PS - HR ( time sheet)

hello ppl i am doing a project on time sheet which includes a link between HR and PS....

It would be nice if anyone can explain me how is the master cost center and the sub cost centers are linked???

cost center is created using a TC KS01 right.. is there any way we can link the sbu cost center to the master one???? because in project system we have a cost center for each activity. so at a time a person is assigned to more than one cost center how can this be done????

i dono if this is a relevant question... plz correct me if i am wrong...