I was about to go for a run on the beach when my
4-year-old daughter asked, "Daddy, can you bring me back some shells? It's ok if the shell is chipped or missing a
piece but I don't want any shell pieces." Although it was easy for her to distinguish a chipped shell from a shell piece, I had a much more difficult time separating the two while jogging along the beach. Where do we draw the line between a chipped shell and a shell piece? That is, at what point does a shell change so dramatically that it is no longer a shell but now a piece of a shell?  

After returning home completely 'shell-less', I started thinking about how this shell story relates to a challenge we sometimes have to face in capturing requirements. William Kent in "Data and Reality" raises a similar dilemma on replacing parts in a car. If you replace the windshield wipers, it is still the same car. But what if you replace the car engine and car body? Is it then still the same car? In your organization, if a customer moves to a different location is it a new customer? If no, is there anything about a customer that could change (name, tax identifier, or even gender) that could turn an existing customer into a different customer? What about a product or employee or any other concept important to your organization?

Have you ever had to analyze or model a concept in your organization where enough changes could occur to create a completely new concept?  How did you handle it?