7 October 2009

Agile and Architecture

I have read and heard several "observations" on how to incorporate a guiding architecture in the current trend of having agile S/W development. There seem to be a lot of smoke but not so much substance, but I will try to summarise a few points which I have concluded through the smoke.

Caveat: My background is in automotive software, and there seems to be no business domain which is less agile than automotive...

Architecture is up-front design, so if no upfront design is important in you agile practice, then I claim the architecture will rather be manifested by your code than the result of making concious decisions between architectural alternatives. The question is if you could have a light architecture so that you avoid a big upfront design (BUD) and allow the architecture to evolve in parallel with the software while it still guides and controls the software development.

Most agile practices focus on delivering the functional behaviour (use cases, user stories, or whatever), which drives the software. Contrary to this architecture focuses on satisfying the non-functional properties as well, i.e. quality attributes which usually are system-wide. I think deciding between these two focuses is really a business decision on how you want the team to work. If the former is more important then you don't have the same need of someone preforming the role of an architect. If the latter is important it will be difficult to succeed if you don't empower them.
I have heard studies of agile practitioners that claim that non-functional properties are solved in re-factoring (for example one study by M.A. Babar at the experience track at the WICSA 2009 conference). I claim that some properties cannot be solved by re-factoring, for example in the development of safety-critical systems. But agile practices should perhaps never be used for development of those?

There seem to be a trend to use agile synonymous with no or little documentation. I don't mind having small architecture descriptions (AD). A possible problem: If the rationale is omitted to make the AD smaller, I think the value of the AD will be significantly less.

If I read the Agile Manifesto there is nothing that says you should de-emphasise a guiding architecture...

Some texts, blogs and presentations can be found with a little googling:
Software Architecture and Agile Software Development —An Oxymoron? by P Kruchten
Agile Architecture: Strategies for Scaling Agile Development by Scott W Ambler
Software Architecture-Centric Methods and Agile Development by Nord and Tomayko
The Formal Goodness of Agile Software Architecture, part 1 and part 2 by Dave Langer
Architecture Meets Agility by Hakan Erdogmus in IEEE Software

There is also a forthcoming book with the title "Lean Software Architecture" by Coplien and Bjørnvig, forthcoming in May 2010. They have some interesting links and excerpts on their website.

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