Defining company codes
I am doing my first project in SAP-HCM. I have a query regarding company codes. Our customer has a group of companies (say, C1, C2, C3) under the umbrella XYZ froup of companies. I am clear that since each of C1, C2 & C3 is a separate legal entity they should be treated as a "Company Code" in SAP. But what about XYZ? Should we also treat it as a legal entity & therefore as a company code? Please guide me as I am not sure. If XYZ is not going to figure in as a company code, it may have no impact in SAP-HR (as employees are ultimately going to be attached to one of the individual companies C1 or C2 or C3 and not directly to the group XYZ). But what about the impact in SAP-FICO? How are the accounts of companies C1, C2 & C3 going to be consolidated to arrive at the performance of the group XYZ?
I learnt that Company Codes are defined in Financial Accounting. Does it mean that if SAP-FICO is already implemented (or undergoing implementation), then we just have to use those company codes in while implementing SAP-HR?
May be my question is wrongly framed or irrelevant to SAP-HR. If so, please correct me.