Thursday, August 16, 2007

Edge cases and highways

You are on a highway driving on the fast lane. The middle lane appears free so you signal and shift lane. Switching lane is very common. And when the destination lane is free then everything will go well. Right?
That's right most of the time. In a few rare cases, we are up for the fear of our life. Check the photo. A car in the slow lane moves into the middle lane at the exact same place and time as we do. The two cars get dangerously close to each other and usually both drivers recognize the danger and violently pull back to their respective lanes. Is the other driver doing something wrong? Not at all. He or she also carefully observed the middle lane and it is empty. Only you are still on the fast line. Neither of you saw each other until you both moved into the middle lane.

We call these rare but dramatic situations edge cases. They are rare but the consequences can be severe. Engineers can be tempted to cut the corners and ignore them. If they are very honest they call their product a prototype or a beta. If unexpected the edge case is called a bug or defect. Scientists observe nature and sometimes notice irregularities they can't explain. They discard the results as invalid. A few hundred years later other scientists redo the experiments with better tools and a more open mind - and uncover a new branch of science and series of new natural phenomenas.

Other examples
Which other edge cases have you heard of?

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