Extensible Resource Identifier

An Extensible Resource Identifier (abbreviated XRI) is a scheme and resolution protocol for abstract identifiers compatible with Uniform Resource Identifiers and Internationalized Resource Identifiers, developed by the XRI Technical Committee at OASIS. The goal of XRI is a standard syntax and discovery format for abstract, structured identifiers that are domain-, location-, application-, and transport-independent, so they can be shared across any number of domains, directories, and .

The XRI 2.0 specifications were rejected by OASIS, a failure attributed to the intervention of the W3C Technical Architecture Group which recommended against using XRIs or taking the XRI specifications forward. The core of the dispute is whether the widely interoperable URIs are capable of fulfilling the role of abstract, structured identifiers, as the TAG believes, but whose limitations the XRI Technical Committee was formed specifically to address.

The designers of XRI believed that, due to the growth of XML, web services, and other ways of adapting the Web to automated, machine-to-machine communications, it was increasingly important to be able to identify a resource independent of any specific physical network path, location, or protocol in order to:

This work led, by early 2003, to the publication of a protocol based on HTTP(S) and simple XML documents called XRDS (Extensible Resource Descriptor Sequence).

An XRI starting with "=" is thought of identifying a person. An XRI starting with "@" identifies a company or organization. A starting "+" indicates a generic concept, subject or topic.

A "*" marks a delegation. For example with "=family*name", "=family" delegates the resolving of its sub-XRI "name" to another resolver. This is analogous to DNS' delegating the subdomain resolution to other nameservers (name.family.de: after resolving de, the nameserver responsible for de delegates to the family nameserver, which delegates to the name nameserver).

XRIs are resolved to XRDS documents using the HTTP(S) protocol in the same way as URLs are resolved to resource records using the DNS protocol. This lookup process can be configured by passing parameters.

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