Preservation of Digital Information
Strategies for Preserving Digital Objects
In 1994, the Commission on Preservation and Access and The Research Libraries Group (RLG) formed the Task Force on Digital Archiving. The 1996 Task Force report outlined the challenges for digital preservation and made some recommendations.
The following strategies were proposed as components of a digital preservation program:
Refreshing data
- addresses the decay, change, or obsolescence of physical formats - media on which we store files
- involves periodically moving a file from one physical storage medium to another. Changes to physical storage devices require this to be an ongoing process.
The Digital Task Force also proposed two solutions to deal with file format changes (eg. files created by outdated versions of software)
Emulation and Migration
Migration
- involves moving files from one file encoding format to another. For example, upgrading a file type to the newest version of your particular software product
Emulation
- focusses on the application rather than the files produced. Emulation tries to recreate application environments on which the original files can run.
Ideally, a combination of Refreshing with either Emulation or Migration should be adopted as a preservation strategy for digital information objects.
For a detailed examination of the issues and differences between Emulation and Migration, see
Emulation
vs. Migration: Do Users Care
Margaret Hedstrom and Clifford Lampe
RLG DigiNews
December 15, 2001, Volume 5, Number 6
PADI -- Preserving Access to Digital Material
Migration
Emulation
The 'Storage and Preservation' chapter in the following document provides a useful overview of the issues to consider for preserving digital images:
Creating Digital Resources for the Visual Arts: Standards and Good Practice
Visual Arts and Data Service
AHDS Guides to Good Practice
Archival Images
Any project creating digital images, even if the main purpose of the project is to create images for the Web, should create master images. These will be images captured at a high resolution, on which no manipulation or change is made. Copies of these archival files can be made and used for later projects, but the original captured files should always be maintained and preserved.
Preservation Metadata
Recording preservation metadata should be a key component of a digital preservation strategy. This type of information will often be administrative or structural in manner, and will include information about the date of capture, the capture device, change history, and other information about the files, including relationships to other files. This metadata is different from descriptive information about the content of the file, which may be used for resource discovery. Some projects have developed extensive sets of preservation metadata.
OCLC (Online Computer Library Center, Inc) and RLG are collaborating on digital archiving initiatives. One of the goals of the initiative is to develop a comprehensive preservation metadata framework.
Information about this initiative can be found at:
http://www.oclc.org/research/projects/pmwg/default.htm
One of the reports from this initiative is already available. It is a fifty page paper on preservation metadata, and its appendices include some samples of preservation metadata elements required by sample projects:
Preservation Metadata for Digital Objects: A Review of the State of the Art
A White Paper by the OCLC/RLG Working Group on Preservation Metadata
For information about some of the preservation initiatives outlined in the paper:
CEDARS -- Curl Exemplars in Digital Archives
This United Kingdom project objectives include
- promoting awareness of digital preservation issues
- identification of strategic frameworks for developing digital collection management policies
- developing guidelines for long-term preservation
Nedlib-- Networked European Deposit Library
This collaborative effort among European national libraries aims to develop the infrastructure for a networked European deposit library, with a focus on preservation of electronic publications
National Library of Australia
Preservation Metadata for Digital Collections
The OCLC and RLG collaboration is also focussing on the OAIS (Open Archival Information System), which is an information model for handling archiving of physical and digital information.