Tuesday, December 27, 2005

A Mobile User Interface Paradigm

The iPod has popularized a user interface style: side scrolling navigation of a hierarchy. But is it more than a style? Does the iPod point to a paradigm for small-screen user interface the way that Macintosh popularized and formalized (through Apple’s fascistic insistence on user interface standards) the desktop metaphor?

The iPod interface is not original, and the USPTO has thus far ruled it isn’t novel. Creative Labs and Microsoft both hold related patents, and a hierarchical user interface is fundamentally unoriginal. But, as with Macintosh, taking a good idea more seriously than one’s competitors has given Apple the leading position in establishing the iPod user interface as the best example of a new paradigm.

That new paradigm can be summed up as “node by node visualization of taxonomy browsing.” Evidently I won’t go down in history as coining a new moniker as succinct as “desktop metaphor,” but the concept of taxonomy browsing on a small screen deserves almost as much exposition as the desktop metaphor in order to explore what it can do for small-device user interface.

On the iPod, the taxonomy is composed by iTunes and downloaded into the iPod. The iPod user browses the taxonomy node by node. That is, only one node of one taxonomy is viewable at any one time. That sounds rather unattractive, for a couple reasons: First, it comes off as limiting. Who would not want to see more information if they could? Second, “hierarchy” has become a bad word. Search-based file browsers on PCs are happily burying one of the worst user interface ideas ever created in computing – the file hierarchy.

And yet, the iPod is clearly a brilliant user interface. How does Apple turn limitations and what seems to be an out-of-style idea like hierarchy into user interface gold? With two broad approaches: First, accept limitations. Do not strain to deny them. Second, work to create the best user interface within the limitations. Much the same could be said about the difference between Lisa and Macintosh. Lisa did not accept limitations. Consequently, it was slow, and it highlighted the limitations of the Lisa platform. Macintosh accepted tighter hardware limitations than Lisa, and did what was needed to provide an excellent user experience within those limitations. Apple, in the person of Steve Jobs, and institutionally, clearly remembers those lessons.

In the iPod, limitations are ameliorated by the perfect interplay of the physical user interface and the “trail of crumbs” browsing interface. It enables the user to access one branch of a taxonomy so easily that the one-node-at-a-time limitation of the view into the taxonomy is no burden. In fact, compared to more-conventional taxonomy browsing interface of iTunes, it is a model of clarity.

Is this really a paradigm? Is it applicable to domains outside of music taxonomies? With specific examples thin on the ground one has to drill into the paradigm to come up with an answer. Here, I will state that answer in the form of how iPod-like taxonomy browsing fits the model-view-controller architecture for user interfaces: If the model is static, or nearly so, and if the model can be created from some interaction outside the hierarchical view system, such as the iTunes database, or some other database query, and if the results of that query form one or more taxonomies of categories, with nodes of manageable size, then taxonomy browsing iPod-style is a valid paradigm. Speculating on what kinds of applications fit this description, one can think of social networks, heterarchies like semantic networks (such as the CNet semantic network of news stories), and even first party call control interfaces, which I have seen implemented as a menu hierarchy attached to a tray icon.

I think this is enough to define a taxonomy browsing user interface paradigm, and test that node-by-node visualization and trail-of-crumbs forward/backward linking are a good visualization of that paradigm. I did not delve into physical UI and controller design, and it may be that the iPod wheel is key, but I will assert it is not, and that the mobile handset dpad is sufficient (perhaps this will emerge as a single-button versus multi-button mouse theosophical topic).

Now how about some iPod phone rumors!

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