Editing I-number (section)

{{Short description|Type of Internet identifier}}
{{Lowercase title}}
{{Redirect-distinguish|i number|Imaginary unit}}
{{unreferenced|date=March 2023}}
'''i-numbers''' are a type of [[Internet]] identifier designed to solve the problem of how any [[web resource]] can have a persistent identity that never changes even when the web resource moves or changes its human-friendly name. For example, if a [[web page]] has an i-number, and links to that page use the i-number, then those links will not break even if the page is renamed, the website containing the page is completely reorganized, or the page is moved to another website.

Conceptually, an i-number is similar to an [[IP address]], except i-numbers operate at a much higher level of [[abstraction (computer science)|abstraction]] in Internet addressing architecture. The other key difference is that i-numbers are '''persistent''', i.e., once they are assigned to a resource, they are never reassigned. By contrast, IP addresses are constantly reassigned, e.g., your computer may have a different IP address every time it connects to the Internet.

Technically, an i-number is one form of an [[extensible resource identifier]] (XRI) — an abstract structured identifier standard developed at [[Organization for the Advancement of Structured Information Standards|the Organization for the Advancement of Structured Information Standards]] for sharing resources and data across domains and applications. The other form is called an [[i-name]].

The i-number form of an XRI is designed to serve as an address that does not need to change no matter how often the location of a resource on (or off) the Internet changes. XRIs accomplish this by adding a third layer of abstract addressing over the existing layers: [[Internet Protocol|IP]] numbering (first layer) and [[Domain name system|DNS]] naming (second layer). The notion of a third layer for persistent addressing is not new — [[Uniform Resource Name]]s (URNs) and other [[persistent identifier]] architectures have been developed for this purpose. However, the XRI layer is the first architecture that combines a uniform syntax and resolution protocol for both persistent and reassignable identifiers.

At the [[Extensible Resource Identifier|XRI]] addressing layer, most resources will have ''both'' i-names and i-numbers. These different XRIs that all point to the same resource are called ''synonyms''. I-name synonyms make it easy for humans to discover and address the resource, while i-number synonyms make it easy for machines to maintain a persistent identity for the resource. For example, if a company changes its name, it may register a new i-name and sell its old i-name to another company, however, its i-number can remain the same — and links to the company that use its i-number won't break.

Furthermore, all of these forms of XRI ''synonyms'' can be resolved using the same http- or https-based resolution protocol. The results of XRI resolution are an [[Extensible Markup Language|XML]] document called an XRDS (Extensible Resource Descriptor Sequence). XRDS documents are the basis for the [[Yadis]] identity service discovery protocol that is now part of [[OpenID]].

XRIs are also backwards compatible with the DNS and IP addressing systems, so it is possible for domain names and IP addresses to be used as i-names (or, in rare cases, as i-numbers). Like DNS names, XRIs can also be delegated, i.e., nested multiple levels deep, just like the directory names on a local computer file system. For example, a company can register a top-level (global) i-name and i-number for itself, and then assign second- or lower-level (community) i-names and i-numbers to its divisions, employees, etc.