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Thursday, April 7, 2011

Flow Based Programming

Another important concept for productivity improvement is that of a reusable subroutine library. I also believe strongly that reuse is another key piece of the solution, but not exactly in the form in which we visualized it in those days. In company after company, I have seen people start up shared subroutine libraries with a fine flurry of enthusiasm, only to find the action slowing to a standstill after some 30 or 40 subroutines have been developed and made available. Some companies are claiming much higher numbers, but I suspect these are shops which measure progress, and reward their people, based on how many subroutines are created and added to the library, rather than on whether they are actually used. Although organizational and economic changes are also required to really capitalize on any form of reuse, I believe there is a more fundamental reason why these libraries never really take off, and that is the philosophy of the von Neumann machine. I will be going into this in more detail in Chapter 1, but I found I was able to predict which subroutines would land up in these libraries, and it was always "one moment in time" functions, e.g. binary search, date routines, various kinds of conversions. I tried to build an easy-to-use, general purpose update (yes, I really tried), and I just couldn't do it (except for supporting a tiny subset of all the possible variations)! This experience is what got me thinking about a radically different approach to producing reusable code. I hope that, as you read this book, you will agree that there is another approach, and that it is completely complementary to the old one

Rapid prototyping and the related idea of iterative development were (and are still) another enthusiasm of mine. Rapid prototyping is a process of reducing the uncertainties in the development process by trying things out. I believe that anything you are uncertain about should be prototyped: complex algorithms, unfamiliar hardware, data base structures, human interfaces (especially!), and so on. I believe this technique will become even more important in the next few decades as we move into ever more complex environments. Here again, we will have to modify or even abandon the old methodologies. Dave Olson's 1993 book, "Exploiting Chaos: Cashing in on the Realities of Software Development", describes a number of approaches to combining iterative development with milestones to get the best of both worlds, plus some fascinating digressions into the new concepts of chaos and "strange attractors". There are some very strange attractors in our business! I have also believed for some time that most prototypes should not just be thrown away once they have served their purpose. A prototype should be able to be "grown", step by step, into a full-fledged system. Since the importance of prototypes is that they reduce uncertainty, rewriting applications in a different language is liable to bring a lot of it back!

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