Consulta SQL múltiple SELECT con función xmlagg:los datos no se extraen de la manera requerida

Parece que quieres GROUP BY name en lugar de GROUP BY name, dep_value

SELECT name,
   Rtrim(Xmlagg (Xmlelement (e, dep_value
                                || ';')).extract  ( '//text()' ), ';'),
   Rtrim(Xmlagg (Xmlelement (e, id_dep
                                || ';')).extract  ( '//text()' ), ';')
FROM   (SELECT emp_name,
           dep.dep_value,
           dep.id_dep
    FROM   emp
           inner join dep
                   ON emp.name = dep.name
    WHERE  id_name IN (SELECT name
                       FROM   altname
                       WHERE  id_emp IN (SELECT id_emp
                                         FROM   cnames
                                         WHERE  emp_lvl LIKE '%GGG%')))
    GROUP  BY name