Abby has created custom statues made out of scrap metal for over ten years. Abby has kept detailed records of every statue she has ever created. For every sale, she obtains the customer's name and address, and a description of the statue. Ready to take her business to the next level, Abby has hired you to construct an accounting information system, which she wants modeled after her paper records. As you look over her records, you notice that some customer last names have different first names in different records. For example, R. Framington Farnsworth, Bob Farnsworth, and Sam Farnsworth all seem to be the same person. You explain to Abby that every customer must be identified by a unique customer number in the AIS. You are referring to the _____