Roy says[1] that to be truly RESTful, your resources (documents) need to be linked between each other, just like HTML pages. There are no definite standards yet (that I'm aware of), but JSON HAL[1] seems to be on the IETF standards track to be the one solution we settle on (just like we "settled on" <a href> in HTML). See also [3] for a broader overview on links in JSON and [4] for more information on resource linking and stuff in general.