Lets start with a photo:
At the moment my focus is Customer Data Integration.
I am married with Simone Visser and father of three daughters. There they are:
The most important property of a unique identification number is that it always refers to just one person. If I have the number than I am able to find the person.
A good illustration is a hospital information system (a HIS). Each patient is assigned a patient identification number.
This is used to couple an operation (or a medical procedure) to the patient.
But what if a patient is in a very severe (and maybe life threatening) situation and is brought to the intensive care unit.