Require XML element in XSD when another element has certain value?

Question

I need a required attribute or element only if a specific value of an enumeration is chosen. Example below:

  <xs:element name="TYPE" type="TestEnum" />
   <!-- // This Element should only required when TYPE = INTERNATIONAL -->
   <xs:element name="IBAN"/>

 </xs:complexType>
<xs:simpleType name="TestEnum">
    <xs:restriction base="xs:string">
        <xs:enumeration  value="NATIONAL"/>
        <xs:enumeration value="INTERNATIONAL"/>
    </xs:restriction>
</xs:simpleType>

Answer 1

XSD 1.1

Here's how use xs:assert to make IBAN be mandatory when TYPE = 'INTERNATIONAL':

<?xml version="1.0" encoding="UTF-8"?>
<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="root">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="TYPE" type="TestEnum" />
        <!-- // This Element should only required when TYPE = INTERNATIONAL -->
        <xs:element name="IBAN" minOccurs="0"/>        
      </xs:sequence>
      <xs:assert test="not(TYPE = 'INTERNATIONAL') or IBAN"/>
    </xs:complexType>
  </xs:element>

  <xs:simpleType name="TestEnum">
    <xs:restriction base="xs:string">
      <xs:enumeration  value="NATIONAL"/>
      <xs:enumeration value="INTERNATIONAL"/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>