John Hiler has an interesting post on Microcontentnews called Google’s War on Hierarchy, and the Death of Hierarchical Folders. He talks about how that computing standby the folder is being replaced by search and tags:

Hierarchical Folders have helped us manage information for decades. They’ve proven themselves as some of the most flexible tools ever created: organizing wildly different industries, from Web Directories, to Email and Desktop File Systems.

But Folders rarely solve the core problem that they address - and often create new ones, like forcing you to create new folders just to manage new information. Solutions like Search, Archives, Stars and Labels get more directly at the core problem… and promise that the future of information management will look very different from its past.

Dan Brown posted a thoughtful follow-up that digs into the distinctions between hierarchy and structure:

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.

Indeed, structure is useful. And instead of one structural option–the folder–we now have derived structure (like search engine indexes and the derived polyhierarchies in iTunes) and user-applied structure (tags, labels, links, playlists). This is not the death of hierarchy; it’s the augmentation of hierarchy.