Do you have a shared vocabulary?

A common set of abstractions is more important than a common notation

"This is a component of our system", says one developer, pointing to a box on a diagram labelled "Web Application". Next time you're sitting in an conversation about software design, listen out for how people use terms like "component", "module", "sub-system", etc. We can debate whether UML is a good notation to visually communicate the design of a software system, but we have a more fundamental problem in our industry. That problem is our vocabulary, or rather, the lack of it.


I've been running my software architecture sketching exercises in various formats for nearly ten years, and thousands of people have participated. The premise is very simple - here are some requirements, design a software solution and draw some pictures to illustrate the design. The range of diagrams I've seen, and still see, is astounding. The percentage of people who choose to use UML is tiny, with most people choosing to use an informal boxes and lines notation instead. With some simple guidance, the notational aspects of the diagrams are easy to clean up. There's a list of tips in my book that can be summarised with this slide from my workshop.

Some tips for effective sketches


What's more important though is the set of abstractions used. What exactly are people supposed to be drawing? How should they think about, describe and communicate the design of their software system? The primary aspect I'm interested in is the static structure. And I'm interested in the static structure from different levels of abstraction. Once this static structure is understood and in place, it's easy to supplement it with other views to illustrate runtime/behavioural characteristics, infrastructure, deployment models, etc.

In order to get to this point though, we need to agree upon some vocabulary. And this is the step that is usually missed during my workshops. Teams charge headlong into the exercise without having a shared understanding of the terms they are using. I've witnessed groups of people having design discussions using terms like "component" where they are clearly not talking about the same thing. Yet everybody in the group is oblivious to this. For me, the answer is simple. Each group needs to agree upon the vocabulary, terminology and abstractions they are going to use. The notation can then evolve.

My Simple Sketches for Diagramming Your Software Architecture article explains why I believe that abstractions are more important than notation. Maps are a great example of this. Two maps of the same location will show the same things, but they will often use different notations. The key to understanding these different maps is exactly that - a key tucked away in the corner of each map somewhere. I teach people my C4 model, based upon a simple set of abstractions (software systems, containers, components and classes), which can be used to describe the static structure of a software system from a number of different levels of abstraction. A common set of abstractions allows you to have better conversations and easily compare solutions. In my workshops, the notation people use to represent this static structure is their choice, with the caveat that it must be self-describing and understandable by other people without explanation.

Next time you have a design discussion, especially if it's focussed around some squiggles on a whiteboard, stop for a second and take a step back to make sure that everybody has a shared understanding of the vocabulary, terminology and abstractions that are being used. If this isn't the case, take some time to agree upon it. You might be surprised with the outcome.

About the author

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.

You can find Simon on Twitter at @simonbrown ... see for information about his speaking schedule, videos from past conferences and software architecture training.

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