XRD – Extensible Resource Descriptor
XRD is a simple generic format for describing resources. Resource descriptor documents provide machine-readable information about resources (resource metadata) for the purpose of promoting interoperability, and assist in interacting with unknown resources that support known interfaces.
For example, a web page about an upcoming meeting can provide in its descriptor document the location of the meeting organizer’s free/busy information to potentially negotiate a different time. The descriptor for a social network profile page can identify the location of the user’s address book as well as accounts on other sites. A web service implementing an API protocol can advertise which of the protocol’s optional components are supported.
XRD 1.0 was published on November 1st, 2010 as an OASIS Standard.