Re: [xml-dev] Use-cases are the bane of orthogonality

[Michael Kay <mike@saxonica.com>]

> 
> Michael Kay wrote this extraordinary statement: [2]
> 
> 	Use-cases are the bane of orthogonality. Any system with 
> 	good orthogonality can do things for which it is very difficult 
> 	to find a use case. Design focused excessively on use-cases 
> 	leads to a lack of orthogonality.
> 
> Then, without focusing on use-cases, how does one approach design? Is this the right approach: Develop a few use-cases for inspiration and then work on creating simple components that can be connected to any other component?
> 

That’s one way. Another way is this: create the simplest possible design (e.g. the design that can be described in fewest words) that satisfies all the use cases, and refuse to accept restrictions that reduce the orthogonality of this design even though the restricted design still satisfies all the use cases.

Example: use cases indicate that you need to accept payment from suppliers in USD or EUR, but you need to pay your own suppliers in USD or GBP. The system has greater orthogonality if all money amounts can be in any currency. Go for the more general solution. If your paymasters insist on the restriction, implement the restriction cosmetically, such that it can easily be removed.

Michael Kay
Saxonica