Saturday, September 13, 2008


I’ve been facing some small, tough design problems lately: relatively simple cases where finding a good solution is surprisingly hard. As usual, it’s trivial to come up with something that “works”; it’s also quite simple to come up with a reasonably good solution. It’s hard to come up with a great solution, where all forces are properly balanced and something beautiful takes shape.

I like to think visually, and since standard notations weren’t particularly helpful, I tried to represent the problem using a richer, non-standard notation, somehow resembling Christopher Alexander’s sketches. I wish I could say it made a huge difference, but it didn’t. Still, it was quite helpful in highlighting some forces in the problem domain, like an unbalanced multiplicity between three main concepts, and a precious-yet-fragile information hiding barrier. The same forces are not so visible in (e.g.) a standard UML class diagram.

Alexander, even in his early works, strongly emphasized the role of sketches while documenting a pattern. Sketches should convey the problem, the process to generate or build a solution, and the solution itself. Software patterns are usually represented using a class diagram and/or a sequence diagram, which can’t really convey all that information at once.

Of course, I’m not the first to spend some time pondering on the issue of [generative] diagrams. Most notably, in the late ‘90s Jim Coplien wrote four visionary articles dealing with sketches, the geometrical properties of code, alternative notations for object diagrams, and some (truly) imponderable questions. Those papers appeared on the long-dead C++ Report, but they are now available online:

Space-The final frontier (March 1998)
Worth a thousand words (May 1998)
To Iterate is Human, To Recurse, Divine (July/August 1998)
The Geometry of C++ Objects (October 1998)

Now, good ol’ Cope has always been one of my favorite authors. I’ve learnt a lot from him, and I’m still reading most of his works. Yet, ten years ago, when I read that stuff, I couldn’t help thinking that he lost it. He was on a very difficult quest, trying to define what software is really about, what beauty in software is really about, trying to adapt theories firmly grounded in physical space to something that is not even physical. Zen and the Art of Motorcycle Maintenance all around, some madness included :-).

I re-read those papers recently. That weird feeling is still here. Lights and shadows, nice concepts and half-baked ideas, lot of code-centric reasoning, overall confusion, not a single strong point. Yeah, I still think he lost it, somehow :-), and as far as I know, the quest ended there.
Still, his questions, some of his intuitions, and even some of his most outrageous :-) ideas were too good to go wasted.

The idea of center, that he got from The Nature of Order (Alexander’s latest work) is particularly interesting. Here is a quote from Alexander:
Centers are those particular identified sets, or systems, which appear within the larger whole as distinct and noticeable parts. They appear because they have noticeable distinctness, which makes them separate out from their surroundings and makes them cohere, and it is from the arrangements of these coherent parts that other coherent parts appear.

Can we translate this concept into the software domain? Or, as Jim said, What kind of x is there that makes it true to say that every successful program is an x of x's?. I’ll let you read what Jim had to say about it. And then (am I losing it too? :-) I’ll tell you what I think that x is.

Note: guys, I know some of you already think I lost it :-), and would rather read something about (e.g.) using variadic templates in C++ (which are quite cool, actually :-) to implement SCOOP-like concurrency in a snap. Bear with me. There is more to software design than programming languages and new technologies. Sometimes, we gotta stretch our mind a little.

Anyway, once I get past the x of x thing, I’d like to talk about one of those wicked design problems. A bit simplified, down to the essential. After all, as Alexander says in the preface of “Notes on the Synthesis of Form”: I think it’s absurd to separate the study of designing from the practice of design. Practice, practice, practice. Reminds me of another book I read recently, an unconventional translation of the Analects of Confucius. But I’ll save that for another time :-).


Unknown said...

I think it’s absurd to separate the study of designing from the practice of design. Practice, practice, practice

Ok, this makes me think about a good way to practice and learning something. My idea was to start up a blog where I explain the design of a software application. It'd be a good idea if some experienced designers (not only Carlo, He's overloaded I think :)) could give me some suggestions time after time. The first one could be an idea about what type of software to design :) (maybe something useful in practice). Hope to hear some voices...:)

Carlo Pescio said...

I could certainly propose a few interesting / useful design problems. Do you also plan to implement whatever you'll design?

A first proposal, straight from my past few days of consulting: a mutation testing engine for the entire family of C-like languages (C, C++, Java, C#). The downside (or upside :-) is that one has to learn about mutation testing first...

Oh, and just yesterday I thought of an interesting way to visualize classes, but I would need a special tool, similar to an N-dimensional particle simulator. This is quite simple to design, I guess, once we get requirements right :-). Implementation could take a while, though. More about this only after the X of Xs thing, as it is somehow related.

Unknown said...

Even if I will focus on design, Is's always a good idea to test what I'm doing (to implement a design is a good test I think :).

The two proposal are equally mysterious to me. Well, I think I'll wait for the post about the second problem, in the meantime I will read something about mutation testing. Then I'll make a decision!