Appendix C. Linking from Digital Objects to Collection Descriptions

The following guidelines apply to specialized use of the METS <mdRef> Metadata Reference element to create links from digital objects to associated, parent-level collection descriptions (represented either in the form of a MARC record or in the form of an EAD finding aid content file). Note that particular METS profiles may provide for more specific guidelines on use of the <mdRef> element for this or other purposes.

If the collection description is encoded in a MARC record, then encode the entire URL for the MARC record in a <mdRef> Metadata Reference HREF attribute of the object's METS wrapper. Include a MDTYPE attribute (see the bolded examples). Note that it may be difficult to generate a static and durable URL for particular MARC records, depending on local OPACs:

Example:
<METS:dmdSec ID='DMR1'>
<METS:mdRef LOCTYPE='URL' MDTYPE='MARC' xlink:href='http://antpac.lib.uci.edu/search/tkim+ha/tkim+ha/1%2C3%2C3%2CB/
frameset&amp;FF=tkim+ha+papers+1983+1999&amp;1%2C1%2C'/>
</METS:dmdSec>

If the collection-level description is encoded as an EAD finding aid, then use the following procedures:

1. Obtain the Archival Resource Key (ARK) URL for the finding aid that you would like to link the object to. (For finding aids already submitted to the CDL, the finding aid ARK URL can be obtained by viewing the finding aid online in CDL access systems).

   The ARK is a machine-readable unique identifier scheme for persistent access to digital resources managed by the CDL. Because ARKs are specially constructed and globally unique identifiers, their production and management is controlled by the CDL. For more information on the use of ARKs at the CDL and obtaining new ARKs, please see the CDL ARK service description.

   In some cases, you may be creating objects that will link to a finding aid that has not yet been created or completed (and will be submitted to the CDL at a later time). To obtain a new "placeholder" ARK for the finding aid, contact the CDL or mint an ARK locally using a CDL tool. At the point that you create the finding aid, encode the ARK within the <eadid> identifier attribute (see the bolded example). Only encode the portion of the ARK beginning with "ark:/...", and not the entire ARK URL:

   Example of EAD finding aid with ARK encoding:
   <eadid countrycode="us" identifier="ark:/13030/kt4w10133d" mainagencycode="CU-SC" publicid="PUBLIC "-//University of California, Santa Cruz::University Library::Special Collections//TEXT (US::CU-SC::MS 74::John Cage Mycology Collection)//EN" "ms74.sgm">ms74.xml</eadid>

2. Encode the entire ARK URL for the finding aid in a <mdRef> metadata reference HREF attribute of the object's METS wrapper. There are two possible methods for doing this. [Note: the second method will require additional and more intensive finding aid encoding].
   • Link the digital object to the beginning of the EAD finding aid. Include the ARK URL for the finding aid in the HREF attribute as well as MDTYPE and LABEL attributes (see the bolded examples).

     Example of object with link to the beginning of an EAD finding aid:
     <METS:dmdSec ID="DMR1">
     <METS:mdRef LOCTYPE="URL" MDTYPE="EAD" LABEL="Arnold Rubin Papers"
     xlink:href="http://www.oac.cdlib.org/findaid/ark:/13030/kt7489n8zj"/>
     </METS:dmdSec>

   • Link the digital object to the place in the EAD finding aid where the child-level digital object is described. Include the ARK URL for the finding aid in the HREF attribute, MDTYPE and LABEL attributes, and a unique identifier ID value (see the bolded examples).

     Example of object with link to specific section of an EAD finding aid:
     <METS:dmdSec ID="DMR1">
     <METS:mdRef LOCTYPE="URL" MDTYPE="EAD" LABEL="Arnold Rubin Papers"
     xlink:href="http://www.oac.cdlib.org/findaid/ark:/13030/kt7489n8zj" XTPR="xpointer(id('xyzj0098'))"/>
     </METS:dmdSec>

     The LABEL value should be the title for the collection that the object is related to (e.g., "Arnold Rubin Papers"). This should be the same title used for the collection in the associated finding aid.

     The unique identifier serves as an anchor point that links the object to a specific point in the finding aid, and vice versa. Therefore, it must be present in the object in addition to the specific point in the finding aid. The value of the unique identifier must be unique for the finding aid. The unique identifier must also comply with rules for IDs specified in the W3C's XML Schema Part 2: Datatypes. Namespaces must start with a letter and can include letters, digits, periods, hyphens, and underscores. Colons are not allowed.

     The same unique identifier ID value also needs to be encoded at the appropriate <archdesc> Archival Description or <c0x> Component level where the object(s) is described or implied in the finding aid. Encode the unique identifier (see bolded example) within an ID attribute for that <c0x> Component tag.

     Example of EAD encoding:
     <c02 id="xyzj0098" level="item">
     <did>
     <container type="box" label="Flat file">7</container>
     <unittitle>Ushiwaka and Benkei duelling on Gojo Bridge or Gojo Bridge, an episode from the Life of Yoshitsune, Chronicles of Yoshitsune, <unitdate>1881</unitdate>.
     </unittitle>
     <dao role="http://oac.cdlib.org/arcrole/link/image" href="http://ark.cdlib.org/ark:/13030/kt4p3005qx/"></dao>
     </did>
     </c02>

3. Create or update your finding aids to link to their associated objects, following the specifications outlined in the Online Archive of California Best Practice Guidelines for Encoded Archival Description (OAC BPG EAD), Sections 4.4.5 and 4.5.

   Do not add linking information to a finding aid prior to submitting the associated objects.

   The link from a finding aid to an object or group of objects can be made at any level (i.e., collection, series, subseries, file, or item level) in the finding aid, but it should be made at the level where the object(s) is described or implied in the finding aid.

   Creating links from finding aids to objects can be done two ways:

   • Link from a specific level in the finding aid (e.g., collection, series, etc.) to a group of objects, by linking to a search query for the group of objects in CDL access systems. This is most practical when linking from the collection level or major subdivision to the entire group of objects represented by that level of description. Note that you will be creating a link to a "canned" search for a group of objects, not to an individual or specific object. For an example, see the Redwood City Public Library's Morrish Collection.
   • Link from a specific level in the finding aid (e.g., file- or item-level) to a specific, individual object. This is most practical when linking from the file or item level to an individual object.