Introduction

It is a truism that preserving digital objects is quite different from preserving physical ones. While a 400-year-old book may be held and read today, digital content can be made manifest only through the use of specific hardware and software. This dependency on a technological intermediary means that not only must the object itself be kept secure and intact, as is true for all preservation, but that the means to reveal its content must also be maintained. In order to do this, a preservation agency must know a great deal about the object and the environment in which it can be used. Collectively, the information that an archive will need to ensure the survival of digital objects over long periods is called preservation metadata.

In recent years, the digital library community has dedicated focused effort to three main areas related to preservation metadata:

Digital repositories routinely contain many kinds of information about the objects they manage. Some of this information supports the administration of the archive, such as information about the depositor, the rights holders and the contractual agreement outlining the respective rights and obligations of the depositor and the repository. Additional information may support functions such as discovery, storage management and access management. All such information may also be useful or even necessary for preservation. However, there are additional categories of information that primarily or exclusively exist to enable long-term preservation.

Techniques for preserving digital material are still in their infancy, with many fundamental questions of methodology and best practice still under debate. Most discussions about digital preservation have been theoretical: as of 2005, few digital archives have active preservation programmes. As experience in preserving digital information grows, understanding of the information that will be required in the preservation process will continue to evolve.