XML Schema Validation Failure of Nested Element of Imported Schemas

Question

I have an issue with XML Validation against a nested schema. I believe the issue is due to a misunderstanding of imports, and I think I understand why (explained after sample code). I would like assistance in helping me understand my understanding and recommendations on how to address it.

The current error message I am getting is:

Exception has occurred: XMLSyntaxError
Element '{http://example.com/A.xsd}tNestedElementB': This element is not expected. Expected is ( {http://example.com/B.xsd}tNestedElementB ). (<string>, line 0)

Here is A.xsd where we import B.xsd and then use the tClassB in the a complex type.

<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="A" targetNamespace="http://example.com/A.xsd" elementFormDefault="qualified"
           xmlns="http://example.com/A.xsd"
           xmlns:ans="http://example.com/A.xsd"
           xmlns:bns="http://example.com/B.xsd"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:import namespace="http://example.com/B.xsd" schemaLocation="B.xsd"></xs:import>

    <xs:complexType name="tBasic">
        <xs:choice maxOccurs="unbounded">
            <xs:element name="MyClass" type="bns:tClassB" minOccurs="0" maxOccurs="1"/>
        </xs:choice>
    </xs:complexType>
    <xs:element name="Basic" type="tBasic">
    </xs:element>
</xs:schema>

Here is B.xsd where we have tNestedElementB within the tClassB complex type:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="B" targetNamespace="http://example.com/B.xsd" elementFormDefault="qualified"
           xmlns="http://example.com/B.xsd"
           xmlns:bns="http://example.com/B.xsd"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">

    <xs:complexType name="tClassB">
         <xs:sequence minOccurs="0" maxOccurs="unbounded">
             <xs:element name="tNestedElementB" type="xs:string"></xs:element>
        </xs:sequence>
        <xs:attribute name="Comment" default="Hi" type="xs:string">
         </xs:attribute>
    </xs:complexType>

</xs:schema>

Finally, here is the sample.xml file that

<?xml version="1.0" encoding="utf-8"?>
<Basic xmlns="http://example.com/A.xsd" xmlns:bns="http://example.com/B.xsd">
    <MyClass Comment="DEF">
        <!-- This line gives the error message -->
        <tNestedElementB>DOES_NOT_WORK</tNestedElementB>
        <bns:tNestedElementB>WORKS</bns:tNestedElementB>
    </MyClass>
</Basic>

Based on the fact that adding the bns: to the tNestedElementB usage in sample.xml makes the problem go away indicates to me that the issue is namespace related. Our objective in B.xsd is to have a lot of common types that we want to use, so there are lots of <simpleType> and <complexType> definitions in there. To date, the complexTypes have been mostly for specifying attributes on an object, but we are starting to venture into complexTypes with multiple levels of nesting elements.

I understand that the import does not pollute the namespace of A, and the definition in A.xsd of <xs:element name="MyClass" type="bns:tClassB" minOccurs="0" maxOccurs="1"/> really is just making an element referring to that one complexType in B.

What we'd like to know is this: are there ways that we can avoid the namespace qualification in the root xml - is there a way to transparently map the bns:tNestedElementB in A.xsd such that a client writing xml files can be blissfully ignorant of the need to namespace that one nested item?

---

For completeness, here is the bit of Python code I am using for this (Python 3.7 64-Bit Windows):

from lxml import etree, objectify

xsd = etree.parse('A.xsd')
schema = etree.XMLSchema(xsd)

filepath = "./example.xml"
parser=etree.XMLParser(remove_comments=True, attribute_defaults=True, schema=schema)
tree=objectify.parse(filepath, parser=parser)

Thank you!

Answer 1

I suspect that for your use case you want xs:include rather than xs:import.

If a schema document has a target namespace, then

• Global elements declared in that document must be in that namespace

• Locally declared elements in that document are either in the target namespace (if elementFormDefault="qualified") or in no namespace. They will never be in the namespace of the importing module.

By contrast, xs:include adds declarations to the namespace of the including module.