Tuesday, December 04, 2012

The Onion Of Compromise


I love little phrases that sum up large scale behaviours in software systems and the organisations that produce them. One of my favourite is “The Onion Of Compromise.” I first heard this gem from my excellent friend Iain Holder. Iain doesn’t claim to be the author, that honour goes to a mysterious third person named ‘Mike’.

Being a programmer is all about making decisions. Lots and lots of little decisions. In fact every line of code is a decision; a little cog in the wheel of a grander machine. The simple thing that separates a good programmer from a poor programmer is that they tend to make relatively more good decisions and less bad ones.

Incidentally, that’s why it’s a mistake to think that you can hire an experienced ‘chief architect’ who ‘designs’ your system, while rooms full of junior/cheap developers churn out the code - and expect anything other than a disaster to occur. The decisions are just too granular to be  made by one person on a large project.

Good decisions are ones which aid the evolution and stability of an application. They are summed up by epithets that describe general good practice, such as ‘Don’t Repeat Yourself’, ‘Open Closed Principle’ and a hundred others. An experienced programmer will employ a range of these rules-of-thumb to ensure that they don’t get tangled up in needless complexity as their application grows. You can tell a project where good decisions have been made; it’s easy to add new features and there are few bugs.

A bad decision often doesn’t seem like a bad decision at first, merely a way of implementing a feature or fixing a bug with the least possible impact on the code. Often the bad decision will introduce a constraint on further evolution of the software or a special case given a particular combination of factors. If a bad decision isn’t rolled back it can quickly lead to further bad decisions as the programmer works around it. Soon layers of poor design wrap that initial poor decision. This is ‘The Onion of Compromise’. That initial first mistake (or compromise) leads to a cascade of poor choices. Another name for the layers of the onion is ‘Technical Debt’.

It’s easy to spot software that has suffered from The Onion of Compromise; it’s brittle, you change one thing and it breaks seemingly unrelated parts of the system; it seems to take ages to implement new features; and there’s a high bug count.

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