Question: how to reinstall xdb in 11g?
Answer: 11.2 – XDB Removal and Reinstall. XDB Removal. The catnoqm. sql script drops XDB. SQL> spool xdb_removal.log. ... 
XDB Installation. The catqm.sql script requires the following parameters be passed to it when run: A. XDB user password. ... 
Verify XDB Installation. SQL> spool xdb_status.txt. SQL> set echo on; SQL> connect / as sysdba.