Newsletter Discussion

Abstract

As an XML schema, the "Metadata Object Description Schema" (MODS) is intended to be able to carry selected data from existing MARC 21 records, as well as to enable the creation of original resource description records. METS schema provides a useful standard for the exchange of digital library objects between repositories, as well as to associate a digital object with behaviours or services.

METS and MODS

-a talk by Krishnamoorthi.BM.

Introduction

Maintaining a library of digital objects of necessity requires maintaining metadata about those objects. The metadata necessary for successful management and use of digital objects is both more extensive than and different from the metadata used for managing collections of printed works and other physical materials. While a library may record descriptive metadata regarding a book in its collection, the book will not dissolve into a series of unconnected pages if the library fails to record structural metadata regarding the book's organization, nor will scholars be unable to evaluate the book's worth if the library fails to note that the book was produced using a Ryobi offset press. The same cannot be said for a digital version of the same book. Without structural metadata, the page image or text files comprising the digital work are of little use, and without technical metadata regarding the digitization process, scholars may be unsure of how accurate a reflection of the original the digital version provides. For internal management purposes, a library must have access to appropriate technical metadata in order to periodically refresh and migrate the data, ensuring the durability of valuable resources.

A METS document consists of seven major sections:

1. METS Header - The METS Header contains metadata describing the METS document itself, including such information as creator, editor, etc.

2. Descriptive Metadata - The descriptive metadata section may point to descriptive metadata external to the METS document (EAD finding aid maintained on a WWW server), or contain internally embedded descriptive metadata, or both. Multiple instances of both external and internal descriptive metadata may be included in the descriptive metadata section.

3. Administrative Metadata - The administrative metadata section provides information regarding how the files were created and stored, intellectual property rights, metadata regarding the original source object from which the digital library object derives, and information regarding the provenance of the files comprising the digital library object (i.e., master/derivative file relationships, and migration/transformation information). As with descriptive metadata, administrative metadata may be either external to the METS document, or encoded internally.

4. File Section - The file section lists all files containing content which comprise the electronic versions of the digital object. <file> elements may be grouped within <fileGrp> elements, to provide for subdividing the files by object version.

5. Structural Map - The structural map is the heart of a METS document. It outlines a hierarchical structure for the digital library object, and links the elements of that structure to content files and metadata that pertain to each element.

6. Structural Links - The Structural Links section of METS allows METS creators to record the existence of hyperlinks between nodes in the hierarchy outlined in the Structural Map. This is of particular value in using METS to archive Websites.

7. Behavior - A behavior section can be used to associate executable behaviors with content in the METS object. Each behavior within a behavior section has an interface definition element that represents an abstract definition of the set of behaviors represented by a particular behavior section. Each behavior also has a mechanism element which identifies a module of executable code that implements and runs the behaviors defined abstractly by the interface definition.

MODS

The Library of Congress' Network Development and MARC Standards Office, with interested experts, has developed a schema for a bibliographic element set that may be used for a variety of purposes, and particularly for library applications. As an XML schema, the "Metadata Object Description Schema" (MODS) is intended to be able to carry selected data from existing MARC 21 records as well as to enable the creation of original resource description records.

Top Level Elements:

Root Elements:

mods
modsCollection

Uses

• to represent metadata for harvesting

• for original resource description in XML syntax

• for representing a simplified MARC record in XML

• for metadata in XML that may be packaged with an electronic resource

Advantages

• The element set is richer than Dublin Core

• The element set is more compatible with library data than ONIX

• The schema is more end user oriented than the full MARCXML schema

• The element set is simpler than the full MARC format

Conclusion

The METS schema provides a flexible mechanism for encoding descriptive, administrative, and structural metadata for a digital library object, and for expressing the complex links between these various forms of metadata. It can therefore provide a useful standard for the exchange of digital library objects between repositories. In addition, METS provides the ability to associate a digital object with behaviours or services. The above discussion highlights the major features of the schema, but a thorough examination of the schema and its included documentation is necessary to understand the full range of its capabilities.

References

http://www.loc.gov/standards/mets/METSOverview.v2.html
http://www.loc.gov/standards/mods//