Following are the uploads or add-ons on this site this week

Codd's 12 rules
Codd's 12 rules for building a complete RDBMS. Codd's Rule in easy laguage can also be found by clicking this link.

Client-Server Architectures

Two Tier Architectures

Three Tier (Multi tier) Architectures

Oracle reference [pdf format]

Two Phase Commit

Executing OS command from PL/SQL
execute OS programs from pl/sql.