Degrees of coupling

Over the past few years we've seen the distributed system industry moving to embrace loose coupling as though it's a global panacea to all of the woes of the previous decades. I've said on many occasions that coupling (loose or close) is something that cannot be taken in isolation: as with most things there's a trade-off to be made and there are degrees of coupling (no innuendos intended). I made that point again with my first presentation of 2008 and as recently as QCon, also taking that opportunity to point out again that loose coupling isn't something discovered or invented by the distributed systems community. It's a general software engineering pattern that has been used since Noah used his ZX76BC.

Now what makes me write about this again, when it's old hat? Well Jim's written a nice piece on coupling and cohesion. It's worth a read, but what prompted me to add this entry wasn't the subject itself but the fact that it references Pete Lee. As with Jim, Pete was one of my undergraduate teachers and took me through two years of software engineering. And it was this course that first brought loose coupling and cohesion (and many other things) to my attention. When I was preparing my presentation for the winter school I wanted to pull some specific references from the software engineering book we used during that undergraduate course, but it's stuck up in the loft and I was too lazy to go and find it. It's been over 20 years since I last saw it, but I'm pretty sure it was the first edition of Ian Sommeville's excellent book. Maybe time to buy the latest edition!