Create the Data Dictionary in Oracle

•The data dictionary tables are the first objects created in Oracle database.

•They must be created and resided in SYSTEM tablespace.

•Whenever you create your database using dbca (Database Configuration Assistant) Oracle automatically creates the data dictionary.

•But if you create database manually which is described as in Manually Create an Oracle Database then to build or create data dictionary objects, you must run several scripts, while connecting to database as a user with SYSDBA privileges.

Here a list of scripts that you need to run to build data dictionary objects. You can get and run these scripts from $ORACLE_HOME/rdbms/admin/
1)catalog.sql: Creates the data dictionary and public synonyms for many of its views. It also grants PUBLIC access to the synonyms.

2)catproc.sql: This script builds all data dictionary objects required for PL/SQL.

3)catclust.sql: This script creates Real Application Clusters data dictionary views.

To know the additional scripts just have a look at,
Addiional Data Dictionary Scripts