Question

I’m trying to write an XSD schema in which some elements can appear in any order – but there can be no duplicates.

So this is valid:

<parent>
    <my-element-A>1</my-element-A>
    <my-element-B>2</my-element-B>
    <my-element-C>3</my-element-C>
</parent>

… and this is valid:

<parent>
    <my-element-B>2</my-element-B>
    <my-element-A>1</my-element-A>
    <my-element-C>3</my-element-C>
</parent>

But this is not:

<parent>
    <my-element-A>1</my-element-A>
    <my-element-B>2</my-element-B>
    <my-element-A>1</my-element-A><!-- Fail! Duplicate my-element-A -->
    <my-element-C>3</my-element-C>
</parent>

How can I do this with XSD?

Answer 1

The <xs:all> element defines “A grouping of a sequence is a set of sub-sequences, some or all of which may be empty, such that each member of the original sequence appears once and only once in one of the sub-sequences and all members of all sub-sequences are in the original sequence.”

  <?xml version="1.0" encoding="UTF-8"?>
  <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
    <xs:element name="parent">
      <xs:complexType>
        <xs:all minOccurs="0">
          <xs:element name="my-element-A" type="xs:string"/>
          <xs:element name="my-element-B" type="xs:string"/>
          <xs:element name="my-element-C" type="xs:string"/>
        </xs:all>
      </xs:complexType>
    </xs:element>
  </xs:schema>