Final answer:
When gathering requirements for HR Services, it is best to begin by defining the Service, Topic Category, and COE.
Step-by-step explanation:
When gathering requirements for HR Services, the best approach is to begin by defining the Service and then work upwards, categorizing in progressively more detail. The basic categories used are: HR Service, Topic Category, COE. This means that you start by defining the HR Service, then categorize it by Topic, and finally determine the Center of Expertise (COE) associated with that service.