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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 interaction protocols. The XRI 2.0 specifications were rejected by OASIS,〔(Failed OASIS )〕 a failure attributed〔(Time for OASIS XRI TC and W3C TAG to Sit Down Together )〕 to the intervention of the W3C Technical Architecture Group which recommended against using XRIs or taking the XRI specifications forward.〔(TAG recommends against XRI )〕 The core of the dispute is whether the widely interoperable HTTP URIs are capable of fulfilling the role of abstract, structured identifiers, as the TAG believes,〔(URNs, Namespaces and Registries )〕 but whose limitations the XRI Technical Committee was formed specifically to address.〔(Xri Solves Real Problems )〕 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: * Create structured identifiers with self-describing "tags" that can be understood across domains. * 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. 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). == Features == ; URI- and IRI-compatibility : There is a specified way to express XRIs in the form of URIs ; 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. See also: Global context registries.; 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 and peer-to-peer addressing. ; 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- and machine-friendly formats : XRI provides syntax both for identifiers that can be created and understood by humans easily (i-names), and those that are optimized for machine structuring/parsing (i-numbers). ; Simple, extensible resolution : XRI offers a lightweight resolution scheme using HTTP and a simple XML document format called XRDS. ; Trusted resolution : The XRI resolution protocol includes three modes of trusted version: a) HTTPS, b) SAML assertions, and c) both. ; Multiple resolution options : XRI resolution can be independent of DNS. ; Fully internationalizable : Leverage existing Unicode and IRI specifications. ; Transport independent : XRIs are independent of specific transport protocols or mechanisms. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Extensible resource identifier」の詳細全文を読む スポンサード リンク
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