I have some sympathy for Alan Kay’s “biological analogy” that software could be constructed to resemble biological cells, with each component having a clearly defined barrier (cell membrane) and ability to act autonomously as well as collaboratively. This is, after all, how agent-oriented languages should work too. However, the analogy can clearly only be taken so far. A human cell contains around 6 billion base pairs of DNA, each of which can store a maximum equivalent of 2 bits of information. This gives a total theoretical storage capacity of 12e9 bits or 1.5e9 bytes — roughly 1.4GB, or slightly less than an iPod shuffle. In computational terms, that’s quite a lot. Furthermore, this information is redundantly duplicated on a massive scale within every single cell of your body, and largely duplicated between individuals even of separate species. If this were a computer system, it would be a hugely inefficient and anti-modular one. By modern software engineering standards, a cellular organism is a jumble of duplicate components, each of which is a monolithic mess of spaghetti code!
Nevertheless, I do believe there is still much value in this analogy. After all, as Kay would point out, biological systems are much more sophisticated* than anything we can yet build, and generally much more resilient too. But we must be careful in pursuing such analogies, as the design goals of evolution are different to our own. While evolution can dispense with the intelligent designer, we cannot! And those intelligent designers have their limits. They need to be able to revisit design decisions and update running systems to correct flaws, optimise performance, adjust to new challenges, etc. Modularity is crucial to these tasks. If there is a God, He is not a software engineer.
PS – I recognise that Kay himself is well aware of these limitations of the analogy, as is abundantly evident in the wonderful design of Smalltalk.
* NB: I much prefer the term “sophisticated” to “complex”: the former is perhaps a goal worth pursuing, the latter should be minimised or eliminated.
Neil Madden 