I was doing some UML diagramming last night with two other programmers, we were able to effectively model the conceptual design of our system using Use Cases. We already had some requirements jotted down on paper (as most people do), but it was amazing to see how much ambiguity there was with the requirements, we all had different ideas of how to go about common tasks.

The Use Cases helped us to clear up those inconsistencies, we didn't get it finished, but for the hour or two that we put in we got a lot back, and I know that the time we would have lost through our misunderstandings would have run higher than those 2 hours spent.

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Any fool can write code that a computer can understand. Good programmers write code that humans can understand.