0" encoding="UTF-8"?>

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

            <xsd:element name="a">

                        <xsd:complexType>

                                    <xsd:sequence minOccurs="0"
maxOccurs="2">

                                                <xsd:sequence
minOccurs="0" maxOccurs="2">

                                                            <xsd:element
ref="b" minOccurs="0" maxOccurs="2"/>

                                                            <xsd:element
ref="c" minOccurs="0" maxOccurs="2"/>

                                                </xsd:sequence>

                                                <xsd:choice
minOccurs="0" maxOccurs="2">

                                                            <xsd:element
ref="b" minOccurs="0" maxOccurs="2"/>

                                                            <xsd:element
ref="d" minOccurs="0" maxOccurs="2"/>

                                                </xsd:choice>

                                                <xsd:all minOccurs="0"
maxOccurs="1">

                                                            <xsd:element
ref="e" minOccurs="0" maxOccurs="2"/>

                                                            <xsd:element
ref="b" minOccurs="0" maxOccurs="2"/>

                                                </xsd:all>


                                    </xsd:sequence>

                        </xsd:complexType>

            </xsd:element>

            <xsd:element name="b">

                        <xsd:complexType/>

            </xsd:element>

            <xsd:element name="c">

                        <xsd:complexType/>

            </xsd:element>

            <xsd:element name="d">

                        <xsd:complexType/>

            </xsd:element>

            <xsd:element name="e">

                        <xsd:complexType/>

            </xsd:element>

</xsd:schema>

 

 

My question is: should the following example be valid against the schema
or not valid?

 

<a>

   <b/><c/><b/>

</a>

 

 

I see that different XML validators behave differently on this example.
However, I did not see them report an error in the schema.

 

Now, please consider the following schema:

 

<?xml version="1.0" encoding="UTF-8"?>

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

            <xsd:element name="a">

                        <xsd:complexType>

                                    <xsd:sequence>

                                                <xsd:sequence
minOccurs="0">

                                                            <xsd:element
name="b">

 
<xsd:complexType/>

 
</xsd:element>

                                                </xsd:sequence>

                                    </xsd:sequence>

                        </xsd:complexType>

            </xsd:element>

</xsd:schema>  

 

Instance:

 

<a/>

 

Is it valid?

 

 

See, the element b might not appear and that's OK if you ask the inner
sequence but the outer sequence needs to "happen" once (the
minOccurs="1" is implied).

 

So, how should I read this? Is the above single <a/> element instance
valid or not with this schema? Is such a schema legal or not? If the
schema is not legal, must a schema processor report an error?

 

Thanks.

 

Shlomo.