Yes it’s that old knotty problem again! Over at gapingvoid.com Hugh MacLeod is fond of using Venn diagrams to illustrate overlapping concerns so here’s one that I recently used for addressing the eternal architecture versus design debate that was the source of much discussion at a recent Architecture Thinking class I was giving.

As I remember it the discussion went something like this:

• Student: So what’s the difference between architecture and design? It seems from what you’re saying its just a matter of scale?
• Me: Whilst its true to say that architecture addresses the major components of the system, rather than the detail, it’s more than that. The architecture is the bridge between the “what” (that is the requirements) and the “how” (that is the design).
• Student: Yeah but isn’t that we usually call “high-level design”.
• Me: Not really. Grady Booch says: “All architecture is design but not all design is architecture”. (I cheated and looked up this quote afterwards and found that Booch goes on to say “architecture represents the significant design decisions that shape a system, where significant is measured by cost of change.”). In my experience high-level design is just the the view that allows the complete system to be represented on one page.
• Student: I still don’t see what the difference really is.
• Me: Okay, here’s the real difference for me (at this point I draw the above Venn on a flip-chart). As well as defining the structure of the system, architecture must also embrace the “what” and the “how” of that structure.  The “what” in this context is the requirements (functional and non-functional) and so architecture involves reasoning about and resolving these sometimes conflicting requirements. It’s about addressing those architecturally significant requirements (the “what”) that will drive (and constrain) the “how” (the design).

Now, if I was drawing this again (and maybe I’ll do this next time) I would actually draw a third overlapping circle which I’d label the “why”. This is where we’d capture the rationale for why we make the (architectural) decisions we do.

Thanks Hugh, this is a neat way of explaining the way things are!