I presented two talks last week with the title "Software architecture vs code" - first as the opening keynote for the inaugural Software Design and Development conference and also the next day as a regular conference session at GOTO Chicago. Videos from both should be available at some point and the slides are available now. The talk itself seems to polarise people, with responses ranging from Without a doubt, Simon delivered one of the best keynotes I have seen. I got a lot from it, with plenty 'food for thought' moments. through to "hmmm, meh".
The basic premise of the talk is that the architecture and code of a software system never quite match up. The traditional way to communicate the architecture of a software system is with diagrams based upon a number of views ... a logical view, a functional view, a module view, a physical view, etc, etc. Philippe Kruchten's 4+1 model is an example often cited as a starting point for such approaches. I've followed these approaches in the past myself and, although I can get my head around them, I don't find them an optimal way to describe a software system. The "why?" has taken me a while to figure out, but the thing I dislike is the way in which you get an artificial separation between the architecture-related views (logical, module, functional, etc) and the code-related views (implementation, design, etc). I don't like treating the architecture and the code as two separate things, but this seems to be the starting point for many of the ways in which software systems are communicated/documented. If you want a good example of this, take a look at the first chapter of "Software Architecture in Practice" where it describes the relationship between modules, components, and component instances. It makes my head hurt.
This difference between the architecture and code views is also exaggerated by what George Fairbanks calls the "model-code gap" in his book titled "Just Enough Software Architecture" (highly recommended reading, by the way). George basically says that your architecture models will include abstract concepts (e.g. components, services, modules, etc) but the code usually doesn't reflect this. This matches my own experience of helping people communicate their software systems ... people will usually draw components or services, but the actual implementation is a bunch of classes sitting inside a traditional layered architecture. Actually, if I'm being honest, this matches my own experience of building software myself because I've done the same thing! :-)
My approach to all of this is to ensure that the architecture and code views of a software system are one and the same thing, albeit from different levels of abstraction. In other words, my primary focus when describing a software system is the static structure, which ranges from code (classes) right up through components and containers. I model this with my C4 approach, which recognises that software developers are the primary stakeholders in software architecture. Other views of the software system (deployment, infrastructure, etc) slot into place really easily when you understand the static structure.
To put this all very simply, your code should reflect the architecture diagrams that you draw. If your diagrams include abstract concepts such as components, your code should reflect this. If the diagrams and code don't line up, you have to question the value of the diagrams because they're creating a fantasy and there's little point in referring to them.
This deserves a separate blog post, but something I also mentioned during the talk was that teams should challenge the traditional layered architecture and the way that we structure our codebase. One way to achieve a nice mapping between architecture and code is to ensure that your code reflects the abstract concepts shown on your architecture diagrams, which can be achieved by writing components rather than classes in layers. Another side-effect of changing the organisation of the code is less test-induced design damage. The key question to ask here is whether layers are architecturally significant building blocks or merely an implementation detail, which should be wrapped up inside of (e.g.) components. As I said, this needs a separate blog post.
As I said, the slides are here. Aligning the architecture and the code raises a whole bunch of interesting questions but provides some enormous benefits for a software development team. A clean mapping between diagrams and code makes a software system easy to explain, the impact of change becomes easier to understand and architectural refactorings can seem much less daunting if you know what you have and where you want to get to. I'm interested in your thoughts on things like the following:
Convincing people to structure the code underlying their monolithic systems as a bunch of collaborating components seems to be a hard pill to swallow, yet micro-service architectures are going to push people to reconsider how they structure a software system, so I think this discussion is worth having. Thoughts?
Simon is an independent software development consultant specialising in software architecture and the author of Software Architecture for Developers. Simon lives in Jersey and regularly speaks to audiences around the world. You can find Simon on Twitter at @simonbrown and Google+.