Conway’s Law and Your Source Tree

Posted by mitch on February 05, 2014

In the last post, I mentioned Conway’s Law:

organizations which design systems […] are constrained to produce designs which are copies of the communication structures of these organizations.

Dr. Conway was referring to people in his article–but what if we substitute “organization” with your product’s source tree and “the communication structures” to how functions and data structures interact? Let’s talk more about Conway’s Law in the context of source tree layout.

Many products of moderate complexity involve multiple moving parts. Maybe a company has a cloud service (back end) and a Web UI (front end). Or a back end and a mobile front end. Or a daemon, some instrumentation scripts, and a CLI. Or a firmware and a cloud service.

I’ve had my hands in a number of companies at various depths of “hands in.” Those who lay out a source tree that fully acknowledges the complexity of the product as early as possible tend to be the ones who win. Often, a company is started to build a core product–such as an ability to move data–and the user interface, the start-up scripts, the “stuff” that makes the algorithm no longer a student project but a product worth many millions of dollars–is an afterthought. That’s fine until someone creates a source tree that looks like this:


What’s wrong here? Presumably, some of the code in util.c could be used in other places. Maybe some of the functions in error.c would be handy to abstract out as well. An arrangement like this in which the cool_product is a large monolithic app likely means it’s going to be difficult to test any of the parts inside of it; likely modules and layering are not respected in a large monolithic app. (Note that I am not saying it’s impossible to get this right, but I am saying it’s unlikely that tired programmers will keep the philosophy in mind, day in and day out.)

A slightly different organization that introduces a library might look as follows:

			Unit tests for the lib/ stuff
		Build scripts or related stuff required,
		code generation, etc.

As a side effect, we can also improve testing of the core code, thus improving reliability and regression detection. Ideally, the cool_product is a small amount of code outside of libraries that can be unit tested independently.

More than once I’ve heard the excuse, “We don’t have time to do this right with the current schedule.”

“I don’t have time for this” means “This isn’t important to me.” When you say, “I don’t have time to clean up the garage,” we all know what you really mean.

I was incredibly frustrated working with a group who “didn’t have time” to do anything right. Years later, that company continues to ship buggy products that could have been significantly less buggy. A few weeks of investment at the beginning could have avoided millions of dollars of expense and numerous poor reviews from customers due to the shoddy product quality. And it all comes back to how hard (or easy) it is to use the existing code, i.e., the communication structure of the code.

If you don’t have time to get it right now, when will you have time to go back and do it right later?

Getting it right takes some time. But getting it wrong always takes longer.

Teams with poor source tree layout often end up copying and pasting code. Sometimes a LOT of code. Whole files. Dozens of files. And as soon as you do that, you’re done. Someone fixes a bug in one place and forgets to fix it in another–over time, the files diverge.

If you’re taking money from investors and have a screwed up the source tree layout, there are two ethical options:

  1. Fix it. A week or two now will be significantly cheaper than months of pain and glaring customer issues when you ship.
  2. Give the money back to the investors.

If you’re reading this and shaking your head because you can’t believe people paint themselves into a corner with their source tree layouts, I envy you! But if you’re reading this and trying to pretend you don’t face a similar position with your product, it might be time to stop hacking and start engineering by opening up the communication paths where they should be open and locking down the isolation and encapsulation where they should not. This holds true for any language and for any type of product.

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