Uniform Resource Identifier

Term used by the W3C consortium for labels used for web content. URIs include both Uniform Resource Locators (example: http://subdomain.domain/name1/name2...) and Uniform Resource Names (example: urn:domain:subdomain:name1:name2...).

Universally Unique Identifiers (UUIDs)

A Universally Unique Identifier is a code (sequence of characters or binary value) which is generated on request, and is expected to not be duplicated across all computer applications. It is an important capability when trying to refer to objects uniquely, that is, by a unique reference number.

This important topic is discussed in many places, but a reasonable overview with many references is at Wikipedia.

Architecture of the World Wide Web (Vol 1)

This document by W3C (the World Wide Web Consortium) presents the architecture of the World Wide Web.

It extensively describes the purpose and use of Universal Resource Identifiers. It describes their relationship to the resources they identify, and how URIs and other web resources are resolved by the agents (servers and clients) to provide the desired content.

This document includes many best practices for the use of URIs.

Identifying Web Resources

This discussion on the SeeGRID pages provides considerable context for the question of web identifiers.

IANA Namespaces for URNs

This IANA registry provides links to the document that describes each URN scheme.

OGC Best Practices for URNs

a best practice document that describes a standard mechanism for using URNs to reference various abstract concepts and resources, especially those relating to coordinate reference systems (e.g. datums, ellipsoids, prime meridians, etc). The URNs follow the format "urn:ogc:def:crs:EPSG:6.3:26986" (for a CRS defined in the EPSG codespace, in this example)

URI Generic Syntax (IETF)

Original Request for Comment document of IETF describing URIs.

Includes the following: ...although many URI schemes (e.g. URLs) are named after protocols, this does not imply that use of these URIs will result in access to the resource via the named protocol. URIs are often used simply for the sake of identification...

Persistent Uniform Resource Locators (PURL)

A PURL provides a reference to an intermediate resolution service. The PURL resolution service associates the PURL with the actual URL and returns that URL to the client.

A PURL has three parts: (1) a protocol, (2) a resolver address, and (3) a name. A PURL looks like any of the following:

The Handle System Digital Object Architecture

This system provides an architecture, upon which other systems can be built, for handling and referencing digital objects. It is a fee-based service to offset the costs of its operation.

Archival Resource Keys

This persistent digital object identifer technology is currently being implemented and tested by the California Digital Library (CDL) for collections that it manages.

The ARK identifier is a specially constructed, globally unique, actionable URL designed to be without semantic association to the related item. Each ARK links end-users to three things:

Term Resolution Discussion

This discussion on the SeeGRID pages provides a number of options to consider when trying to define resolvable unique terms.

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