My latest column is up, Constructing or Traversing URIs?.

"REST is defined by four interface constraints: identification of resources; manipulation of resources through representations; self-descriptive messages; and, hypermedia as the engine of application state." [Roy Fielding]

Of the four interface constraints of REST, the last one, 'hypermedia as the engine of application state', is the least utilitzed. This article builds the concept from the ground up, and then applies it to the design of our Bookmark Web Service.