Extending and Adapting Object Types (BOR) 
You can extend an object type to add more object type components not in the standard version. This ensures that productive workflows and tasks remain executable in the same manner with the original object type.
Example
You have to extend an object type if you want to add more events to it, for example.
You cannot change the object types supplied by SAP. If you want to use one of these object types, but would like to make specific extensions or adaptations in certain areas, you proceed as follows:
You create a new object type as a subtype of the object type that you want to extend. For more information, see Creating Subtypes.
The new object type inherits the components and their implementation from the supertype.
You modify and add to this object type. You can redefine existing attributes and methods and create new object type components. For more information, see Maintaining an Object Type Component.
You make this object type into a delegation type of the supertype. For more information, see Defining Delegation Types.