Question

The following post asks how to indicate that an element is the root element in
an XML schema:

Is it possible to define a root element in an XML Document using Schema?

I have followed the w3schools tutorial on XML Schema but something is still not clear.
Consider example schema 2 from https://www.w3schools.com/xml/schema_example.asp
(reproduced below for convenience). How does this code indicate that <shiporder>
is the root element? Isn’t the example saying that all elements
are valid as root elements?

—————— instance ———————————-

<?xml version="1.0" encoding="ISO-8859-1"?>

<shiporder orderid="889923"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="shiporder.xsd">
  <orderperson>John Smith</orderperson>
  <shipto>
    <name>Ola Nordmann</name>
    <address>Langgt 23</address>
    <city>4000 Stavanger</city>
    <country>Norway</country>
  </shipto>
  <item>
    <title>Empire Burlesque</title>
    <note>Special Edition</note>
    <quantity>1</quantity>
    <price>10.90</price>
  </item>
  <item>
    <title>Hide your heart</title>
    <quantity>1</xample saying that all elements are valid as root elements?quantity>
    <price>9.90</price>
  </item>
</shiporder> 

———————– schema ————————

<?xml version="1.0" encoding="ISO-8859-1" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<!-- definition of simple elements -->
<xs:element name="orderperson" type="xs:string"/>
<xs:element name="name" type="xs:string"/>
<xs:element name="address" type="xs:string"/>
<xs:element name="city" type="xs:string"/>
<xs:element name="country" type="xs:string"/>
<xs:element name="title" type="xs:string"/>
<xs:element name="note" type="xs:string"/>
<xs:element name="quantity" type="xs:positiveInteger"/>
<xs:element name="price" type="xs:decimal"/>

<!-- definition of attributes -->
<xs:attribute name="orderid" type="xs:string"/>

<!-- definition of complex elements -->
<xs:element name="shipto">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="name"/>
      <xs:element ref="address"/>
      <xs:element ref="city"/>
      <xs:element ref="country"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

<xs:element name="item">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="title"/>
      <xs:element ref="note" minOccurs="0"/>
      <xs:element ref="quantity"/>
      <xs:element ref="price"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

<xs:element name="shiporder">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="orderperson"/>
      <xs:element ref="shipto"/>
      <xs:element ref="item" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute ref="orderid" use="required"/>
  </xs:complexType>
</xs:element>

</xs:schema>

---

From my point of view an XML Schema should do two things:

1. define what can occur inside each node
2. define where each node can be placed

And it seems the example fails at #2.
Any Suggestions?

Answer 1

As far as I know, any globally defined element can be used as root element, and XML Schema does not have a notion for specifying what the root element is supposed to be.

You can however work around this by designing your XML Schema well, so that there is only one globally defined element – then only this element is valid as root element.

An example of this can be found at W3Schools (heading Using Named Types)
This example only has one globally defined element, and thus only one possible root element.