A uniform resource identifier (URI) is a uniform resource locator（定位器，探测器） (URL), uniform resource name (URN), or both.
In computing, a uniform resource name (URN) is the historical name for a uniform resource identifier (URI) that uses the urn scheme. A URI is a string of characters used to identify a name of a web resource. Such identification enables interaction with representations of the web resource over a network, typically the World Wide Web, using specific protocols.
Defined in 1997 in RFC 2141, URNs were intended to serve as persistent, location-independent identifiers, allowing the simple mapping of namespaces into a single URN namespace.[1] The existence of such a URI does not imply availability of the identified resource, but such URIs are required to remain globally unique and persistent, even when the resource ceases to exist or becomes unavailable.[2]
Since RFC 3986[2] in 2005, the use of the term has been deprecated in favor of the less-restrictive "URI", a view proposed by a joint working group between the World Wide Web Consortium (W3C) and Internet Engineering Task Force (IETF).[3] Both URNs and uniform resource locators (URLs) are URIs, and a particular URI may be a name and a locator at the same time.
URNs were originally intended in the 1990s to be part of a three-part information architecture for the Internet, along with URLs and uniform resource characteristics (URCs), ametadata framework. However, URCs never progressed past the conceptual stage,[3] and other technologies such as the Resource Description Framework later took their place.