EX_XML_ID_REF_ENTITY_Clientes.TXT

 <!ELEMENT clientes (cliente+)>
        <!ELEMENT cliente (empresa, rep_clie, limite_credito)>
                <!ATTLIST cliente num_clie ID #REQUIRED>
            <!ELEMENT empresa (#PCDATA)>
            <!ELEMENT rep_clie EMPTY>
                <!ATTLIST rep_clie idven IDREF #REQUIRED>
            <!ELEMENT limite_credito (#PCDATA)>