Customer look-up is expected to be both quick and accurate.

In some systems, frequently the search will use an id-number, which is ideal for quick and accurate retrieval. In other systems identity numbers are just not available or the business does want to make its customer feel like a number or an account.

When an id-number is not available, the search will need to be driven by some other piece of identifying data.

One of the challenges for the system designer is to decide which attribute or attributes are the best to use for this identity search.

Given a choice of name, birth date, telephone numbers or an address, how does one determine the best?

In an ideal world, one would try combinations of each attribute over a period of time and measure the system’s results and the business benefits. In the real world, the decision often has to be made without empirical evidence.

Because dates suffer from the fact that a valid variation in any component creates a completely different but valid date, a search driven by a date is going to fail when one or more of the components are wrong.

Except where property addresses are the foundation of "customer" (for example, electricity and water companies), then addresses suffer from the fact that customers move regularly. A search driven by address is therefore going to fail when an address change has not been notified to the system.

Except when telephone numbers are the foundation of "customer" (e.g. telephone companies or utility and emergency services), then telephone numbers suffer from the fact that customers move and change them, use home, work, mobile and public numbers. A search driven by telephone numbers is therefore going to fail when the number has not previously been notified to the system. And like dates, errors in the number, or variations in format make indexing with such numbers quite unproductive.

Names avoid the pitfalls of dates, phone numbers and addresses. Unlike dates or telephone numbers, if a character in a name is different, then it still has a good chance of being identified because systems can compensate for variation and error in names. And unlike addresses and phone numbers, names tend to remain more stable over time.