Access to timely and comprehensive database-related historic data is essential for many DBA activities. The OEM repository not only stores the data for dozens of pre-defined metrics, but also allows easy expansion and customization with User Defined Metrics (UDM). Customization of retention and collection parameters provides the flexibility to address a wide array of DBA problems. Since the OEM repository resides on Oracle, the full power of SQL and PL/SQL as well as all built-in SQL and PL/SQL functions and packages can be used. Furthermore, even greater customization and flexibility can be achieved by creating data structures and packages (in a separate DB user/tablespace). This presentation emphasizes reliance on mathematical verification for DBA “theories.” It includes examples of ad-hoc issues that can be solved effectively with direct access to OEM repository structures. The presentation also covers a more complex enterprise-wide Oracle tablespace size forecasting utility.