Real World Hierarchy Example

Vehicle Registration in the U.K

The vehicle registration in the U.K. is based on a mixture of letters and numbers. Originally it was one to three letters, followed by some numbers e.g. XYZ123. That worked for a while and then they ran out, and started doing different things. All the while the idea was that a registration was a unique reference to a vehicle.

Then someone spotted that some of the registrations made words or peoples initials, and a market grew up. People bought old worthless cars for the registration, and transferred it to another vehicle. This was unofficial for a while, but then the government agency realised that there was money to be made selling personalised registration numbers.

There is now an offical way of buying, and one for doing the transfer from one vehicle to another.

How can that be catered for in a computer system which has to keep track of vehicles, for the purpose of taxing, checking insurance and testing? With difficulty, I guess.

Personalised number plates are also used as a marketing tool e.g. T16KET seen on a car advertising on line ticket sales.

-- JohnFletcher

In the U.S., license plate numbers are almost always combined with make, model, and color when trying to identify a vehicle. There are also VIN numbers, inspection stickers, titles, insurance, and the driver's license to be checked depending on the circumstances.

Even if it wasn't legal, people can easily steal/switch license plates, or they can fall off when a screw works its way out. So they're not sufficient for identification anyway, for anything other than identifying the plate itself, that is.

VIN numbers are better, but not perfect since they had no standard format until recently and there's the issue of parts.

I worked for a contractor to California's Department of Motor Vehicles once. We were told not to assume license place numbers were unique because somebody fouled up the tracking system a decade or so ago and bunches of duplicates were accidentally released to the public. It was decided it would be cheaper to live with the duplication rather than manage a recall. However, it made accurate data processing a bear.

CategoryHierarchy