In all_objects theres a a column called SUBOBJECT_NAME, and the docs say that this is:
Name of the subobject (for example, partition)
If you do the following query:
select * from all_types where owner = 'MDSYS' and type_name = 'SDO_TGL_OBJECT_ARRAY'
You find that MDSYS.SDO_TGL_OBJECT_ARRAY has a subobject called $VNS_1. What is it? How can types have subobjects?
I noticed the answer you got for this question over at StackOverflow, which I think is accurate. For the record here, the suggestion is that it's to do with type versioning.
I'll expand on that a bit here, hopefully to give a better understanding (and also because researching this was interesting).
Oracle objects aren't versioned, but types are, so my best guess is that Oracle used the subobject name to give a method of versioning the objects associated with the type definitions. This is sort of confirmed if you look at the data dictionary definitions in $ORACLE_HOME/rdbms/admin/catadt.sql, you'll see the %_TYPES views join between sys.type$ and sys.obj$ and have a condition of "o.subname IS NULL" and a comment "only the most recent version".
A quick experiment is interesting:
SQL> CREATE OR REPLACE TYPE ajm_t AS OBJECT(a number, b number);
2 /
SQL> SELECT t.toid,t.version#,t.version,t.tvoid,o.obj#,o.name,o.subname
2 FROM type$ t INNER JOIN obj$ o
3 ON t.tvoid=o.oid$
4 WHERE o.name='AJM_T';
TOID VERSION# VERSION TVOID OBJ#
-------------------------------- ---------- ------------------------------ -------------------------------- ----------
NAME SUBNAME
------------------------------ ------------------------------
7E4C10976F759614E040A8C068385DCF 1 $8.0 7E4C10976F759614E040A8C068385DCF 74708
AJM_T
So, initially we have one type with a version name of "$8.0" (at a guess, referring to being introduced in Oracle 8.0, or the definition scheme introduced then).
SQL> ALTER TYPE ajm_t ADD ATTRIBUTE (c number);
Type altered.
SQL> SELECT t.toid,t.version#,t.version,t.tvoid,o.obj#,o.name,o.subname
2 FROM type$ t INNER JOIN obj$ o
3 ON t.tvoid=o.oid$
4 WHERE o.name='AJM_T';
TOID VERSION# VERSION TVOID OBJ#
-------------------------------- ---------- ------------------------------ -------------------------------- ----------
NAME SUBNAME
------------------------------ ------------------------------
7E4C10976F759614E040A8C068385DCF 1 $8.0 7E4C10976F7A9614E040A8C068385DCF 74708
AJM_T $VSN_1
7E4C10976F759614E040A8C068385DCF 2 $VSN_2 7E4C10976F759614E040A8C068385DCF 74709
AJM_T
SQL> ALTER TYPE ajm_t ADD ATTRIBUTE (d number);
Type altered.
SQL> SELECT t.toid,t.version#,t.version,t.tvoid,o.obj#,o.name,o.subname
2 FROM type$ t INNER JOIN obj$ o
3 ON t.tvoid=o.oid$
4 WHERE o.name='AJM_T';
TOID VERSION# VERSION TVOID OBJ#
-------------------------------- ---------- ------------------------------ -------------------------------- ----------
NAME SUBNAME
------------------------------ ------------------------------
7E4C10976F759614E040A8C068385DCF 1 $8.0 7E4C10976F7A9614E040A8C068385DCF 74708
AJM_T $VSN_1
7E4C10976F759614E040A8C068385DCF 2 $VSN_2 7E4C10976F809614E040A8C068385DCF 74709
AJM_T $VSN_2
7E4C10976F759614E040A8C068385DCF 3 $VSN_3 7E4C10976F759614E040A8C068385DCF 74710
AJM_T
For the first modification, there's a bit of a weird artifact that the VERSION in type$ is "$8.0" but the subobject name given in obj$ is "$VSN_1". After the first version, things start to look more consistent. When a type is modified, a new object with a NULL subobject name is created, a new type is created and the subobject of the old object becomes the version field of the old type.
