XRI (eXtensible Resource Identifier) 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 XRIs is to provide a universal format for identifiers that are domain-, location-, application-, and transport-independent, so they can be shared across any number of domains, directories, and interaction protocols. A Uniform Resource Identifier (URI), is an Internet protocol element consisting of a short string of characters that conform to a certain syntax. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... The Organization for the Advancement of Structured Information Standards (OASIS) is a global consortium that drives the development, convergence and adoption of e-business and web service standards. ...

Background & Motivations

URIs -- the address of every resource on the Web -- are the most successful identifiers in history. However the growth of the Web has led to new requirements for resource identifiers that are not easily met by standard URI syntax. One of these key requirements -- internationalization -- was ultimately met by the W3C and IETF by developing a new form of URI called an Internationalized Resource Identifier (IRI). The IRI specifications built on the URI standard by extending the character set to support the full range of Unicode characters. A Uniform Resource Identifier (URI), is an Internet protocol element consisting of a short string of characters that conform to a certain syntax. ... The World Wide Web Consortium (W3C) is a consortium that produces standards—recommendations, as they call them—for the World Wide Web. ... The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... Unicode is an international standard whose goal is to provide the means by which text of all forms and languages can be encoded for use by computers. ...

With the growth of XML, Web services, and other ways of adapting the Web to automated, machine-to-machine communications, another set of requirements has emerged. These are the requirements to be able to identify a resource independent of a specific physical network path, location, or protocol because you need to: The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. ... A web service is a collection of protocols and standards used for exchanging data between applications. ...

• Create structured identifiers with self-describing "tags" that can be understood across domains the same way XML documents provide a self-describing, domain-independent data format.
• Maintain a persistent link to the resource regardless of whether its network location changes.
• Delegate identifier management not just in the authority segment (the first segment following the "xxx://" scheme name) but anywhere in the identifier path.
• Map identifiers used to identify a resource in one domain to other "synonyms" used to identify the same resource in the same domain, or in other domains.

By early 2003, these requirements led to the establishment of a new technical committee at OASIS whose goal was to create a new type of identifier that built on top of the IRI specification the same way the IRI specification built on top of the URI specification. The XRI TC was also charged with creating an optional resolution protocol based on HTTP and simple XML documents called Extensible Resource Descriptors (XRDs). The Organization for the Advancement of Structured Information Standards (OASIS) is a global consortium that drives the development, convergence and adoption of e-business and web service standards. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... A Uniform Resource Identifier (URI), is an Internet protocol element consisting of a short string of characters that conform to a certain syntax. ...

Features

• URI- and IRI-compatibility — XRIs can be used wherever URIs or IRIs are called for.
• Cross-references — An XRI can contain another XRI (or a URI), to any level of nesting. This enables the construction of structured, "tagged" identifiers that enable identifier sharing across domains the same way XML enables data sharing across domains.
• Global context symbols — These are single-character symbols (=, @, +, $, or !) that provide a simple, human-friendly way to indicate the global context of an i-name or i-number. These are not required, but may be used within communities of interest that agree on their meaning and how they are resolved.
• Peer-to-peer addressing — XRI syntax supports the ability for any two network nodes to assign each other XRIs and perform cross-resolution. That is, a top-level namespace authority can be referred to by names assigned by other parties. This aids in federating namespaces between organizations or communities of interest.
• Decentralization — XRIs can be rooted in either centralized addressing systems (e.g., IP addresses or DNS domain names) or private/decentralized root authorities.
• Delegation — Namespaces can be delegated to other namespace authorities.
• Federation — Namespaces defined separately at any level can be joined together in a hierarchical or polyarchical fashion, and made visible and resolvable.
• Persistence — The ability to express the intent that parts (or all) of an XRI are permanent identifiers that will never be reassigned.
• Human-friendly and machine-friendly formats — XRI provides syntax both for identifiers that can be structured and parsed by humans easily, and those that are optimized for machine structuring/parsing.
• Simple, extensible resolution — XRI offers a lightweight resolution scheme using HTTP and simple XML documents.
• Trusted resolution — the XRI resolution protocol includes a trusted version that uses SAML assertions.
• Multiple resolution options — XRI resolution can be independent of DNS.
• Fully internationalizable, leveraging Unicode and IRI specifications.
• Transport independent — XRIs are not bound to any specific transport protocols or mechanism.

A Uniform Resource Identifier (URI), is an Internet protocol element consisting of a short string of characters that conform to a certain syntax. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ... I-name - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... I-numbers are one form of an XRI - an abstract identifier designed for sharing resources and data across domains and applications. ... A peer-to-peer (or P2P) computer network is a network that relies on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively few servers. ... Security Assertion Markup Language (SAML) is an XML standard for exchanging authentication and authorization data between security domains, that is, between an identity provider and a service provider. ... Internationalization and localization are means of adapting products such as publications or software for non-native environments, especially other nations and cultures. ... Unicode is an international standard whose goal is to provide the means by which text of all forms and languages can be encoded for use by computers. ... The introduction of this article does not provide enough context for readers unfamiliar with the subject. ...

Why not just use HTTP URIs?

The XRI Technical Commitee is composing a list of answers to this frequently asked question. Following is a summary of the key points.

• What does HTTP URI identify? Permathread at W3C TAG and elsewhere. The TC wanted to avoid this confusion. (Transport independence requirement, Requirement to be able to identify anything)
• HTTP URIs don't have the delegation model needed. (Delegation requirement)
• HTTP URIs don't define a clear way to get at metadata (as opposed to data) about a identified resource. A single XRI is intended to be used different ways and in ways we don't know yet. Extensibility of metadata is important. DNS is very limited in terms of what it can describe (even with NAPTR and DDDS). (Extensibility requirement, Transport-independence requirement)
• HTTP URIs typically use DNS and DNS and doesn't support the trusted delegation model the TC has identified in its requirements. Resolution has to start with a trusted root and that root should be defined by the community of users. Using IP addresses instead of DNS is even worse because the delegation is limited by network topology. (Trusted resolution requirement, Delegation requirement)
• Some folks don't trust DNS at all - too easy to perform DoS, for example. Pharming attacks, etc. (Trusted resolution requirement)
• HTTP URIs don't support use of other identifiers in the delegation path - each part of the path is limited in its syntax. (Extensibility requirement, Cross references requirement).
• HTTP URIs require use of IP Addresses or DNS names, both of which are managed in ways which may not work well with the intent behind using an XRI (ie. a DNS name may go away due to legal issues, etc, IP Addresses change). (Persistence requirement)
• There's no way to discover what capabilities the resource associated with an HTTP URI have (in terms of network interaction) - all you know about is HTTP verbs (and then, unless you have a functioning OPTIONS command, you have to guess). There's no defined way to get at metadata about a resource separately from interacting with it.

http is the most popular URI scheme used on the World Wide Web. ... Technical Architecture Group, a body of W3C. (from TAG charter) Currently (August 2005), Tim Berners-Lee is the Chair of the TAG. Other members are: Dan Connolly (W3C) Roy Fielding (Day Software) Noah Mendelsohn (IBM) David Orchard (BEA) Vincent Quint (INRIA) Ed Rice (HP) Henry Thompson (University of Edinburgh) Norm... Delegation is handing a task over to a subordinate. ... Metadata (Greek: meta-+ Latin: data information), literally data about data, is information that describes another set of data. ... The Domain Name System (DNS) is a system that stores information associated with domain names in a distributed database on networks, such as the Internet. ... NAPTR stands for Naming Authority Pointer and is a newer type of DNS record that supports regular expression based rewriting. ... Defined in RFC 3401, RFC 3402, RFC 3403, RFC 3404, and RFC 3405. ... The acronym DOS stands for disk operating system, an operating system component for computers that provides the abstraction of a file system resident on hard disk or floppy disk secondary storage. ... Pharming is the exploitation of a vulnerability in the DNS server software that allows a cracker to acquire the Domain name for a site, and to redirect that websites traffic to another web site. ... An IP address is a unique number that devices implementing the Internet Protocol use in order to identify each other on a network. ...

Applications

Examples of applications being developed using XRI infrastructure include:

• I-name and I-number addressing services.
• I-tags for structured tagging.
• XDI trusted data sharing protocol under development by the OASIS XDI Technical Committee.

I-name - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... I-numbers are one form of an XRI - an abstract identifier designed for sharing resources and data across domains and applications. ... XDI (XRI Data Interchange) is a generalized, extensible service for sharing, linking, and synchronizing data over the Internet and other data networks using XML documents and XRIs (Extensible Resource Identifiers). ... Oasis in the Libyan part of the Sahara In geography, an oasis is an isolated area of vegetation in a desert, typically surrounding a spring or similar water source. ...

Examples

(Note that none of these show the prefix "xri://", which is optional in XRIs when they are not in URI normal form.)

Example XRIs composed entirely of reassignable segments:

 =Mary.Jones @Jones.and.Company +phone.number +phone.number/(+area.code) =Mary.Jones/(+phone.number) @Jones.and.Company/(+phone.number) @Jones.and.Company/((+phone.number)/(+area.code)) 

Example XRIs composed entirely of persistent segments:

 !!1002!A7C5 !!1002!A7C5/!D90F.88 

Example of XRIs with mixes of persistent and reassignable segments (XRI allows any combination of the two):

 !!1002!A745/(+phone.number) @Jones.and.Company/!D90F.88/(+area.code) 

See also

• I-names
• I-numbers
• XDI
• Dataweb
• Social Web
• Identity Centric Architecture
• Project Xanadu

I-name - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... I-numbers are one form of an XRI - an abstract identifier designed for sharing resources and data across domains and applications. ... XDI (XRI Data Interchange) is a generalized, extensible service for sharing, linking, and synchronizing data over the Internet and other data networks using XML documents and XRIs (Extensible Resource Identifiers). ... The Dataweb is a new approach to distributed data sharing that applies the proven principles of the World Wide Web to the sharing and linking of machine-readable data across domains and applications. ... The Social Web refers to an open global distributed data sharing network similar to todays World Wide Web, except instead of linking documents, the Social Web will link people, organizations, and concepts. ... Identity Centric Architecture is the discipline of designing systems that put the concepts of secure, distributed, open and owner controlled digital identity at their center. ... Project Xanadu was founded by Ted Nelson in 1960 as the original hypertext project. ...

External links

• OASIS XRI Technical Committee
• OASIS XDI Technical Committee
• W3C Internationalized Resource Identifier (IRI)
• XDI.ORG
• Documents:
  • XRI Syntax 2.0 (final Committee Specification)
  • XRI Resolution 2.0 (Committe Draft -- still in progress)
  • XRI Metadata 2.0 (Committee Draft -- still in progress)
  • XRI Introduction 2.0 (Working Draft
  • XRI Requirements and Glossary 1.0