Clay Shirky comes out with a very comprehensive paper on web content ontology and he goes to the extent of analyzing the likes of Periodic table classification, yahoo information architecture, del.icio.us mechanisms to come to the conclusion that ontology is overrated. Extracts with edits and comments from a near 25 page heavy stuff article.
On Tagging :Many of the ways we're attempting to apply categorization to the digital world are actually a bad fit, because we've adopted habits of mind that are left over from earlier strategies. What we're seeing when we see the Web is actually a radical break with previous categorization strategies, rather than an extension of them. Our current categorization schemes allow, based on two units - the link, which can point to anything, and the tag, which is a way of attaching labels to links. The strategy of tagging – free form labeling, without regard to categorical constraints - seems like a recipe for disaster, but as the Web has shown , one can extract a surprising amount of value from big messy data sets.
On Browse Vs Search :Browse versus search is a radical increase in the trust we put in link infrastructure, and in the degree of power derived from that link structure. Browse says the people making the ontology, the people doing the categorization, have the responsibility to organize the world in advance. Given this requirement, the views of the catalogers necessarily override the user's needs and the user's view of the world. If you want something that hasn't been categorized in the way you think about it, you're out of luck. The search paradigm says the reverse. It says nobody gets to tell you in advance what it is you need. Search says that, at the moment that you are looking for it, we will do our best to service it based on this link structure, because we believe we can build a world where we don't need the hierarchy to coexist with the link structure.
On Categorisation :A lot of the conversation that's going on now about categorization starts at a second step - "Since categorization is a good way to organize the world, we should..." But the first step is to ask the critical question: Is categorization a good idea? We can see, from the Yahoo versus Google example, that there are a number of cases where you get significant value out of not categorizing. Even Google adopted DMOZ, the open source version of the Yahoo directory, and later they downgraded its presence on the site, because almost no one was using it. When people were offered search and categorization side-by-side, fewer and fewer people were using categorization to find things.
On Tags: As you can see here, the characteristics of a del.icio.us entry are a link, an optional extended description, and a set of tags, which are words or phrases users attach to a link. Each user who adds a link to the system can give it a set of tags - some do, some don't. Attached to each link on the home page are the tags, the username of the person who added it, the number of other people who have added that same link, and the time. Tags are simply labels for URLs, selected to help the user in later retrieval of those URLs. Tags have the additional effect of grouping related URLs together. There is no fixed set of categories or officially approved choices. You can use words, acronyms, numbers, whatever makes sense to you, without regard for anyone else's needs, interests, or requirements.
On Tags & Conclusion:The addition of a few simple labels hardly seems so momentous, but the surprise here, as so often with the Web, is the surprise of simplicity. Tags are important mainly for what they leave out. By forgoing formal classification, tags enable a huge amount of user-produced organizational value, at vanishingly small cost. The tag overlap is in the system, but the tag semantics are in the users. This is not a way to inject linguistic meaning into the machine. It's all dependent on human context. This is what we're starting to see with del.icio.us, with Flickr, with systems that are allowing for and aggregating tags. The signal benefit of these systems is that they don't recreate the structured, hierarchical categorization so often forced onto us by our physical systems. Instead, we're dealing with a significant break - by letting users tag URLs and then aggregating those tags, we're going to be able to build alternate organizational systems, systems that, like the Web itself, do a better job of letting individuals create value for one another, often without realizing it.
Category : Tags