Oracle SYS and SYSTEM schemas Don Burleson

From Jeff Hunter we see an excellent summary of the SYS and SYSTEM schemas:

http://www.idevelopment.info/data/Oracle/DBA_tips/Database_Administration/DBA_26.shtml

SYS

All of the base tables and views for the database's data dictionary are stored in the schema SYS. These base tables and views are critical for the operation of Oracle. To maintain the integrity of the data dictionary, tables in the SYS schema are manipulated only by Oracle; they should never be modified by any user or database administrator, and no one should create any tables in the schema of the user SYS. The DBA should change the password for SYS immediately after database creation!!!

SYSTEM

The SYSTEM username creates additional tables and views that display administrative information, and internal tables and views used by Oracle tools. Never create in the SYSTEM schema tables of interest to individual users.
SYSTEM is a little bit "weaker" user than SYS, for example, it has no access to so called X$ tables (the very internal structure tables of Oracle).

Although in real life you may be in a situation when some product or whatever you want to create objects in above mentioned user's schemas. Be flexible, don't sacriface a product only because it will create some objects in SYS or SYSTEM schema

The DBA should change the password for SYSTEM immediately after database creation!!!