RKM is the ODI knowledge module used for reverse engineering the model.
Reverse-engineering is the process of creating or updating a model in ODI.
ODI can use JDBC to retrieve metadata. The table and column definitions are those accessible from the JDBC.
You can also read the metadata from application metadata repository. For example, Oracle E-Business Suite stores the table and column description in the Application Object Library (AOL) tables, which are the base to generate the eTRM (Technical reference manuals).
Writing a EBS KM allows us to get the information about the table and column definitions.
RKM allows you to write the custom reverse-engineering logic.