During the Federated Social Web meetup in Berlin a few weeks ago, most folks used the phrases "distributed network" and "decentralized network" interchangeably, which doesn't seem unreasonable at this point in time when both appear in major contrast to the prevailing "centralized network" architecture of Web sites. On my last night in Berlin, on the steps of a crashed space station at around 4am (early flights to catch) I was chatting with Harry Halpin and he had the following diagram on his netbook:
It's from Paul Baran's landmark memo from 1964, "On Distributed Communications: 1. Introduction to Distributed Communications Networks" (see also some related network diagrams), some of the work which eventually led to the development of the Internet.
Harry was quite insistent on the significance of the "decentralized" net, saying that it was the one you found in nature (e.g. plant structure). I suggested that "distributed" looked at lot like (a 2D representation of) biological cell structure. That wasn't a very satisfactory analog, and since I've had my eyes open for a good natural world example of "distributed". Now I think I have one, and while it's in a different dimension than e.g. plant structure I reckon it maps quite nicely onto Web systems.
(in the woods up the hill)
To quote Wikipedia:
Lichens are composite organisms consisting of a symbiotic association of a fungus (the mycobiont) with a photosynthetic partner (the photobiont or phycobiont), usually either a green alga (commonly Trebouxia) or cyanobacterium (commonly Nostoc). The morphology, physiology and biochemistry of lichens are very different from those of the isolated fungus and alga in culture.
Now imagine how these things might have evolved. Initially there must have been an inheritance tree for the fungi and an independent tree for the algae (following the "decentralized" form), but then at some point the organisms started to get benefit from each other (I am not a microbiologist, but I'd guess that it probably started as a parasitic relationship, then the host side evolved some advantage). So there's a structure something like this:
The tree has become a graph. [PS. ok, strictly speaking a tree is already a graph, but you know what I mean]
Analogies get useful when you can use known aspects of one perspective to predict unknown aspects of the other (like the weird old alchemists' "As Above, So Below"). I don't know, vague hand-waving, maybe the nutrient molecules the fungi handle in lichen could be said to correspond to data, the photosynthesis of the algae corresponding to processing.
While clear-cut symbiosis like this isn't exactly the most common relationship in nature, there's obvious interdependence between every kind of organism on this planet. I don't think it's much of a stretch to suggest there are good parallels with Web systems, especially if you view the interfaces between organisms and their environment as corresponding to APIs between online systems. Certainly client tools and services (agents, in other words) correspond nicely to organisms.
The Web of Data (alongside the Web of documents) is already pretty distributed, the Linked Open Data cloud diagram being a nifty representation. This aspect of the Web isn't in itself particularly dynamic in its operation (data usually just sits there, periodically updating). But given the number of processors connected to the Web as servers and clients, the digital environment certainly has the potential for extremely interesting interactions.