XDI (short for "eXtensible Data Interchange") is a semantic data interchange format and protocol under development by the OASIS XDI Technical Committee. The name comes from the addressable graph model XDI uses: every node in the XDI graph is its own RDF that is uniquely addressable.
The main features of XDI are: the ability to link and nest RDF graphs to provide context; full addressability of all nodes in the graph at any level of context; representation of XDI operations as graph statements so authorization can be built into the graph (a feature called XDI link contracts); standard serialization formats including JSON and XML; and a simple ontology language for defining shared semantics using XDI dictionary services.
XDI graphs can be serialized in a number of formats, including XML and JSON. Since XDI documents are already fully structured, XML adds very little value, so JSON is the preferred serialization format. The XDI protocol can be bound to multiple transport protocols. The XDI TC is defining bindings to HTTP and HTTPS, however it is also exploring bindings to XMPP and potentially directly to TCP/IP.
XDI provides a standardized portable authorization format called XDI link contracts. Link contracts are themselves XDI documents (which may be contained in other XDI documents) that enable control over the authority, security, privacy, and rights of shared data to be expressed in a standard machine-readable format and understood by any XDI endpoint.
This approach to a globally distributed data sharing network models the real-world mechanism of social contracts and legal contracts that bind civilized people and organizations in the real world today. Thus XDI can be a key enabler of the Social Web. It has also been cited as a mechanism to support a new legal concept, Virtual Rights, which are based on a new legal entity, the "virtual identity", and a new fundamental right: "to have or not to have virtual identities".
- OASIS XDI Technical Committee
- OASIS XDI TC wiki page with links to documents explaining the XDI graph model
- JSON serialization format
- XDI reference implementation in Java Site has live utilities for experimenting directly with XDI