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Keyref relationships in multi-file schemas

From: BANBURY David <David_BANBURY@rta.nsw.gov.au>
Date: Mon, 11 Feb 2008 19:11:30 +1100
To: xmlschema-dev@w3.org
Message-id: <CF95E76B4CDAA343A2F43638906536AE08FA10E8@REDFX301.corp.rta.nsw.gov.au>

[Newbie posting; I apologise in advance for any poor etiquette]

Before looking at the multi-file scenario, below is a sample XML Schema
describing the nested element structure. The key aspects of the schema
are:
 - The "Superset" root element contains 2 "Subsets".
 - The Subsets contain "Elements" which have attributes.
 - One Subset contains a key definition for its Element.
 - The Superset element contains a keyref relating the Elements from one
Subset to the Elements in the other.

Listing of SingleSchema.xsd:
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://a.b.c" xmlns="http://a.b.c">
	<xsd:element name="Superset">
	    <xsd:complexType>
	        <xsd:sequence>
			    <xsd:element name="Subset1">
			        <xsd:complexType>
			            <xsd:sequence>
			                <xsd:element name="Element1"
minOccurs="0" maxOccurs="unbounded">
			                    <xsd:complexType>
			                        <xsd:attribute
name="PKField" use="required"/>
			                        <xsd:attribute
name="FKField"/>
			                    </xsd:complexType>
			                </xsd:element>
			            </xsd:sequence>
			        </xsd:complexType>
			        <xsd:key name="key_Subset1Element1">
			            <xsd:selector xpath="./Element1"/>
			            <xsd:field xpath="@PKField"/>
			        </xsd:key>
			    </xsd:element>
			    <xsd:element name="Subset2">
			        <xsd:complexType>
			            <xsd:sequence>
			                <xsd:element name="Element1"
minOccurs="0" maxOccurs="unbounded">
			                    <xsd:complexType>
			                        <xsd:attribute
name="PKField" use="required"/>
			                        <xsd:attribute
name="FKField"/>
			                    </xsd:complexType>
			                </xsd:element>
			            </xsd:sequence>
			        </xsd:complexType>
			    </xsd:element>	        </xsd:sequence>
	    </xsd:complexType>
	    <xsd:keyref name="keyref_Superset_Sub2Elem1_Sub1Elem1"
refer="key_Subset1Element1">
	        <xsd:selector xpath="Subset2/Element1"/>
	        <xsd:field xpath="@FKField"/>
	    </xsd:keyref>
	</xsd:element>
</xsd:schema> 


A corresponding data file might look like this:

<?xml version="1.0"?>
<ns:Superset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://a.b.c SingleSchema.xsd"
xmlns:ns="http://a.b.c">
    <Subset1>
        <Element1 PKField="111" FKField="-"/>
        <Element1 PKField="112" FKField="-"/>
        <Element1 PKField="113" FKField="-"/>
    </Subset1>
    <Subset2>
        <Element1 PKField="211" FKField="111"/>
        <Element1 PKField="212" FKField="112"/>
        <Element1 PKField="213" FKField="113"/>
    </Subset2>
</ns:Superset>
 

I appreciate the issues related to the differing scope of the key and
keyref but (in the terms of Bug 4076) the scope of the keyref is wider
than the scope of the key so I believe this is valid. Microsoft's .NET
Parser and MSXML seem to disagree but Xalan, XSV and Saxonica approve.

The problem arises when we split the schema placing the Subset
definitions into separate files. The Subset schemas are then included
into a Superset XSD file and accessed using "ref" as shown in the 3
listings below.

Listing of MultiSchemaSubset1.xsd:
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://a.b.c" xmlns="http://a.b.c">
	<xsd:include schemaLocation="./MultiSchemaSubset1.xsd"/>
	<xsd:include schemaLocation="./MultiSchemaSubset2.xsd"/>
	<xsd:element name="Superset">
	    <xsd:complexType>
	        <xsd:sequence>
	            <xsd:element ref="Subset1" minOccurs="0"/>
	            <xsd:element ref="Subset2" minOccurs="0"/>
	        </xsd:sequence>
	    </xsd:complexType>
	    <xsd:keyref name="keyref_Superset_Sub2Elem1_Sub1Elem1"
refer="key_Subset1Element1">
	        <xsd:selector xpath="Subset2/Element1"/>
	        <xsd:field xpath="@FKField"/>
	    </xsd:keyref>
	</xsd:element>
</xsd:schema>
 
Listing of MultiSchemaSubset2.xsd:
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://a.b.c" xmlns="http://a.b.c">
    <xsd:element name="Subset2">
        <xsd:complexType>
            <xsd:sequence>
                <xsd:element name="Element1" minOccurs="0"
maxOccurs="unbounded">
                    <xsd:complexType>
                        <xsd:attribute name="PKField" use="required"/>
                        <xsd:attribute name="FKField"/>
                    </xsd:complexType>
                </xsd:element>
            </xsd:sequence>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

Listing of MultiSchema.xsd:
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://a.b.c" xmlns="http://a.b.c">
	<xsd:include schemaLocation="./MultiSchemaSubset1.xsd"/>
	<xsd:include schemaLocation="./MultiSchemaSubset2.xsd"/>
	<xsd:element name="Superset">
	    <xsd:complexType>
	        <xsd:sequence>
	            <xsd:element ref="Subset1" minOccurs="0"/>
	            <xsd:element ref="Subset2" minOccurs="0"/>
	        </xsd:sequence>
	    </xsd:complexType>
	    <xsd:keyref name="keyref_Superset_Sub2Elem1_Sub1Elem1"
refer="key_Subset1Element1">
	        <xsd:selector xpath="Subset2/Element1"/>
	        <xsd:field xpath="@FKField"/>
	    </xsd:keyref>
	</xsd:element>
</xsd:schema>


I expected the data file to remain the same (except for the
xsi:schemaLocation) but in order to validate it was now necessary to add
namespace prefixes to the Subset1 & Subset2 data elements. I have tried
but been unable to avoid this requirement; any advice gratefully
accepted.

However, the main problem is that the data file now validates even if
the keyref relationship is deliberately broken as shown below:

<?xml version="1.0"?>
<ns:Superset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://a.b.c MultiSchema.xsd"
xmlns:ns="http://a.b.c">
    <ns:Subset1>
        <Element1 PKField="111" FKField="-"/>
        <Element1 PKField="112" FKField="-"/>
        <Element1 PKField="113" FKField="-"/>
    </ns:Subset1>
    <ns:Subset2>
        <Element1 PKField="211" FKField="119"/>
        <Element1 PKField="212" FKField="112"/>
        <Element1 PKField="213" FKField="113"/>
    </ns:Subset2>
</ns:Superset>


This behaviour is reproduced by Xalan, XSV and Saxonica which leads me
to fear it is my XSD at fault but I can't see the mistake. Again, any
advice gratefully accepted.

Regards,
David Banbury
 
Traffic Systems Branch
Roads & Traffic Authority of NSW

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Received on Monday, 11 February 2008 17:29:18 GMT

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