Oracle 12.2 introduces the concept of application containers, which act like a mini-root container. They can be used to centralize shared configuration and applications, which are used by their dependent application PDBs.
Create the Application Root
SQL> create pluggable database myapp_root as application container admin user rob identified by rob roles = (DBA); Pluggable database created. SQL> alter pluggable database myapp_root open; Pluggable database altered. SQL> alter pluggable database myapp_root save state; Pluggable database altered.