and easily discoverable, whereas unidirectional identifiers are intended to be private and used only in the context of a specific identity relationship. Identifiers may also be classified as resolvable or non-resolvable. Resolvable identifiers, such as a domain name or email address, may be easily dereferenced into the entity they represent, or some current state data providing relevant attributes of that entity. Non-resolvable identifiers, such as a person's real name, or the name of a subject or topic, can be compared for equivalence but are not otherwise machine-understandable. There are many different schemes and formats for digital identifiers. Uniform Resource Identifier (URI) and the internationalized version Internationalized Resource Identifier (IRI) are the standard for identifiers for websites on the World Wide Web. OpenID and Light-weight Identity are two web authentication protocols that use standard HTTP URIs (often called URLs). A Uniform Resource Name is a persistent, location-independent identifier assigned within the defined namespace. Digital Object Architecture Digital Object Architecture is a means of managing digital information in a network environment. In Digital Object Architecture, a digital object has a machine and platform independent structure that allows it to be identified, accessed and protected, as appropriate. A digital object may incorporate not only informational elements, i.e., a digitized version of a paper, movie or sound recording, but also the unique identifier of the digital object and other metadata about the digital object. The metadata may include restrictions on access to digital objects, notices of ownership, and identifiers for licensing agreements, if appropriate. Handle System The Handle System is a general purpose distributed information system that provides efficient, extensible, and secure identifier and resolution services for use on networks such as the internet. It includes an open set of protocols, a namespace, and a reference implementation of the protocols. The protocols enable a distributed computer system to store identifiers, known as handles, of arbitrary resources and resolve those handles into the information necessary to locate, access, contact, authenticate, or otherwise make use of the resources. This information can be changed as needed to reflect the current state of the identified resource without changing its identifier, thus allowing the name of the item to persist over changes of location and other related state information. The original version of the Handle System technology was developed with support from the Defense Advanced Research Projects Agency. Extensible Resource Identifiers A new OASIS standard for abstract, structured identifiers,