The state of the art and practice in digital preservation

Journal of Research of the National Institute of Standards and Technology, Jan, 2002 by Kyong-Ho Lee, Oliver Slattery, Richang Lu, Xiao Tang, Victor McCrary

The goal of digital preservation is to ensure long-term access to digitally stored information. In this paper, we present a survey of techniques used in digital preservation. We also introduce representative digital preservation projects and ease studies that provide insight into the advantages and disadvantages of different preservation strategies. Finally, the pros and cons of current strategies, critical issues for digital preservation, and future directions are discussed.

Key words: digital preservation; emulation; encapsulation; migration; standardization; XML.

1. Introduction

Information preservation is one of the most important issues in human history, culture, and economics, as well as the development of our civilization. While earliest information was recorded in carvings on stone, ceramic, bamboo, or wood, the development of civilization paved the way for new storage media and techniques for recording information, such as writing on silk or printing on paper. Eventually we were able to put photographic images on film and music on records. A revolutionary change occurred in the information storage field with the invention of electronic storage media.

With the advent of high-performance computing and high-speed networks, the use of digital technologies is increasing rapidly. Digital technologies enable information to be created, manipulated, disseminated, located, and stored with increasing ease. Ensuring long-term access to the digitally stored information poses a significant challenge, and is increasingly recognized as an important part of digital data management (1,2).

The evolution of data storage media and the development of the preservation technology can be described as shown in Fig. 1. This diagram lists the various media used in data storage (both digital and analog) and the techniques needed to ensure that the data on them is preserved. It also highlights the trend from analog to digital/optical storage media and indicates the transfer of data from one generation of media to the next. It is clear that while it is easier to create, amend, and distribute digital data, the media storing this data such as optical discs are not as robust as traditional analog media such as paper or film. In view of modern information preservation requirements, this paper will focus on the aspects of the technical strategies used in digital information preservation.

Digital preservation involves the retention of both the information object and its meaning. It is therefore necessary that preservation techniques be able to understand and re-create the original form or function of the object to ensure its authenticity and accessibility. Preservation of digital information is complex because of the dependency digital information has on its technical environment. Furthermore, as newer digital technologies rapidly appear and older ones are discontinued, information that relies on obsolete technologies soon becomes inaccessible. Therefore, digital resources present more difficult problems than conventional analog media such as paper-based books (3).

Recently, several approaches for digital preservation have been identified and presented. Conventional methods are mainly technology emulation, information migration, and encapsulation (4,5,6,7,8). However, there is a lack of proven preservation methods to ensure that the information will continue to be readable.

To promote a solid understanding of the pros and cons of different preservation techniques, this paper tries to present a comprehensive survey of them through a review of a wide range of literature and representative projects. We suggest a preservation strategy based on XML (eXtensible Markup Language) [9] for interoperability and interchangeability of preserved digital information. The most appropriate preservation strategy should be determined by considering various aspects including cost-effectiveness, legal restrictions, and user access requirements. However, as stated earlier, this paper particularly focuses on the technical issues of preservation.

This paper is organized as follows. Section 2 summarizes various techniques for digital preservation. Their advantages and disadvantages are presented through a literature survey. By introducing current projects and case studies, the application of these preservation techniques is described in detail in Sec. 3. Finally, points of discussion and a summary are given in Sec. 4.

2. Digital Preservation Techniques

This section introduces the current strategies for digital preservation. Techniques for the preservation of digital information include technology preservation, technology emulation, information migration, and encapsulation.

Digital resources can be stored on any medium that can represent their binary digits or bits, such as a CD-ROM or a DVD. Rothenberg [10] defines a bit stream as an intended meaningful sequence of bits with no intervening spaces, punctuation, or formatting. To preserve that bit stream, the first requirement is to ensure that the bit stream is stored on a stable medium. If the digital medium deteriorates or becomes obsolete before the digital information has been copied onto another medium, the data will be lost.