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2.2 Linking Elements

2.2 SECTIONS: Internal LinkingExternal Linking

Description:

There are seventeen elements in EAD that can be used to establish links: fifteen manage links directly, while two (<daogrp> and <linkgrp>) are wrapper elements that consolidate multiple, related links. Linking elements are discussed here under the general categories of internal links (within the EAD document) and external links (to other documents).

See Also:

Section 2.2.1, Internal Linking Go to Section

Section 2.2.2, External Linking Go to Section

Subelements:

• <arc> See 2.2.1 Internal Linking and 2.2.2, External Linking
• <archref> See 2.2.2, External Linking
• <bibref> See 2.2.2, External Linking
• <dao> See 2.2.2, External Linking
• <daogrp> See 2.2.2, External Linking
• <daoloc> See 2.2.2, External Linking
• <extptr> See 2.2.2, External Linking
• <extptrloc> See 2.2.2, External Linking
• <extref> See 2.2.2, External Linking
• <extrefloc> See 2.2.2, External Linking
• <linkgrp> See 2.2.1, Internal Linking
• <ptr> See 2.2.1, Internal Linking
• <ptrloc> See 2.2.1, Internal Linking
• <ref> See 2.2.1, Internal Linking
• <refloc> See 2.2.1, Internal Linking
• <resource> See 2.2.1 Internal Linking and 2.2.2, External Linking
• <title> See 2.2.2, External Linking

Comments:

Extensive information about linking can be found in Chapter 7 of the EAD Application Guidelines. Check the Tag Library for current values of attributes.

Revision Date: 05/01/08

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2.2.1 Internal Linking

Description:

Internal linking enhances the ability to navigate a finding aid via explicit links between related information appearing in different places in the finding aid. Extensive information about linking can be found in Chapter 7 of the EAD Application Guidelines.

LC Practice requires the use of the TARGET, ACTUATE, and SHOW attributes with internal linking elements, and recommends the use of <ref> over <ptr> for internal linking.

See Also:

Section 3.3.8.3, Indexes Go to Section

Section 2.2.2, External Linking Go to Section

Other Attributes:

• target (value of id assigned to target of link) Required
• actuate="onrequest" (means user needs to click on link for target to be displayed) Required
• show="replace" (target is displayed in place of the text just viewed) Required

See Tag Library for full list of attributes and their values.

Subelements:

Simple Linking within the Finding Aid:

• <ref> (links with text)
• <ptr> (empty links--no text) may be bundled using <ptrgrp>

Additionally, <indexentry> may be used within the index to bundle <ref>, <ptr>, or <ptrgrp>.

Extended Linking within the Finding Aid (must be bundled using <linkgrp>)

• <arc> (rules for traversal among resources in extended link)
• <refloc> (locator links with text)
• <ptrloc> (empty locator links--no text)
• <resource> (local resource participating in extended link)

Tagging Example 1:

Cross-reference from Hart linked to target (Rodgers)

Display of Tagging Example 1:

Cross-reference from Hart linked to target (Rodgers)

Box 135   Hart, Lorenz See Container 176, Rodgers, Richard
...
Box 176   Rodgers, Richard, and Lorenz Hart, I Married an Angel,
          [1938]

Comments:

• All links must have targets. Set the TARGET attribute for a reference with a brief unique alpha or alphanumeric identifier for the object of the link; id's must begin with an alphabetic character. For example, a container list cross reference, "See Container 17, Smith, Anna" might have attribute target="smith17". To make the link work, set the attribute id="smith17" for the <unittitle> in Container 17 to which the link should go. See Example 1.
• See Section 3.3.8.3 for a discussion of <ptrgrp>, <ptr>, and <ref> in relation to indexes.
• See the Application Guidelines, 7.2.3 for an explanation of the extended linking and elements <refloc> and <ptrloc>. Remember to check the EAD 2002 Tag Library for new elements <arc> and <resource>, and for current values of attributes for linking elements.

Revision Date: 1/26/08

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2.2.2 External Linking

Description:

External linking refers to links from a finding aid to another electronic resource, which may be another encoded finding aid, a digital archival object (<dao>), an external image or file not from the archival collection (e.g., the LC logo or an illustration), or a web page. Extensive information about linking can be found in Chapter 7 of the EAD Application Guidelines.

LC Practice requires the use of the HREF, ACTUATE, and SHOW attributes with external linking elements.

See Also:

Section 2.1.2, Paragraph (use of linking elements within) Go to Section

Section 2.2.1, Internal Linking Go to Section

Section 3.1.2, File Description Go to Section

Section 3.3.1.11, Digital Archival Object Group Go to Section

Section 3.3.3.8, Alternate Form of the Materials Available (examples of <extref> to URLs, discussion of <daogrp>) Go to Section

Section 3.3.7.4, Expanded Description of Components (<daogrp> at component level) Go to Section

Section 3.3.8.1, Bibliographies (<bibref> and <archref> as linking elements) Go to Section

Section 3.3.8.5, Related Material (<bibref> and <archref> as linking elements) Go to Section

Section 3.3.8.6, Separated Material (<bibref> and <archref> as linking elements) Go to Section

Other Attributes:

Simple Linking:

• href (target of link) Required
• actuate="onrequest" (means user needs to click on link for target to be displayed) or "onload" (means target displayed automatically, e.g., LC logo) Required
• show="new" (target resource displayed in a new browser window) or "embed" (target resource displayed at point of link) Required

See Tag Library for full list of attributes and their values.

Extended Linking (<daoloc>):

• href (target of link) Required
• role (MIME type of target)

See Tag Library for full list of valid attributes and their values for this and for other extended linking elements.

Subelements:

Simple Linking:

• use <extptr> for the LC logo (in <eadheader>) or any illustrative matter which should be displayed inline and is not from the collection described
• use <extref> for external links such as to a Library web page
• use <archref> to link to other archival collections. For instance, this may be another finding aid (preferably EAD), or to a web page, database, or catalog record for the archival collection.
• use <bibref> to link from a bibliographic citation to an online version of the work
• use <title> to link to a title to an online version of the work

Extended Linking:

• use <arc> to specify rules for traversal among resources in an extended link
• use <daoloc> for an object within <daogrp>. <daogrp> is used as a wrapper for one or more archival objects.
• rather than using <dao> for a single archival object, use <daoloc> within <daogrp> instead
• use <extrefloc> for external reference extended references
• use <extptrloc> for external pointer extended references
• use <resource> to specify local resources participating in an extended link

Tagging Example 1a:

XML prolog with entity declarations and linking elements for LC logo

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE ead PUBLIC "+//ISBN 1-931666-00-8//DTD ead.dtd
(Encoded Archival Description (EAD) Version 2002)//EN"
"http://lcweb2.loc.gov/xmlcommon/dtds/ead2002/ead.dtd" 
[
<!ENTITY lcseal SYSTEM "http://lcweb2.loc.gov/xmlcommon/lcseal.jpg"
NDATA jpeg>
]>

<ead>[Beginning of EAD finding aid]</ead>

Tagging Example 1b:

<daoloc> has an href value linking to American Memory presentation of Hannah Arendt Papers series

Display of Tagging Example 1b:

<daoloc> link goes to American Memory presentation of series contents

Correspondence, 1938-1976
  Items available online.

Comments:

XML Prolog:

• All finding aids should have information included in the XML prolog (the portion of the document which precedes the opening <ead> tag) in order to permit external linking. This information is included in the templates, and the full text of the prolog is provided in Example 1a.
• The entity declaration, "<!ENTITY lcseal SYSTEM ...> enables linking to the LC logo, which is stored in the ITS file system and is displayed with the PDF version of every LC finding aid.

Handles and Linking:

• Use the HREF attribute to set the target of the link from each linking element.
• If the target of a link is another EAD finding aid, a handle will be registered for the finding aid as part of standard procedures. The LC staff EAD web page contains examples of batch handle files for finding aids.
• If the target of a link is a stable web page, the HREF attribute will include its URL, and there is no need to register a handle.
• If the target of a link is not a stable URL, for instance the response to a cgi-bin query, consider registering a handle.

Revision Date: 10/20/10

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