Mopsos

A city is not a tree from Christopher Alexander is really an inspiring paper for all people designing social spaces, whether in the physical world or in the cyberworld. It support my claim that Personal KM tools and Enterprise KM tools are born from two very different business models.

Christopher focuses on cities, i.e. physical living spaces of large communities of human beings. But I think the same reasoning applies to other human communities of the cyberworld. It also applies to those large communities that are both physical and virtual like global companies.

Christopher starts by defining two social structures the "semilattice", and the "tree"

The semilattice axiom goes like this: A collection of sets forms a semilattice if and only if, when two overlapping sets belong to the collection, the set of elements common to both also belongs to the collection.

The tree axiom states: A collection of sets forms a tree if and only if, for any two sets that belong to the collection either one is wholly contained in the other, or else they are wholly disjoint.

I other words, a semilattice looks like this and a tree looks like that. He then argues that modern societies form an open social structure that is a semilattice, not a tree.

In a traditional society, if we ask a man to name his best friends and then ask each of these in turn to name their best friends, they will all name each other so that they form a closed group. A village is made up of a number of separate closed groups of this kind.

But today's social structure is utterly different. If we ask a man to name his friends and then ask them in turn to name their friends, they will all name different people, very likely unknown to the first person; these people would again name others, and so on outwards. There are virtually no closed groups of people in modern society. The reality of today's social structure is thick with overlap - the systems of friends and acquaintances form a semilattice, not a tree

He then observes that all artificial cities designed from scratch by urban designers and planners like Brasilia or Chandigahr reproduce a tree structure

because the mind's first function is to reduce the ambiguity and overlap in a confusing situation and because, to this end, it is endowed with a basic intolerance for ambiguity - that structures like the city, which do require overlapping sets within them, are nevertheless persistently conceived as trees.

The conclusion of the paper is ominous:

When we think in terms of trees we are trading the humanity and richness of the living city for a conceptual simplicity which benefits only designers, planners, administrators and developers. Every time a piece of a city is torn out, and a tree made to replace the semilattice that was there before, the city takes a further step toward dissociation.

In any organized object, extreme compartmentalization and the dissociation of internal elements are the first signs of coming destruction. (...)

For the human mind, the tree is the easiest vehicle for complex thoughts. But the city is not, cannot and must not be a tree. The city is a receptacle for life. If the receptacle severs the overlap of the strands of life within it, because it is a tree, it will be like a bowl full of razor blades on edge, ready to cut up whatever is entrusted to it. In such a receptacle life will be cut to pieces. If we make cities which are trees, they will cut our life within to pieces.

[through Lilia, again. Thanks, Lilia. By the way, if you finally decide to come to visit Paris, let me know ahead of time]

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