<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="ref"
    targetNamespace="http://ufcpp.net/study/document"
    elementFormDefault="qualified"
    xmlns="http://ufcpp.net/study/document"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
>

  <!-- link, ref -->
  <xs:element name="link">
    <xs:complexType>
      <xs:attribute name="area" type="xs:string" />
      <xs:attribute name="doc" type="xs:string" use="required" />
    </xs:complexType>
  </xs:element>

  <xs:element name="ref">
    <xs:complexType>
      <xs:attribute name="area" type="xs:string" />
      <xs:attribute name="doc" type="xs:string" use="required" />
      <xs:attribute name="id" type="xs:string" use="required" />
    </xs:complexType>
  </xs:element>

</xs:schema>