UPDATE: I updated this diagram in 2009 for the second edition of Designing for Interaction that addresses some of the shortcomings I note below. The diagram now looks like this (click for larger image):
Like almost nothing I’ve done, a model that I put in my first book Designing for Interaction showing the overlapping disciplines of user experience/experience design has been referenced repeatedly in various places. The problem is I was never very happy with the diagram. For one thing, it’s missing architecture in there, which is becoming increasing important. So I redrew it:
It’s still not perfect: it’s missing Sound Design and Ergonomics/Human Factors, and the way the circles had to overlap downplays Visual Design. But I like it better, as it shows some of the products of the overlapping disciplines, and also includes content in there too. HCI is partially out of the circle because of its different (non-design) traditions and methodologies, and also because of its focus on pure research. Industrial design (and, in truth, architecture should do this too), pokes out of the circle because it has involvement in areas that do not directly involve the user, such as manufacturing (or in the case of architecture, building) specifications.
This diagram also begs the question: what is user experience design by itself, those areas that aren’t filled up with other bubbles? I tried to answer some of that in an earlier post, but the short answer is: not much, aside from coordination between the various disciplines, or what used to be called creative direction. It’s about the joining of the different disciplines, and not particularly a discipline in and of itself. While the best designers have an awareness of the disciplines that surround and overlap theirs, to be considered an experience designer would necessarily require management and coordination between the disciplines to ensure holistic products. This is an essential skill for making the best products, of course, but I would guess this is often a temporary role that designers move into during key points in the design process from a starting point of one of the other disciplines. Without the “raw materials” of the disciplines that make up UX, UX would be empty indeed.