Having one element with two different definition/type in XSD 1.0

Question

I have to write an XML schema (in XSD 1.0) to validate a given document.

In this document, there is an element called box that either:

• has two required attributes, name and weight and some other optional one, no content

• has one required attribute, name, no other attributes, and several element as content (including box elements).

For example:

<box name="box_1"> <!-- type 2 -->
    <box name="box_2"> <!-- type 2 -->
        <box name="box_3" weight="10" height="5" /> <!-- type 1 -->
        <box name="box_4" weight="15" /> <!-- type 1 -->
    </box>
    <box name="box_5"> <!-- type 2 -->
        <box name="box_6" weight="21" /> <!-- type 1 -->
    </box>
</box>
<box name="box_7" weight="21" /> <!-- type 1 -->

The issue is that:

• I cannot define box with two different types (xmllint does not recognise which type is used and invalidate any box that doesn't have the attribute weight)

• I cannot add <xs:attributes> in a <xs:choice>

• I cannot use <xs:alternative> because I have to use XSD 1.0

• I cannot make weight optional, it has to be required

• I cannot modify the given xml document

This, for example, does not work:

<xs:complexType name="closet">
    <xs:choice maxOccurs="unbounded">
        <xs:element name="box" type="TboxComplex" />
        <xs:element name="box" type="TboxSimple" />
    </xs:choice>
</xs:complexType>

<xs:complexType name="TboxComplex">
    <xs:choice maxOccurs="unbounded">
            <xs:element name="box" type="TboxComplex" />
            <xs:element name="box" type="TboxSimple" />
    </xs:choice>
    <xs:attribute name="name"   type="xs:string"  use="required" />
</xs:complexType>

<xs:complexType name="TboxSimple">
    <xs:attribute name="name"   type="xs:string"  use="required" />
    <xs:attribute name="weight" type="xs:integer" use="required" />
    <xs:attribute name="height" type="xs:integer" use="optional" />
</xs:complexType>

> xmllint --schema room.xsd room.xml 
room.xml:9: element box: Schemas validity error : Element 'box', attribute 'weight': The attribute 'weight' is not allowed.`
room.xml:9: element box: Schemas validity error : Element 'box', attribute 'height': The attribute 'height' is not allowed.
room.xml:9: element box: Schemas validity error : Element 'box': Missing child element(s). Expected is ( box ).

Could you help me find a way to define that element without needing to change the xml document or switch to XSD 1.1, please? Thank you in advance!

Answer 1

XSD 1.0 is not capable of defining this constraint. You will need to use some other validation technology such as XSD 1.1, RelaxNG, or Schematron; or you might be able to do it with XSD 1.0 if you are prepared to add xsi:type attributes to your XML instance.