Here’s a great example from Robert Cringley of why crisp requirements aren’t. At least not in almost any system that’s likely to be useful. I think it’s worth quoting the relevant part at length, there’s some other stuff about Google and mobile phones in the original article. Hands up everyone who’s worked on a system that assumed that a social security number identified a person…
While politicians and the U.S. Census Bureau may disagree on how many illegal aliens are living in the United States, the big credit reporting agencies have a pretty solid handle on the number and it is 17 million. That’s 17 million adults of unproved nationality who have ongoing financial relationships with businesses or — believe it or not — governments. [...] But it isn’t in any way close to the total number of U.S residents who have financial identities not tied to a Social Security number. That would be 37 million, meaning there are 20 million participants in the U.S. gray economy who aren’t illegal, who are legitimate citizens. This means about 10 percent of U.S. residents are financially invisible, or think they are.
There is a lot to be learned if you think about these numbers. [...] The first thing to be noticed is that these supposedly invisible people have been, well, noticed. The credit reporting agencies have a handle on total numbers and have a lot of information on specific individuals. So members of the gray economy are, for the most part, not invisible at all, just difficult to identify as individuals. But thanks to data mining down at the credit bureau, it is getting harder and harder to hide.
A lot of this sleuthing comes down to a surprising artifact, the Social Security number. One would think that surprising for an economic class of people best known for not having Social Security numbers. Ah, but they do have Social Security numbers, just not their own. You need a Social Security number to sign up for utility services, for example. No Social Security number, no electricity, gas, phone, or satellite TV. So what’s a poor alien to do? They go down to some local hangout and BUY a Social Security number to give to the utility. This has to be a legitimate number or it won’t fly with utility computer systems, but does it have to be the customer’s own number? Good question.
Here’s where we have an interesting business ethics issue. Say you are the electric company and someone tries to set up service using a Social Security number that already exists in your database and is clearly borrowed, bought, stolen, or simply made up. What do you do? Most utilities go ahead and set up the account, because to them what counts is whether the new customer will actually pay that bill and it turns out that people operating on such borrowed numbers are more reliable bill payers than the rest of us. They can’t afford to get in trouble with the electric company because that would draw attention to them. So there is a tacit agreement between the parties that a Social Security number must be provided because that’s the rule, but if it happens to be someone else’s Social Security number, well that’s okay.
The funny thing about this is the impact it has to have on the person who was originally assigned that Social Security number by the U.S. government. Rather than hurt their credit it actually helps because there is so much evidence that they are good at paying their bills.
Of course the credit bureau notices something and that’s why they are so able to estimate numbers in the first place. They know what Social Security numbers are being overused and can probably even trace the genealogy of that number as it makes its way across the country. Here’s an amazing fact: some individual Social Security numbers are in use right now by UP TO 3,000 PEOPLE and it isn’t at all unusual for a borrowed number to be used by 200-1,000 people at the same time. [...]