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Foundation of Library and Information Science

Notes identifying objects on the Internet. URL’s confound in one string several items that should be
separate. They include the method by which a document is accessed (e.g., HTTP), a machine
name and document path (its location), and a document file name which may or may not be
unique (e.g., how many index.html files do you have on your Web site?). URLs are very bad
names because whenever a file is moved, the document is often lost entirely.
A global scheme of unique identifiers is required; one that has persistence beyond the life of the
originating organization and that is not tied to specific locations or processes. These names must
remain valid whenever documents are moved from one location to another, or are migrated
from one storage medium to another.
Three examples of schemes proposed to get around the problem of persistent naming are PURLs,
URNs, and Digital Object Identifiers.
PURLS: PURLs are persistent URLs. They are a scheme developed by OCLC in an attempt to
separate a document name from its location and therefore increase the probability that it
will always be found. PURLs work through a mapping of a unique, never-changing PURL to
an actual URL. If a document moves, the URL is updated, but the PURL stays the same. In
operation, a user requests a document through a PURL, a PURL server looks up the
corresponding URL in a database, and then the URL is used to pass the document to the user.
Because PURLs also confound a name with an access method, like URLs, they are not true
Uniform Resource Name (URN): URNs are a development of the Internet Engineering Task
Force (IETF). A URN is not a naming scheme in itself, but a framework for defining identifiers
(Lynch, 1998). They contain a naming authority identifier (a central authority given the task
of assigning identifiers) and an object identifier (assigned by the central authority). Like
PURLs, URNs must be resolved, through a database or other such system, into actual URLs.
Unlike PURLs, however, a URN can be resolved into more than one URL, such as one for
each of several different formats. There is currently no working URN system.
Digital Object Identifier (DOI) System: DOI is an initiative by the Association of American
Publishers and the (American) Corporation for National Research Initiatives designed to
provide a method by which digital objects can be reliably identified and accessed. The
CNRI Handle system, which underlies DOI, is a system that resolves digital identifiers
into the information required to locate and access a digital object. The main impetus of the
DOI system is to provide publishers with a method by which the intellectual property
right issues associated with their materials can be managed.
The issue of persistent naming raises it head in a coordinated scheme, as well. Persistent names
are an organizational problem, rather than an engineering problem. Technically, a system to
handle names is possible; however, unique identifiers will only persist if some institution takes
responsibility for their management and migration from a current technology to succeeding
generations of technologies. Thus, one goal of a coordinated digital library scheme would be to
identify an institution or institutions that would take charge of issuing, resolving, and migrating
a system of unique names.

10.2.3 Preservation

Another important issue is preservation—keeping digital information available in perpetuity.
In the preservation of digital materials, the real issue is technical obsolescence. Technical
obsolescence in the digital age is like the deterioration of paper in the paper age. Libraries in the
pre-digital era had to worry about climate control and the de-acidification of books, but the
preservation of digital information will mean constantly coming up with new technical solutions.
When considering digital materials, there are three types of “preservation” one can refer to:

The preservation of the storage medium: Tapes, hard drives, and floppy discs have a very
short life span when considered in terms of obsolescence. The data on them can be refreshed;

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