Alias disappearing in oracle 11g whereas it worked fine in 10.2.0.4

Question

sql@10g>select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for IBM/AIX RISC System/6000: Version 10.2.0.4.0 - Productio
NLSRTL Version 10.2.0.4.0 - Production
5 rows selected.
sql@10g>select xmlelement("a", (select xmlelement("c", dummy) from dual) as "b").getStringVal() xml from dual;
XML
<a><b><c>X</c></b></a>
1 row selected.
sql@10g>connect
Connected.
sql@11g>select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for IBM/AIX RISC System/6000: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
5 rows selected.
sql@11g>select xmlelement("a", (select xmlelement("c", dummy) from dual) as "b").getStringVal() xml from dual;
XML
<a><c>X</c></a>
1 row selected.

Answer 1

I'm working with the original poster on this issue. The question here is the difference in alias behavior - don't be distracted by the scalar inline query here. The real-world example has a 0-many result in that inline view. See how the <objects> node gets lost in 11g, but also how the explicit xmlelement reference results in the <objects> node appearing whether or not the inline view returns any rows.
The alias behavior in 10g allowed the results to always validate against the XSD. The use of xmlelement fails XSD validation when there are no rows returned from the inline view as <objects> requires at least one <object> subnode.
11g>select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
10g>select xmlelement("topElement",
  2           (select xmlagg(
  3                     xmlelement("object",
  4                       xmlattributes(object_id as "objectId", object_type as "object_type")))
  5              from all_objects
  6             where object_name = 'DUAL') as "objects").getStringVal() xml
  7    from dual;
XML
<topElement><objects><object objectId="258" object_type="TABLE"></object><obje
ct objectId="259" object_type="SYNONYM"></object></objects></topElement>
1 row selected.
** NOTE: The <objects> element is included in 10g
Now in 11g:
11g>select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
sql>select xmlelement("topElement",
  2           (select xmlagg(
  3                     xmlelement("object",
  4                       xmlattributes(object_id as "objectId", object_type as "object_type")))
  5              from all_objects
  6             where object_name = 'DUAL') as "objects").getStringVal() xml
  7    from dual;
XML
<topElement><object objectId="258" object_type="TABLE"></object><object object
Id="259" object_type="SYNONYM"></object></topElement>
1 row selected.
** NOTE: See above how the <objects> element has been lost in 11g
OK, now we try to replace the "objects" alias with an explicit element:
11g>select xmlelement("topElement",
  2           xmlelement("objects", (select xmlagg(
  3                     xmlelement("object",
  4                       xmlattributes(object_id as "objectId", object_type as "object_type")))
  5              from all_objects
  6             where object_name = 'DUAL')) as "objects").getStringVal() xml
  7    from dual;
XML
<topElement><objects><object objectId="258" object_type="TABLE"></object><obje
ct objectId="259" object_type="SYNONYM"></object></objects></topElement>
1 row selected.
NOTE: This worked as long as the inline view returns a result
11g>select xmlelement("topElement",
  2           xmlelement("objects", (select xmlagg(
  3                     xmlelement("object",
  4                       xmlattributes(object_id as "objectId", object_type as "object_type")))
  5              from all_objects
  6             where object_name = 'XDUAL')) as "objects").getStringVal() xml
  7    from dual;
XML
<topElement><objects></objects></topElement>
1 row selected.
NOTE: The inline view has been changed such that no result is returned.
Now the <objects> element is returned even though there is no lower-level data - a violation of our XSD schema.