How to index and query STL map containers by multiple keys?

Question

I came across one requirement where the record is stored as

Name :  Employee_Id  :  Address

where Name and Employee_Id are supposed to be k

Answer 1

If EmployeeID is the unique identifier, why use other keys? I would use EmployeeID as the internal key everywhere, and have other mappings from external/human readable IDs (such as Name) to it.