On Tue, 5 Aug 1997, Jean Marie Taylor wrote:

> I am cataloging a large group of digitized photographs. The
> images will be linked to the bibliographic records through
> field 856. In the past, we have only used \u in field 856. It
> has been suggested that we begin to use subfields \a and \2 so
> that the hostname can be globally changed more easily if the
> images are moved to another server.
>
> This is the example I was given:  856 7_  \u /GP/00001 \2 http
> \a aries.vsla.edu.  (/GP/00001 is the sub-directory and file
> name for 1 image.)
>
> I can't find an example of \u that only includes the
> sub-directory and file name. All the examples I have found
> shown the complete URL which will not address the problem of
> making future changes easier.

Subfield $a is used for the host name when the elements of the URL are
parsed into separate subfields.  The host name is the first part of the
URL following by the access method, a colon and 2 slashes.  Subfield $u is
defined as a URL, and it wouldn't be appropriate to include a subdirectory
and filename.

The Library of Congress wrestled with the same issues about changability
of the URL.  For a time, we have used the following subfields to include
the information in field 856; a document locator system at LC stores the
information concerning the exact location of the resources.
        $d      Directory name
        $f      File name
We then used $2 file, which is an access method defined by the URL
standard to mean that it's a local implementation. For further information
see Guidelines on the Use of Field 856
(http://www.loc.gov/marc/856guide.html).

I suppose you could use the $a for the host name, but rather than use the
$u, use the $d and $f.

We expect to go to Uniform Resource Names (a unique, persistent name
rather than location) at some point in the future.

 > > Also, I am wondering about the
> order of the subfields. Does that matter?

Order of subfields is not specified, except that $3 usually comes first if
present.

>  Thanks in advance for any help!
> --
> Jean Marie Taylor
> Consultant, Electronic Products
>   & Automation Services
> The Library of Virginia
> 800 East Broad Street               (voice)  (804) 692-3764
> Richmond, Virginia  23219-1905      (fax)    (804) 692-3771
> http://leo.vsla.edu                 (e-mail) [log in to unmask]
>

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^^  Rebecca S. Guenther                                   ^^
^^  Senior MARC Standards Specialist                      ^^
^^  Network Development and MARC Standards Office         ^^
^^  Library of Congress                                   ^^
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