I attended a fantastic talk about big data visualisation at the YOW! 2014 conference in Sydney last month (slides), where Doug Talbott talked about how to understand and visualise large quantities of data. One of the things he mentioned was Shneiderman's mantra:
Overview first, zoom and filter, then details-on-demand
Leaving aside the thorny issue of how teams structure their software systems as code, one of the major problems I see teams having with software architecture is how to think about their systems. There are various ways to do this, including a number of view catalogs (e.g. logical view, design view, development view, etc) and I have my C4 model that focuses on the static structure of a software system. If you inherit an existing codebase and are asked to create a software architecture model though, where do you start? And how to people start understanding the model as quickly as possible so they can get on with their job?
Shneiderman's mantra fits really nicely with the C4 model because it's hierarchical.
My starting point for understanding any software system is to draw a system context diagram. This helps me to understand the scope of the system, who is using it and what the key system dependencies are. It's usually quick to draw and quick to understand.
Next I'll open up the system and draw a diagram showing the containers (web applications, mobile apps, standalone applications, databases, file systems, message buses, etc) that make up the system. This shows the overall shape of the software system, how responsibilities have been distributed and the key technology choices that have been made.
As developers, we often need more detail, so I'll then zoom into each (interesting) container in turn and show the "components" inside it. This is where I show how each application has been decomposed into components, services, modules, layers, etc, along with a brief note about key responsibilities and technology choices. If you're hand-drawing the diagrams, this part can get a little tedious, which is why I'm focussing on creating a software architecture model as code, and automating as much of this as possible.
Optionally, I might progress deeper into the hierarchy to show the classes* that make up a particular component, service, module, layer, etc. Ultimately though, this detail resides in the code and, as software developers, we can get that on demand.
Next time you're asked to create an architecture model, understand an existing system, present an system overview, do some software archaeology, etc, my advice is to keep Shneiderman's mantra in mind. Start at the top and work into the detail, creating a story that gets deeper into the detail as it progresses. The C4 model is a great way to do this and if you'd like an introduction to it (with example diagrams), you can take a look at Simple Sketches for Diagramming Your Software Architecture on the new Voxxed website.
* this assumes an OO language like Java or C#, for example
Simon is an independent consultant specializing in software architecture, and the author of Software Architecture for Developers (a developer-friendly guide to software architecture, technical leadership and the balance with agility). He’s also the creator of the C4 software architecture model and the founder of Structurizr, which is a collection of open source and commercial tooling to help software teams visualise, document and explore their software architecture.