How to access parent element in XSD assertion XPath?

Question

I am trying to write an assertion that will make the values of @row and @column less than or equal to the values of @rows and @columns in the parent element <structure>.

<xs:element name="structure">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="cell" maxOccurs="unbounded">
                <xs:complexType>
                    <xs:attribute name="row" type="xs:positiveInteger"/>   
                    <xs:attribute name="column" type="xs:positiveInteger"/>
                    <xs:assert test="@row le @rows"/>
                    <xs:assert test="@column le @columns"/>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
        <xs:attribute name="rows" type="xs:positiveInteger" use="optional"/>
        <xs:attribute name="columns" type="xs:positiveInteger" use="optional"/>
    </xs:complexType>
</xs:element>

Are my assertions in the wrong place? What XPath expression do I use to specify the parent node? My editor isn't letting me write ..@rows.

Answer 1

An assertion XPath cannot reach outside of its context.

So, move your assertion up to the structure element, and use an every ... satisfies assertion test:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"
           elementFormDefault="qualified"
           vc:minVersion="1.1">
    <xs:element name="structure">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="cell" maxOccurs="unbounded">
                    <xs:complexType>
                        <xs:attribute name="row" type="xs:positiveInteger"/>   
                        <xs:attribute name="column" type="xs:positiveInteger"/>
                    </xs:complexType>
                </xs:element>
            </xs:sequence>
            <xs:attribute name="rows" type="xs:positiveInteger" use="optional"/>
            <xs:attribute name="columns" type="xs:positiveInteger" use="optional"/>
            <xs:assert test="every $r in cell/@row satisfies @rows >= $r"/>
            <xs:assert test="every $c in cell/@column satisfies @columns >= $c"/>
        </xs:complexType>
    </xs:element>
</xs:schema>