In part two of his series (part one is here) on building RESTful interfaces, Satish Gopal talks about things like hypermedia and HATEOAS.

This is part 2 of "Building RESTful services". In Part 1 we talked about Level 1 and Level 2 of the Richardson Maturity Model. [...] Now imagine if you had to [find the URI] for every single website, each having a different kind of document in a different custom format. The internet would certainly not be what it is today. Yet a majority of the APIs built today make us do this. This is where the hypermedia concept comes in.

He describes the concepts behind hypermedia, giving examples of how this sort of data can be included in your API's responses. To illustrate, he includes some "link" information that then points to other data for things like "moreInfo" and "reviews" in his Book example. He also describes HATEOAS (Hypermedia As The Engine Of Application State) showing how to use this "link" information to make it simpler for the end user/application to navigate around between data sources in the application.