How to visualize the relationship of tables in an Oracle database

Oracle SQL Developer Data Modeler - Tool recently launched by Oracle.

Schemaspy is good if you require an offline easy to navigate html report.

Oracle don't provide a tool for free. Their SQL Developer Modeler is pretty good but price-y if you need to buy a commercial license.

If you are interested in platform independence then Power Architect is FOSS.

Download Oracle Data Access Components (ODAC), which is usually packaged with Oracle Developer Tools for Visual Studio. Follow the install instructions for the Oracle ODBC driver. Add a System DSN (Start > Run > type odbcad32 press ENTER).

No you can open an entity-relationship diagram through MS Access, MS Visio, Visual Studio, Enterprise Architect, or other ODBC-compliant data tools.

For example, in MS Access: File > Open > Under "Files of type", select ODBC Databases. This selection is at the bottom of the drop-down list. Select "Database Tools" tab, then "Relationships" to view the Oracle table relationships. Here is a link to an article where Oracle provides documentation on how to visualize the relationships during a migration from Access.

In MS Visio, choose FILE > NEW > "Software and Database" > "Database Model Diagram". Then select "Database" from the top menu, and "Reverse Engineer". Select the ODBC connection. If you get an error, hit escape. Continue until the diagram is loaded.

Enterprise Architect and Visual Studio offer much better capabilities, having similar instructions.

Hope that is clear and helpful. Merry Christmas!