Excitatory dependencies

Yesterday, I read Steven Strogatz’ Nature article, Exploring Complex Networks (PDF), in which he says that “networks are inherently difficult to understand,” and lists a few reasons for this, among which I found the following interesting:

Connection diversity: the links between nodes could have different weights, directions and signs. Synapses in the nervous system can be strong or weak, inhibitory or excitatory.

As I discussed software as networks with my friend Olof, we came up with the idea that the links should have weights determined by the extent that one node knows about the other – that is, what size is the fraction of the other object’s interface that the first object depends upon. We envisioned change as a signal propagating across the network, being reduced on the way by the “resistance” of the links (as in electrical wires). Olof associated this with the neurons in the brain, but I’m not sure whether he thought about how synapses, besides inhibitory also can be excitatory.

I wonder whether this could have relevance for software networks? I think it might. Say that a change is made to an object. As the change affects other objects, it propagates like a signal across the dependency web, fading out as the “resistances” of the “wires” reduce the signal. But in some places in the network, the signal might be amplified, because link that it travels across leads to an object which is very heavily used by the object the signal has just passed. This feels intuitive to me, that a seemingly harmless change (in a not perfectly healthy system) can result in changes cascading in a degree that no-one could imagine.

Perhaps software networks has some things in common with the neural networks in the brain? It might be worth investigating further. As for the Strogatz paper, it doesn’t seem to contain much that isn’t in Linked – but it is two years old, so that’s not much of a surprise.

The above was posted to my personal weblog on February 8, 2003. My name is Peter Lindberg and I am a thirtysomething software developer and dad living in Stockholm, Sweden. Here, you’ll find posts in English and Swedish about whatever happens to interest me for the moment.


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