While preparing a talk on module systems and architectures I remembered some old talks I listened to talking about architectures and arguing why an explicit software architect is necessary within professional projects. Many of them used the analogy of building a dog-house versus building a cathedral. For a small dog house, you don't need an architecture. But for the cathedral you do. Hm, agree, but where is the point?
I think the world has changed. Today for most software systems the analogy of building something like a cathedral is no longer a good choice. And I hope that people no longer have a cathedral in mind when designing software. We have learned that building software is a learning process, that requirements change all the time, that we need a short time-to-market, and most of all that we need feedback all the time - and react to this feedback quickly. Agile methods reflect this and allows us to move forward to modern ways of software development.
But our view on architectures need to reflect this. Modern software architectures need to be build for flexibility, for changing requirements all the time, for changing even fundamental layers of our software in a flexible way without causing tremendous costs. Having a cathedral in mind don't help you here. But if you still like the analogy of building real buildings (even though I think this is not always a good analogy to building software at all), you should take a look at some modern office buildings. Maybe they are not as beautiful as some of the old cathedrals, but they are built for flexibility.
But building flexible architectures is not an easy task. We need to build a flexible architecture and at the same time just what we need without designing all possible stuff upfront. Sounds like contradictory goals, eh? Hm, in some way, they are. I think modularity can help you to solve this conflict. Modularity (and I mean modularity on a higher level than individual classes or packages, but more something like Bundles in OSGi) helps you to think about dependencies, coupling, cohesion, and many of these nice design principles. And I think we all agree on having a good, decoupled design makes life easier when things change - and they will change.
Last friday I was invited to give a talk at the
Meet-the-Experts event in Solingen. I talked about my view on architectures in an agile world and how module systems drive those architectures for a flexible future. Here are the slides:
Together with my colleague
Stefan Roock I wrote an article on building architectures in an agile way for
the current issue of the German ObjektSpektrum magazine. The article is part of a controversy with Thomas Lieder about how to incrementally build architectures in agile projects.
In the introductory part of the controversy we talk about the basics of agile methods and the goal of keeping a flat cost curve for features over a long period of time. To achieve this goal we need to change and refactor the software all the time. This is an integral part of agile software development. We learned that its not possible to foresee the future and therefore decided to design only the next steps - and refactor, if we learn over time and find better designs if new requirements appear. This is quite clear on the low-level of individual classes and nicely supported by test-driven development and refactoring tools.
If we use the same argumentation for the architecture of a project, the discussions get a lot more controversy. People don't believe that it is easy to change and refactor the architecture of a system incrementally and flexible over time. We found this discussion often times quite unstructured and using the term architecture in various flavors and meanings. To ease the discussion about agile architectures we divide between the basic architectural style and the concrete architecture of a concrete system. Our opinion is that the basic architectural style is hard to change over time (for example changing a system from a standalone-rich-client application into a multi-user app-server-based system could be quite hard). In contrast to this we believe that changing the concrete architecture and structure of a system could be done incrementally and agile over time. This is obviously not true for every application. They need to be build from ground-up for flexibility and change. But how to build a system that is easier to change over time, even on the architectural level?
From our point of view, there are three fundamental characteristics of design you need to remember every day to build flexible architectures:
understandable,
loosely coupled and
free of redundance. There are many well-known design principles that helps you to build such systems. Keep them in mind, build loosely coupled components, think about good APIs between them - and you are on the right track to build flexible applications and flexible architectures.
A few days ago I gave a
short talk on Incremental Design at
SEACON 2009, a new buzzword-free conference in Hamburg, Germany. Aside of the fact that this was the first conference in my beautiful home town (and only 15min away from home), I enjoyed to meet a lot of people there. I also made up a few slides for my talk, which you can now download as PDF (in German):
And last but not least I used my new presentation tool called
Session Five for the first time. Was absolutely great!
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