Checking post-conditions in SOA as (or more) important than checking pre-conditions
I agree with Clemens on the postcondition discussion. At the risk of using two quickie "gun/bullet" analogies in a month, I offer this one to explain why checking post-conditions is as (or more) important as checking pre-conditions.
It's better to take the bullets out of the gun, than to wear a bullet-proof vest.
Too often message validation is considered a defensive manuever to protect one's self from bad input. I believe this "knee-jerk" style of coding is an artifact of C and C++ where engineers always check input pointers for nulls and such.
In a system that is constrained by contracts, you certainly know as much about the outgoing messages and inherent contract as the incoming, so there's no reason not validate the outbound messages.
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Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.
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If you get a bad message and carry on regardless, you shoot yourself in the foot.
If you send out a bad message, you shoot someone else in the foot.
So naturally people are going to worry more about the first case than the second. ;)