More on Handles and Naming Authorities

Any form of Uniform Resource Name (URN) has three properties:

1. Location independence -- not tied to a particular computer
2. Persistence -- long-term validity
3. Global uniqueness

URN:hdl: naming authority / name

• The naming authority is a registered body. Top-level naming authorities are registered with the global handle server at CNRI. The Library is registered with the global handle server as "loc." Naming authorities can delegate naming privileges by creating sub-authorities; a sub-authority identifier begins with the name of the parent authority followed by a period. For example, The Library can create sub-authorities "loc.pp" and "loc.mbrs."

  Each naming authority is associated with a home handle server. After an initial phase, the Library will have a local handle server under its own control.

• The name is any string assigned by the naming authority. Upper and lower case letters are equivalent. Names are not limited in length, and should not include spaces. To avoid problems that might be created by future operating systems making special use of certain characters, names should probably be limited to alphanumeric characters, supplemented by punctuation characters that are already so commonly used in file names that special uses are unlikely [such as - / . ( ) : and _]. In particular, # and ? should not be used.

  The name portion of the handle has no meaning to the handle server; names can be generated by any conventions that guarantee uniqueness within the naming authority. The general form for handles for items in NDLP collections will consist of a collection or aggregate identifier followed by an identifier for the item.

• Spaces were added to the handle pattern above for legibility. Handles should not contain spaces.

Handles are independent of location

Today's WWW browsers use Uniform Resource Locators which point to files on particular computers. A browser (or any other computer program) that supports URNs will present a location-independent URN to a URN server for resolution into a URL or some other form of locator. CNRI has developed software for a handle server, which is being incorporated into some prototype digital libraries, including a prototype repository for American Memory. When a resource is moved, its record in the handle server is modified. Users of the handle will be unaware of the move. Links to the handle will automatically access the resource from its new location.

Handles are persistent

In comparison with some other candidate schemes for Uniform Resource Names, the CNRI system emphasizes persistence. There is no formal relationship between the scheme's naming authorities and existing network-related names such as Internet domain names, which may change if two publishers merge. Once an item has been named by an authority, its handle can be permanent. The naming authority can move its operations across the country or round the world without a need to alter handles. If an authority goes out of business and ceases to create new handles, the handles it had registered can remain in the system.

Handles are unique

Whenever a naming authority creates a new handle, the handle is checked for uniqueness. The CNRI handle system will allow for reservation of handles in advance.

Continue through this section on the Handle Server:

• A Global System of Handle Servers

Related reading from outside the Library of Congress:

Key Concepts in the Architecture of the Digital Library, William Y. Arms, D-Lib Magazine, July 1995. (hdl:cnri.dlib/july95-arms.html).
[At http://www.dlib.org/dlib/July95/07arms.html].

In this article, based on a presentation at the April 1995 meeting of the Coalition of Networked Information (CNI), Bill Arms of CNRI introduces the handle-server and repository in simple terms and diagrams.

The Handle System: Version 3.0, an Overview.
[At http://www.handle.net/docs/overview.html].

This is a revised edition of the content of the June 1995 Internet Draft by William Arms and David Ely, the original paper proposing the CNRI Handle Server System as a scheme for Uniform Resource Names.

CNRI's web pages for Handles and the Handle System.
[At http://www.handle.net/ ].

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