The impact of digital technology—from the Web to mobile phones to the silicon in your toaster—has meant a proliferation of terms for the work people do to define digital products and services. People talk about "customer experience," "user-centered design," and so forth. This talk can confuse even people who do that work for a living, as you often find different people using different terms to mean the same thing—or using the same term to mean very different things!

Many people say that this reflects a breakdown of disciplinary distinctions in designing for the new world of the digital. "It's all just design." I disagree. I see a few major types of problems in the digital world, and I believe that each of these has its own set of tools and methods that work well to solve that type of problem.

Two of these types of problems lurk behind the terms "information architecture" and "interaction design." As I said, we live in times with slippery terms, so I want to admit that I'm using these expressions in a way that may differ from the way you or your colleagues do. Though I have some good reasons for thinking that I use these terms in the most useful and appropriate way, I want less to advocate for certain language than to make clear something about two different kinds of problems that emerge in designing for the Web.

To understand why the distinction between these problems can become obscured, it helps to look back over the history of Web design. Early in the growth of the Web, many graphic designers with backgrounds in print media migrated into Web design. They discovered that the specifics of good graphic design in print don't always work so well on the Web, and creating good Web sites required some new techniques. But graphic design for the Web was still graphic design.

On the other hand, as Web sites grew larger, with more and more content, Web designers came to realize that creating effective Web sites requires solutions to some problems very different from those addressed by graphic design. Not only do individual pages need to look appealing and readable, but you need to organize and label links so that people can find the content in a large site. We now call those "information architecture" (IA) problems. The methods of graphic design don't help with IA, and for a time Web developers struggled with IA problems, even having trouble recognizing that these problems even existed. But at this point Web development organizations understand the distinction between graphic design and IA, and recognize IA as its own distinct discipline with fairly-well understood methods and techniques.

Because the culture of Web design remains strongly rooted in graphic design, many conceive of IA as "all Web design that isn't graphic design." But that misses another important distinction.

Just as the growth of Web sites created problems in organizing content, giving rise to the discipline of IA, so too the appearance of Web sites generated by complicated software generating unique pages that people use as tools, calling for a discipline I prefer to call "interaction design." (IxD)

Let's unpack that distinction.

IA means defining information structures to answer the question "how does a user find the information they want?" Thus navigation links for a big corporate Web site reflect IA: where can I find directions to the company's main headquarters? When you talk about content, page hierarchy, and taxonomy, you probably have an IA problem.

On the other hand, IxD means defining system behaviors to answer the question "how does a user take the action they want?" Thus the pulldowns, buttons, and checkboxes in a Web email application reflect IxD: what must I do to reply to the sender of this email? When you talk about action, controls, and dynamic elements, you probably have in IxD problem. Some problems include both components: consider how Amazon includes both large amounts of static content and some very complex dynamic behaviors.

It turns out that the techniques for doing these two things differ dramatically, at least as much as they differ from the techniques of graphic design. IA calls for exercises like card sorts, usability testing for category labels, hierarchical structure diagramming, and so forth. IxD calls for exercises like workflow analysis, usage scenarios, wireframed walkthroughs, and so on. The work done, and the skills needed to do it, differ considerably between the two. Just as few people can fully master the skills of both graphic design and IA, few people will master the skills of both IA and IxD. It serves both organizations and practitioners for people to specialize.

So when thinking about a new Web site, first ask what kind of problem you have, to make sure that you bring the right people—and the right tools—for the job.