[semantic navigation offers] the ability to explore and choose perspectives of view based on knowledge of the semantically-structured information.Back in 1994, the Web was only starting to reach a broad audience. The authors cite two examples of social navigation: personal home pages, where people listed sites they found interesting, and collaborative filtering (specifically, the Information Tapestry project at Xerox PARC).
In social navigation, movement from one item to another is provoked as an artifact of the activity of another or a group of others.
Today, a decade and a half later, the web has scaled by several orders of magnitude, search engines have largely obviated the listing of interesting sites on personal home pages, and collaborative filtering, while still going strong as a social influence on user experience, hardly feels like navigation. It does seem that the term "social navigation" deserves an update.
Following Dourish and Chalmers, let us define social navigation as the ability to explore and choose perspectives of view based on social information. Importantly, social navigation is user-controlled navigation just like semantic navigation--only that the user is navigation by changing the social lens on the information rather than specifying semantic constraints.
One example of social navigation is the ratings information at the Internet Movie Database (IMDB). For example, we can see from the ratings for Live Free or Die Hard that the movie appealed most to males under 18.
Fandango (an Endeca customer) takes this concept a step further, offering users faceted navigation of the space of movie reviews, where facets include age, gender, whether or not the reviewer has children, and whether the reviewer lives near the user.
More sophisticated interfaces will intermingle semantic and social navigation. Here is a screen shot from a prototype some of my colleagues put together and demonstrated at HCIR '07: