HATEOAS

HATEOAS, an abbreviation for HyperMedia as the Engine of Application State, is a constraint of the ReST application architecture that distinguishes it from most other network application architectures. The principle is that a client interacts with a network application entirely through hypermedia provided dynamically by application servers. A REST client needs no prior knowledge about how to interact with any particular application or server beyond a generic understanding of hypermedia. By contrast, in a service-oriented architecture (SOA), clients and servers interact through a fixed interface shared through documentation or an interface description language (IDL). http://en.wikipedia.org/wiki/HATEOAS

HAL is a simple format that gives a consistent and easy way to hyperlink between resources in your API.