This article; Marc's Voice: Outliners structure editors prompted me to write something I've been considering for a while.

Outliners and Outlining are a very useful technique for getting one's thoughts in order and organising a document or argument in nice, understandable and straight line form. It's a pattern that we've ended up using in many places from XML to DMOZ to directories like Yahoo to bulleted lists.

So why are they harmful? Well when you use a tool that encourages you to think in terms of hierarchies, everything looks like a hierarchy. Unfortunately the world is much much messier than that. Almost everything is actually a mesh not a hierarchy. And when hierachies do exist in the data, it's very likely that you will find 2 or more inherent hierarchies that are orthogonal and in most real world situations it's more like 10. Which leads you to all sorts of mess with regional divisions versus category divisions and the same item being placed in lots of different places in the parallel hierarchies you're forced into using.

To see this in action, you've only got to look at how generally useless DMOZ is for actually finding anything. Or look at Craigslist with it's repeating categories in lots of very artificial regional sites.

I also think this is at the core of the lack of understanding between the XML and RDF camps. The XML people think everything is a hierarchy and when they look at simple RDF that's all they see. The RDF people understand that everything is a mesh and that a hierarchy is a just a special case of a mesh. But because everything is a mesh, there is only arcs, nodes and triples.

I suspect that the move towards anarchic tagging in systems like and Flickr are driven by this tension between mesh and hierarchy as well though I haven't seen it expressed like this. Tag driven systems look horribly uncontrolled to hierarchy people. But they actually reflect the real world much better than hierarchies.

It's very common in the hierarchy world to have big aguments about the structure and content of the category hierarchy which then leads to demands for some centralized control over who can edit the tree or even who can define how a new tree is built. So there's a certain irony here that category hierarchies require a political hierarchy to control them. Mesh based systems avoid this by frequently de-centralizing control over the categories in the mesh right out to the end user.

So in a nutshell, Outliners are harmful because they lead to hierarchy thinking. And hierarchy thinking is harmful because it leads to political hierarchies. And all of this is harmful because the world is actually mess(h)y and not structured into elegant trees.

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[ 21-Nov-04 10:53am ] [ , ]