Question

I have xml files:

<Parent>
  <Child1 ... />
  <Child2 ... />
  ...
  <Child1 ... />
  <Child1 ... />
<Parent>

Where Clild1 and Child2 – childrens of Parent abstract class.

That is, the question was:
How to set a validation scheme for the collection that can have any number of elements different types?

Best regards!

Answer 1

<xs:element name="Parent">
  <xsl:complexType>
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="Child1"/>
      <xs:element name="Child2"/>
    </xs:choice>
  </xs:complexType>
</xs:element>

To illustrate how this works let’s use a simplified version of your example input.

<Parent>
  <Child1 ... />
  <Child2 ... />
  <Child1 ... />
  <Child1 ... />
</Parent>

1. The validator looks at the first element.<Parent> is the first element so validates.
2. The validator then looks for the complex type inside of parent. It finds <Child1>. Since <Child1> is the first element in the choice block it validates.
3. The validator then looks for the <Child2> element. Since <Child2> is next it also validates.
4. The validator then looks at the next element. It is not </Parent> so the validator checks it against the choice block since it can occur an unlimited number of times as maxOccurs=unbounded.
5. The validator finds a <Child1> element which validates.
6. The validator looks for a <Child2> element which doesn’t exist so it finishes the choice block.
7. The validator then looks at the next element. It is not </Parent> so the validator checks it against the choice block since it can occur an unlimited number of times as maxOccurs=unbounded.
8. The validator finds a <Child1> element which validates.
9. The validator then looks at the next element. It is </Parent> which validates.
10. The validator is done. The document validates successfully.

Since minOccurs=0 this also allows for the case where there is 0 occurrences of a <Child1> or <Child2> element. XML schema elements inherit the properties of their parent elements unless explicitly declared. In this case, since we did not declare a minOccurs property for either <Child1> or <Child2> this is the equivalent of <xs:element minOccurs="0" name="Child1"/> and <xs:element minOccurs="0" name="Child2"/>.