More on Handles and Naming Authorities

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

1. Location independence
2. Persistence -- long-term validity
3. Global uniqueness

hdl: naming authority / name

• The naming authority is a registered body. Top-level naming authorities are registered with the global handle server at CNRI. LC will be registered with the global handle server, probably, but not necessarily, as "loc" to match its Internet domain name of "loc.gov." 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, LC could create sub-authorities "loc.pp" and "loc.mbrs."

  Each naming authority is associated with a primary handle server, which can be the global handle server. After an initial phase, LC 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 _].

  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. For some applications, serial numbers or date-time stamps might be appropriate. For many, a mnemonic structure that will be relatively easy for a human being to remember or transcribe without error would be preferable. In some cases, an appropriate standard may exist or be under consideration. For example, journal publishers creating digital archives might use the standard Serial Item and Contribution Identifier (SICI) which extends the ISSN to identify a particular article in a serial. The general form for handles for items in NDLP collections will probably consist of a collection 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

Like the other URN proposals, the handle scheme satisfies this requirement by introducing an intermediate step in the access process. Today's WWW browsers use Uniform Resource Locators which point to files on particular computers. A browser that supports URNs will present a location-independent URN to a URN server for resolution into a URL or some other form of locator. When a resource is moved, its handle-server record 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.

To provide maximum flexibility during the initial development phase, CNRI has developed its own browser, GRAIL, to recognize and support handles and repositories. In the future, CNRI expects to build plug-in features for other browsers, possibly using JAVA, Sun Microsystems' new system for platform-independent program modules.

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 Internet domain names. 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 under the control of another naming authority.

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
• How the Handle Server Works with the Repository

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: A Technical Overview. William Arms & David Ely, June 23, 1995.
[At http://www.cnri.reston.va.us/home/cstr/handle-overview.html].

This is a reformatting of the content of Internet Draft draft-ietf-uri-urn-handles-00.txt, 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/ ].

CNRI's web pages for GRAIL (version 0.2).
[At http://monty.cnri.reston.va.us/grail-0.2/ ].

GRAIL is a web-browser developed by CNRI to be easily extensible and easily converted ("ported") to other computing platforms. By having their own browser, they can extend it to recognize handles and retrieve documents from digital repositories that use the architecture CNRI is developing. Once the architecture and related protocols are more fully implemented, equivalent services will be provided in a form accessible through other browsers.

Frequently Asked Questions (FAQ) about Java.
[At http://sunsite.unc.edu/javafaq/javafaq.html.]

Home page for the Serials Industry Systems Advisory Committee (SISAC).
[At http://www.faxon.com/Standards/SISAC.html].

SISAC is an industry group concerned with standards for transmitting information about serial publications. The group was active in the development of the ANSI/NISO Z39.56 standard for the Serial Item and Contribution Identifier (SICI).

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(6/24/96)