[crosspost from my DDJ blog]

In a comment to my previous post on Architecture vs. Design, Yoni said:

It seems you are categorizing technical issues as architecture and logical issues as design. I think Martin Fowler's definition of "Making sure important things remain decoupled and easy to change" transverses both categories and is easier to follow.

I have a few things to say about this.

First, I don't categorize technical things as "architectural" and logical ones as "design." What I do say is both "architecture" and "design" are types of design where with one you focus on the wider aspects of the solution and quality attributes, while with the other you focus on local and functional aspects.

I don't see how the definition Yoni brings up is a better way to distinguish between the two? Who is to say what is important and what is not? Isn't decoupling an important trait at all level including so called "detailed design" level (e.g. utilizing dependency injection at the class level will give you better testability). Moreover, decoupling is important but sometimes you need to trade that to be able to satisfy a more prioritized quality attribute (if you want to meet a projec's quality, budget and schedule targets); see my definition of what software architecture is.

Another thing is that it doesn't matter that much where the line between architecture and design passes. The distinction between architecture and design is a semantic one that reminds us that the design of a system needs to be done in several levels of abstraction (provided the system is not too trivial). We need to abstract certain aspects of the system in order to be able to grasp the big picture. You cannot (well, I can't anyway) think at a 100 man-years project. You can only think about it at the class level and understand how everything will work together. Again, architecture is there to remind us to focus on a level of abstraction that lets you deal with non-local decisions and to make sure quality attributes are met if we cross the line to design -  No biggie.