How do I make a valid inline XML schema?

Question

I need to author an embedded XML schema, i.e. where the schema is define within the same XML as the data.

I'm trying to understand how to do it correctly, but so far I'm failing to get a simple example to pass validation. Here's what I was trying to use as a trivial example XML with inline schema:
(Note: The XML structure (e.g. root/item) is already out in the wild so I am constrained to not be able to use a namespace on the data elements.)

<?xml version="1.0"?>
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="#mySchema">
  <xs:schema id="mySchema" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="root">
      <xs:complexType>
        <xs:sequence>
          <xs:element name="item" type="xs:string"
                      maxOccurs="unbounded" minOccurs="0"/>
        </xs:sequence>
      </xs:complexType>
   </xs:element>
 </xs:schema>
 <item>String 1</item>
 <item>String 2</item>
 <item>String 3</item>
</root>

But when I run that XML through the w3.org XML Schema Validator, the XML fails validation, with the following error message saying that it wasn't expecting to see <xs:schema> as a child element!

Invalid per cvc-complex-type.1.2.4: element {http://www.w3.org/2001/XMLSchema}:schema not allowed here (1) in element {None}:root, expecting [{None}:item,$]:

Q: Can you show me an example of a simple XML document with inline schema definition that passes validation?

Matutinal

Did you mean restriction? LIke an enumeration. – Mufinella

With respect, I don't believe that inline schemas are supported everywhere. In fact, I believe they're only rarely supported. – Burdensome

I accidentally down voted this question from my smart phone instead of UpVote and Couldn't revise and Votes are locked. How do i reverse my vote? if @Matutinal edits it i can reverse it again? – Mufinella

@PSCoder thanks for working towards reversing that :) I've now made a trivial edit so that that hopefully your vote will be unlocked. – Matutinal

Answer 1

If your root child has an xs:schema element as a child, then the schema needs to allow it to have such a child. The easiest way to allow it would be to use a wildcard:

<xs:sequence>
  <xs:any processContents="skip" namespace="http://www.w3.org/2001/XMLSchema"
          minOccurs="0" maxOccurs="1"/>
  <xs:element name="item" type="xs:string"
          maxOccurs="unbounded" minOccurs="0"/>
</xs:sequence>

Microdont

Thanks @Michael; I tried that too but validation fails because it's non-deterministic ("Invalid: non-deterministic content model for type None: {Wildcard: #any, skip}/{None}:item"). Nevertheless, it feels like a direction that has potential... but I don't know how to make the xsd say "match anything except <item>. Anyone know if that's possible? – Matutinal

(...sort of like the question https://mcmap.net/q/1624338/-how-to-restrict-an-xs-choice-containing-xs-any, which didn't get a solution) – Matutinal

I was mistaken. I almost did the same as @Michael. But the key in you answer (that I overlooked) that made it work is the namespace="http://www.w3.org/2001/XMLSchema". That makes it match only the <xs:... tag. One I include your namespace restriction, it passes validation. Thanks @Michael! – Matutinal