It just means that this is a logical not a true partition of the data, eg
SQL> create table t1 ( x int, y int )
2 partition by list ( x )
3 subpartition by list ( y )
4 (
5 partition p1 values (1)
6 (
7 subpartition p1a values (10),
8 subpartition p1b values (20)
9 ),
10 partition p2 values (2)
11 );
Table created.
SQL>
SQL> insert into t1 values (1,10);
1 row created.
SQL> insert into t1 values (1,20);
1 row created.
SQL> insert into t1 values (2,30);
1 row created.
SQL>
SQL> select x,y, dbms_rowid.rowid_object(rowid)
2 from t1;
X Y DBMS_ROWID.ROWID_OBJECT(ROWID)
---------- ---------- ------------------------------
1 10 101001
1 20 101002
2 30 101003
3 rows selected.
SQL>
SQL> select object_id, data_object_id, subobject_name
2 from user_objects
3 where object_name = 'T1';
OBJECT_ID DATA_OBJECT_ID SUBOBJECT_NAME
---------- -------------- --------------------
100998
100999 P1
101000 P2
101001 101001 P1A
101002 101002 P1B
101003 101003 SYS_SUBP5199
6 rows selected.
Notice that the data in the table *only* maps to a data object id. The others just reflect the dictionary definition