overview
on the web
Dublin Core
RDF
PICS
PURLs
URNs
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URNs
As the web evolves some experts are calling for Uniform Resource Name (URNs)
to complement - or replace - Uniform Resource Locators (URLs) in
identifying and thereby retrieving online documents.
URNs would, it's
claimed, provide a persistent and unique
identifier for digital resources - a more powerful version of the ISBNs
used by librarian and publishers to identify books.
URLs
Finding information on the web is based on URLs - an address for each
document with a format that's similar to the URL for this page: connectingguide10.htm
URLs identify documents according to their location. This document, for
example is located in the identification folder of the briefings
component of the Caslon domain within the dot com domain space.
URLs are familiar to most users of the web, who take them for granted
as a mechanism for identifying online documents and describing their
location for future retrieval. However, they have been criticised by some
as unsatisfactory.
Critics note that each URL simply points to the current
location of a document, rather than uniquely identifying it independent of
its location in cyberspace. If a resource is moved to a new location
(renamed, placed in a new folder on the same site, moved to a new site),
the URL is no longer useful because it points to a location that no longer
exists. It's not unique and it's not persistent.
Librarians, publishers and proponents of global electronic copyright
management systems (ECMS)
have thus argued that a persistent and unique identifier would be specific
to a particular digital resource. Their vision is that identification
independent of location would facilitate access to the document regardless
of its location, as long as it still existed on the Internet, and underpin
rights tracking systems.
concept
Proposals for a Uniform Resource Name (URN) scheme have two parts.
Each document would be marked with a standard, persistent and unique
identifier as part of its metadata.
So that users could link from the URN to the specific URL, a 'resolver service'
- essentially a global automated directory - would be required.
The expectation is that URNs would include a Namespace Identifier
(NID) code and a Namespace Specific String (NSS). The NID code would flag the
identification system being used and facilitate
interpretation of the NSS, a unique code identifying the individual document.
Where would the NID and NSS come from? The vision is that the international ISBN and ISSN agencies
- described in our ECMS
profile - would use the existing International Standard Book Number (ISBN)
and International Standard Serial Number (ISSN) as the NIDs. Various
national libraries, including Australia's NLA, are considering URNs based on National
Bibliography Numbers (NBN), with 'NBN' as the Namespace Identifier and the
existing
NBN used as the NSS.
What would it look like? There's a detailed
explanation of an NBN system in the Nordic
Metadata Project's URN User Guide (UUGuide).
coming soon to a desktop near you?
Advocates for the URN - primarily drawn within the library sector and
associated information technology researchers - have claimed that "the Uniform Resource Name (URN) may eventually be the
internet standard for identifying and
finding electronic resources".
At this stage that claim appears
overambitious. It assumes achievement of a network architecture - in
particular the resolver service - that is still taking shape. Work by the Internet
Engineering Task Force's (IETF) Uniform
Resource Names Working Group (URNWG)
continues.
Just as importantly, while it's easy for
particular sectors to mandate standards, getting the commitment of the
people who create web pages is another matter. The experience of the
library sector in promulgating the Dublin Core (DC)
metadata standard is a good example.
DC has not broken outside the walls
of the curatorial ghetto and thus is found on much less than 1% of the
web. It is unclear whether businesses, individuals, non-profit groups and
even many academic institutions can be persuaded to adopt URN,
particularly since reported noted in our
Metrics guide suggest that the half life of pages on the web is less than two
years.
The publisher-oriented Digital Object Identifier
(DOI) scheme, perhaps the most advanced
ECMS project, is less ambitious, using the competing Handle
system to allocate a unique digital identifier to
commercial digital publications.
As an "interim measure" some
figures are promoting the Persistent Uniform Resource Locator (PURL),
in which the identifier points to a resolution service instead of the
actual location of the digital resource. The resolution service then
redirects the user to the appropriate URL, serving as another link to the
current location of the particular document. When that document's location
changes, it would only be necessary to update the PURL resolver service
for users to find it with the same PURL.
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