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EAD 2002 Schema

The EAD Schema Working Group (SAA/EADWG) is pleased to announce the release of the EAD 2002 Schema.

The EAD 2002 Schema is available in two syntaxes: Relax NG Schema (RNG) and W3C Schema (XSD).

Note: Comments, questions, and error reports should be sent to the EAD listserv with the subject line: Schema Comment

Listserv address: EAD@LOC.GOV

The RNG version is the maintenance and therefore authoritative version. The XSD version is derived from the RNG using Trang, with minor manual editing subsequent editing.

EAD DTD / SCHEMA RELATIONSHIP

With one exception (XLink elements and attributes), the EAD Schema is a subset of the EAD 2002 DTD.

The Xlink compatible elements and attributes in the DTD have been made compliant by implementing XML Namespace. As a result, DTD compliant instances containing ANY of the XLink tags and attributes will not validate against the Schema. These instances must be converted into XLink compliant tags and attributes. The EAD Schema WG has provided an Alpha XSLT for this conversion. A parameter on line 51 allows the user to specify whether the resulting schema should have RNG or W3C addressing information:

dtd2schema.xsl

Instructions for Using dtd2schema.xsl (PDF file, 2 p.)

The following elements and their XLink-specific attributes are impacted by this change:

   arc archref
   bibref
   dao daogrp daoloc
   extptr extptrloc extref extrefloc
   linkgrp
   ptr ptrloc
   ref refloc resource
   title

For example, the following DTD compliant tag:

Must be converted to the following:

Do note also that while RNG does support external entities, XSD does not. Thus @entityref must be resolved and converted to @xlink:href on XLink "locator" tags. Do note also that @xlink:href is a required attribute on XLink "locator" tags, and thus using RNG will require the presence of this attribute on the relevant tags.

With the exception of the XLink tags and attributes, a Schema valid instance will be a DTD valid instance. However, because of the imposition of datatype contraints on specific attribute values, a DTD valid instance may not be Schema valid.

The following attributes are impacted by the imposition of datatype constraints:

   @normal on <unitdate> and <date>: constrained to date and date range subset of ISO 8601
   @repositorycode: constrained to ISO 15511 (ISIL)
   @mainagencycode: constrained to ISO 15511 (ISIL)
   @langcode: constrained to ISO 639-2 alpha-3 code list
   @scriptcode: constrained to ISO 15924 code list
   @countrycode: constrained to ISO 3166-1 alpha-2 code list

Document: Switching from EAD DTD to XSD

SCHEMA NOTES

In preliminary testing, many of the attribute values intended by encoders to be compliant with each relevant ISO standard were found to be incorrect. Thus scriptcode="latn" for the Latin script is incorrect. The correct code for the Latin script is "Latn". The case of the character matters!!

Attribute validations errors indicate that the attribute value does not conform to the ruling ISO standard.

Publisher: Society of American Archivists and the Library of Congress

Funding: National Historical Publications and Records Commission

Editors (SAA/EADWG/EAD Schema Working Group):

Francoise Bourdon (Bibliothèque nationale de France)
Terry Catapano (Columbia University)
Jerry McDonough (University of Illinois)
Lee Mandell (New York University)
Chris Prom (University of Illinois)
Stephen Yearl (Yale University)
Daniel Pitti (University of Virginia), Chair

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