John Hiler’s piece on the death of hierarchy is startling. He compares the diminishing value of folder-based navigation and organization in three applications: Web directories, email, and the filesystem. It’s at once a history of user interfaces and an obituary for the virtual folder.

Admittedly, I started reading the article with skepticism. The folder dead? Can it be true? Hogwash! And then Hiler smacked me upside the head, quoting from *my* Boxes and Arrows article on Gmail, in which I describe my ironic and sad email-folder-phobia. Gulp.

The folder metaphor is a strange one because virtual folders behave almost nothing like actual folders. The other day, for example, I tried dragging and dropping a folder into an email message. Everything I had for a particular project is in that folder and I needed to send all the documentation to someone. With a real folder, I could just drop it on the person’s desk. With the virtual folder, Outlook coughed this up:

Hiler is right to point out that folder-based navigation is going away, but I think it’s dangerous to extend the demise of the folder (a bad metaphor) to the demise of hierarchy and formal structure. There is still a place for formal structure in interface design, even if it doesn’t look or behave like our old friend the folder.

It’s also dangerous to compare “hierarchy” with “search.” Hierarchy is, most typically, a part-whole organization of things. Search, on the other hand, is a behavior where users specify some criteria and the computer does the work of locating objects that share something in common with them. These two notions are hardly mutually exclusive. Perhaps Hiler meant to compare search with browse, a behavior where users select from menus of options to arrive at the desired thing.

In Hiler’s three “search” case studies, there is evidence of formal structure, though it’s under the surface. With Gmail, for example, there’s still the notion of a thread which contains messages. There is an inbox and an archive, which contain threads. There are relationships between original messages and replies. These are abstract hierarchies that are inherent to the information architecture, not layered on top like a folder structure. They may seem self-evident, but constructing these hierarchies requires a careful, user-aware design process.

With desktop search applications like Google’s or Apple’s Spotlight, there is also an underlying structure and hierarchy that drives that functionality: the metadata associated with the files in the filesystem. By using these data, desktop search engines can, in a sense, create hierarchies on the fly. People can create “temporary folders” so to speak by doing searches. Hierarchies aren’t disappearing, they’re just becoming incorporated into interfaces transparently. A computer can leverage the power of a hierarchy better than a human can.

But user-defined hierarchies persist. A creative director from frog design in this Wired article suggests that browsing systems are being built into more and more applications like iTunes and iPhoto. By opening an app, the user has narrowed down the kinds of files he’s interested in. Users can define hierarchies for these individual applications without having to define a hierarchy that suits their entire library of files.

There’s no doubt that folders have over-stayed their welcome as an affordance for manipulating files, but that’s not to say users do not desire structure. A great analysis by Tom Coates hints at an emerging trend in free-tagging. Coates rightfully suggests that the evidence is hardly definitive, but it’s too compelling to dismiss. Looking at the del.icio.us tags applied to his site over time, he noticed that the tag “blogs” was in decline while the tag “blog” was increasing. While users initially thought of tags as folders (”I’ll put Tom’s blog in my ‘blogs’ tag”), now they think of them more as labels. Here’s my visual representation of Coates’ notion:

If we can accept Coates’ theory at face value, the notion of a folder is losing ground. But people are not ignoring metadata altogether. They recognize the value of making sure they can find things again. They don’t trust their ability to find something by simple search, so they add information to make it more accessible. They are, in a sense, imposing structure on a corpus by tagging it. Recognizing that a single entry in that corpus can “have” multiple tags, and that each tag “has” one or more entries associated with it, indicates that users understand the implied hierarchies there.

Hierarchies are not dead. We may use them as we did when personal computers first came out, to organize a small amount of information. By limiting the scope of information, a user-defined hierarchy becomes useful. We may use them as temporary containers, like a collection of search results. We may use them to organize the elements of an information system (like email). We may find new ways to add meta data to information to allow us to create as-needed hierarchies. The human mind loves part-whole organization, even if its abstract and complex. While interfaces may do away with simple implementations (like folders) we will never see them disappear completely.