Structural Metadata Dictionary for LC Digital Objects

External Pointers to Digital Objects


External pointers to digital objects include MARC record 856 fields, HTML hypertext links (HREFs), and Encoded Archival Descriptions (EADs).

Such pointers can contain one of the following:

*   In MARC record 856 fields the "g" subfield is used to hold URNs and the "u" subfield is used to hold URLs. For current LC plans for using 856 subfields g and u, click here.


Uniform Resource Name (URN)



HTTP Uniform Resource Locator (URL)



HTTP Uniform Resource Locator (URL) where the Local Object ID contains a URN and the host/domain name is that of the server to be used in resolving the URN to a URL.



LC Plans for Using MARC 856 subfields g and u:

Ultimately, the Library of Congress will record the Uniform Resource Name (URN) in the 856 field of the MARC bibliographic record associated with an LC collection item that has been digitized. Such URNs will be constructed as "handles" and will be placed in subfield g (856 $g). Example:  $gurn:hdl:loc.ndlp/amrlp.3a16116

In the near term, however, both URLs and URNs will be recorded in the 856 field:

This is being done because services for resolving URNs into locations (URLs) are not yet widely available. Once URN resolvers are widely available, LC will stop recording the URL of the proxy server as described above and just record the URN in 856$g. Exactly when this will happen is unclear at this time (01/12/98).


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Created: 9/12/97      Revised: 02/09/98
National Digital Library Program - Digital Repository Development Project
Comments: vvit@loc.gov