Configuring Siebel Business Applications > About Tables and Columns > Options to Customize the Data Objects Layer >
Options to Use a Predefined One-to-Many Extension Table
More than 20 predefined tables exist that contain a one-to-many relationship with a base table. These tables include the _XM suffix. They include generic columns that you can use to store more data. They allow you to track entities that do not exist in a predefined Siebel application and include a one-to-many relationship to a predefined base table. Because the extension tables themselves are already part of the data objects layer, you are not required to modify the database schema. For more information, see How an Extension Table Stores Custom Data.