g-term preservation of digital material requires a commitment to an ongoing set of processes to move digitized materials through each generation of technology. A strict adherence to all appropriate standards will increase the likelihood that digital objects will migrate into the next generation with the least loss of content, greatest efficiency, and the lowest cost.
We know that there is no permanent and durable medium for storing digital information. This leads to the need to test and refresh information at appropriate intervals. Copying data onto fresh media can re-start the life-expectancy clock. If, for example, we assume that a CD-Recordable disc will last for 20 years, burning a new copy every 10 years would be a process that could be followed to preserve the data, given an assumption that this media continues to be viable.
New media options continually emerge, with each successive generation offering more capacity at a lesser cost. Given this trend, it's likely that in most cases information will not be refreshed onto the same type of media, but will be moved onto the next generation. It wouldn't make sense, for example to refresh data held on 3 ½ inch diskettes onto the same kind of media. Rather, it would be more practical to copy the data onto CD-ROM or DVD.
Many digitized collections reside on online storage systems of some sort. These devices offer instant access to information, are highly reliable, and can be built for very large capacities. Yet we do not expect any given online system to last forever. Storage systems typically last 3-5 years and are replaced by faster and better ones. Online storage systems become obsolete very quickly. Cycles of migration of data in the online storage arena can be very short. These systems are also volatile. It's important to follow strict data management and disaster planning procedures to ensure that systems failures do not result in loss of information.
One of the most important strategies related to digital preservation involves taking advantage of open standards whenever available and appropriate, avoiding proprietary data formats when possible. Even though standards change and evolve, they are much more stable and reliable than proprietary formats that may be tied to the commercial success of a single vendor. Given choices, for example, between digitizing video into MPEG, an international standard, and a proprietary format such as RealMedia or Windows Media, it makes sense to use the standards-based format. It often means creating a master copy in the standard format, and deriving from it proprietary versions that can be used by a wider audience. In one project that I'm involved with, or strategy involves digitizing video into MPEG-2 format for preservation, and generating RealMedia files to be used for end-user access.
While these and other methods can be used as informal guidelines, the issue of digital preservation really demands a more structured and formal approach. To this end, a number of efforts have taken place in recent years that provide a structured framework for the design of an archive that meets the requirements of long-term preservation in addition to other areas of functionality. The culmination of these efforts is the Open Archival Information System, or OAIS.
OAIS: A comprehensive framework for digital preservation
The complexities involved with changing technologies and the need to create permanent digital collections has sparked a number of initiatives of some of the major players. Some of the important activities in this arena include the CEDARS project in the UK (http://www.leeds.ac.uk/cedars/); NEDLIB, a collaborative project of several European national libraries (http://www.kb.nl/coop/nedlib/); and the National Library of Australia's PADI initiative (http://www.nla.gov.au/padi/). OCLC and the Research Libraries Group (RLG) have been collaborating on this issue and have issued a report titled: “Attributes of a Trusted Digital Repository: Meeting the Needs of Research Resources” (www.rlg.org/longterm/attributes01.pdf).
The most definitive mod