(4) Relative object
- Site_admin_1
Field list of relative objects （Parent-Child or Lookup relationships） on the layout are shown.
Fields can be dragged and dropped onto the canvas just as the fields of the main object.
Note that only relative objects that are placed on the canvas already in DataTable elements can have fields added to the layout. Therefore, if no such relative object is on the layout yet, the message shown below will appear.
Once a DataTable component has been added to the layout with a Relative object set,
the relative object list will show a pull-down menu from which you can select the Relative objects on the layout. 
Once a specific Relative object is selected from this pull down menu that objects fields are shown similar to the fields of the main object in the Main Object tab.
The fields shown depend on the logged in user's profile permissions in Salesforce.
Only fields that the user has write access to will be able to shown as Text[Input] fields and only fields the user has read access to will be shown as Text[Output] fields.