Tim Bray asks a great question: “Are there any questions you want to ask, or jobs you want to do, where tags are part of the solution, and clearly work better than old-fashioned search?”

Here’s my answer, partial and in three parts.

- First, tags keep found things found. Search is about finding things, tags (in the del.icio.us mode) are about keeping them. Like many people, I stopped remembering things when the internets came along, and started remembering pointers to things instead. Many’s the time I’ve wanted to find something I read N months ago, and had to remember whether I saw it on slashboing or blogpop, or I had to recreate a multi-word search on Google. Tags, fby contrast, are thumbtacks with filters.

You could add that functionality to search directly, of course, but a) you’d still do it using tags and b) you’d miss all the places URLs come from when they don’t come from search, like IM, mail, and plain old clicking around. Search centers around the supplier. Tags center around the user, and any technology that recognizes that each user is the center of their world has good adoption characteristics.

- Second, tags add ‘people’ and ‘time’ as cross-cutting elements. del.icio.us provides a measure of social velocity — I have not worked in a development shop for some years, and would have missed the significance of the original Ajax article, but seeing the ferocity of attention on del.icio.us, I knew that something important was going on, not from reading the article, but from reading the userbase. Again, you can imagine adding this sort of thing to search, but you’d do it by watching what people tagged.

This is just one exemple of the ways that the addition of sorting on people+time is valuable. More, much more, is coming, by hanging new kinds of filtering and sorting off of those characteristics, including especially shared awareness among tagging groups, and the subsequent ability to search the group mind.

- Third, a look at the top tags on del.icio.us reveals several that could not work as part of a search. I cannot search directly for things toread, or things that are fun, funny, or cool, because those are in the eye of the beholder. I can’t search directly for tools or reference, because what I consider a tool or a reference work is different from what you do, and people writing things that I might think of as a tool or a reference work rarely label them that way.

That’s (part of) a longer answer — Tim’s question is the right one, and answering it is going to take a lot more effort than this post. The key element, though, is that demand is different than supply, retrieving is different than searching, and keeping is different than finding. Tags are demand-side tools allow us to do things that supply-side tools don’t.

Update (10/3/08): For up-to-date information about me, see my Nature Network profile page.

Hello. I work for Nature Publishing Group (NPG) as head of web publishing. I was once a neurophysiologist working on the cellular mechanisms of associative memory, but I switched from networks of neurons to networks of computers about 10 years ago when I discovered the web. They have more to do with each other than you might think, as Vannevar Bush hinted 50 whole years before my own epiphany:

Our ineptitude in getting at [a] record is largely caused by the artificiality of systems of indexing. When data of any sort are placed in storage, they are filed alphabetically or numerically, and information is found (when it is) by tracing it down from subclass to subclass. It can be in only one place, unless duplicates are used; one has to have rules as to which path will locate it, and the rules are cumbersome. Having found one item, moreover, one has to emerge from the system and re-enter on a new path.

The human mind does not work that way. It operates by association. With one item in its grasp, it snaps instantly to the next that is suggested by the association of thoughts, in accordance with some intricate web of trails carried by the cells of the brain.

Bush’s article is often interpreted (among other things) as anticipating the web. But reading it again now, it looks to me just as much like a prediction of tagging. (To see what I mean, just read Section 7.) Perhaps that’s because hyperlinking and tagging are so similar. Crudely speaking, hyperlinks allow me to associate something I’m creating with something that someone else has created, while tags allow me to associate two things that other people have created.

Or maybe it’s just because tagging is my latest obsession. Unlike other people contributing to this blog, I’ve written little on the subject except for co-authoring one or two recent papers about social bookmarking. But don’t let that mislead you: at NPG we’re into tagging big-time. We’ve created a tagging tool for scientists, released the code and have just begun experimenting with using it in our own editorial processes. I plan to write here about our experiences as we see how far tagging can take us in tackling the (formidable) information organisation needs of modern science. I’m sure it won’t be a panacea (for lots of reasons that I’ll probably write about too), but I’m equally sure it will be an essential part of the answer.

It’s hard to put my finger on, but I guess my faith in tagging arises for similar reasons that my faith in the web emerged a decade ago. It’s liberating, not restrictive; bottom-up, not imposed; relational, not hierarchical. It also cleverly harnesses selfish acts and directs them towards the common good. But most of all, it just seems to fit the way our brains work.