Data Modeler

To reverse engineer a schema:

1. download the beta-version here.
   
2. Select File
   
3. Select Import
   
4. Select DB Catalog
   
5. Click 'Add' on the 'Connect to Database' window, and type in the requested info.
6. Select the schema.
   
7. Select the items you want.

---

To generate the DDL:

1. Select View
   
2. Select DDL File Editor
   
3. Click Ok
   
4. Click Generate
   

A very complete example of reverse engineering by Lewis C

Oracle Users Guide PDF