I-number
I-numbers are one form of an XRI – an abstract identifier designed for sharing resources and data across domains and applications. I-numbers are persistent, machine-friendly XRIs (similar to IP addresses) that are registered once to a resource (person, organization, application, file, digital object, etc.) and never reassigned. This means they can always be used to address a network representation of the resource so as long it remains available somewhere on the network.
One problem XRIs are designed to solve is persistent addressing – how to maintain an address that does not need to change no matter how often the contact data for a person or organization changes. XRIs accomplish this by adding a new layer of abstract addressing over the existing IP numbering and DNS naming layers used on the Internet today. Such an abstraction layer is not new — URNs (Uniform Resource Names) and other persistent identifier architectures do the same thing. What's unique about the XRI layer is that it offers a uniform syntax and resolution protocol for two types of abstract identifiers that mirror the two layers below it (DNS domain names and Internet IP numbers). These are:
- I-names – human-friendly identifiers that resemble domain names but are even simpler and easier to use. Though typically long-lived, i-names may, like domain names, be transferred or reassigned to another resource by their owner. For example, a company that changes its corporate name could sell its old i-name to another company, while both companies could retain their original i-number. However what most differentiates i-names from domain names is that they have paired (synonymous)...
- I-numbers – machine-friendly identifiers (similar to IP addresses) that are registered to a resource (person, organization, application, file, digital object, etc.) and never reassigned. This means an i-number can always be used to address a network representation of the resource as long it remains available somewhere on the network. I-numbers, like IP addresses, are designed to be very efficient for network routers to process and resolve.
XRI syntax also allows i-names and i-numbers to be combined within the same XRI. So effectively the XRI layer supports paired i-name/i-number synonyms for resources – one that reflects real-world semantics and can change over time, and one that reflects the persistent identity of a resource no matter how often its attributes (including its i-names) may change. And the same HTTP-based XRI resolution protocol can be used to resolve either an i-name or an i-number (or any combination of the two in the same XRI).
XRIs are backwards compatible with the DNS and IP addressing systems, so it is possible for domain names and IP addresses to 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 for itself and then assign second- or lower-level (community) i-names to its divisions, employees, etc.
I-names are the other form of XRIs that serve a different purpurse – to be the simplest, most human-friendly identifiers possible. Although intended to be very long-lived, an i-name can be reassigned the same way a domain name can be reassigned. In most cases an i-name is just an easy way to reference an unchanging i-number, the same way a domain name is an easy way to reference an IP address.
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