sap service throws error 'Method not implemented'

Hi guys,

I recently discovered that the service HCMFAB_TIMESHEET_MAINT_SRV has a lot of methods in the class CL_HCMFAB_TIMESHEET_CR_DPC which are not implemented whereas others are implemented. Hence, the service will throw an error when trying different functionalaties (e.g. if I try to create a TimeEntry via method TIMEENTRIES_CREATE_ENTITIY).

This let me with the following questions:
Is it normal that some methods of a standard service are not implemented?
In case they are not implemented, will then the generic code in the IWBEP interface be used?
How does the methods of a service and the interfaces of IWBEP work together?

Hopefully you can clarify the topic.

Cheers,
Thorsten