How to allow interleaving of unordered elements in XSD?

Question

I have to write a schema where it does not matter the order of nested elements, and there could more nested elements of the same type.

I tried to use xs:all and xs:sequence , but it doesn't work.

This XML should be valid:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="test.xsd">
    <elementB>B</elementB>
    <elementA>A</elementA>
    <elementA>A</elementA>
</test>

and here are the XSDs which I tried:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="test">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="elementA" type="xs:string" 
                            minOccurs="0" maxOccurs="unbounded"/>
                <xs:element name="elementB" type="xs:string" 
                            minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

First XSD schema has problem with ordering.

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"
           vc:minVersion="1.1">
    <xs:element name="test">
        <xs:complexType>
            <xs:all>
                <xs:element name="elementA" type="xs:string" 
                            minOccurs="0" maxOccurs="unbounded"/>
                <xs:element name="elementB" type="xs:string" 
                            minOccurs="0" maxOccurs="unbounded"/>
            </xs:all>
        </xs:complexType>
    </xs:element>
</xs:schema>

The second XSD looks promising but I can't setup Intellij to use it correctly for XML. (I switched ussing of XML Schema 1.1 here File->Settings->Languages & Frameworks->Schemas and DTDs->Default XML Schemas ) My IntelliJ version is 2019.2.3.

Answer 1

Clearly the xs:sequence version of the XSD imposes an ordering.

The xs:all version of the XSD uses xs:all/xs:element[@maxOccurs="unbounded"] , which requires XSD 1.1.

XML Oxygen validates your XML against your xs:all XSD successfully.

IntelliJ has XSD 1.1 support, but perhaps it's incomplete, or perhaps the spec is ambiguous here – no time to investigate that right now.

However, if your actual case is as simple as your posted case, you can use xs:choice to achieve order independence without a dependency on XSD 1.1:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning"
  vc:minVersion="1.0">
  <xs:element name="test">
    <xs:complexType>
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element name="elementA" type="xs:string"/>
        <xs:element name="elementB" type="xs:string"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>
</xs:schema>

Hopefully this will allow you to work-around any IntelliJ issue that may have been blocking you.

Answer 2

Your second schema (the "promising" one) works for me. Tried it in oXygen and it works fine. I don't know how to set up IntelliJ for XSD 1.1 validation, I'm afraid.

If any of the elements in a fixed set (A, B, C...) can appear any number of times then you don't need XSD 1.1: you can write the content model as

<xs:choice minOccurs="0" maxOccurs="unbounded">
  <xs:element name="A">
  <xs:element name="B">
  <xs:element name="C">
</xs:choice>