students.xsd

<?xml version='1.0' encoding='utf-8'?>
<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema'>

  <xs:element name='students'>
    <xs:complexType>
      <xs:sequence>
        <xs:element name='student' type='student_type' minOccurs='0' maxOccurs='unbounded' />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:complexType name='student_type'>
    <xs:sequence>
      <xs:element name='first_name' type='xs:string' />
      <xs:element name='last_name' type='xs:string' />
      <xs:element name='nickname' type='xs:string' />
      <xs:element name='date_of_birth' type='xs:date' />
      <xs:element name='mark' type='xs:positiveInteger' />
    </xs:sequence>
    <xs:attribute name='id' type='xs:positiveInteger' use='required' />
  </xs:complexType>

</xs:schema>