Introduction
There is as yet no viable long-term strategy to ensure that digital information will be readable into the future (Rothenberg, 1999b, p.v)
Maintaining access to digital resources over the long-term involves interde- pendent strategies for preservation in the short to medium term based on safeguarding storage media, content and documentation, and computer soft- ware and hardware; and strategies for long-term preservation to address the issues of software and hardware obsolescence (Jones and Beagrie, 2001, p.95) High-level models for persistent repositories indicate that digital archiving and long-term preservation is best handled by separating archival storage of bits (storage management) from data management, logical representations, and higher level services that can be built on top of a persistent storage architec- ture (Workshop on Research Challenges in Digital Archiving and Long-term Preservation, 2003, p.xiv)
This chapter provides an overview of the range of principles, strategies and practices that we have available to us at present for digital preservation. It also examines the requirements for approaches that will remain viable and effective in the future. It attempts to put the approaches identified to date, both those in current use and those that are emerging, into a useful context so that they can be reflected on. Such reflection may point to clearer ways forward in the future.
A distinction is made between principles, strategies and practices. Principles are general ways of thinking, usually at the conceptual level; for example, it is a principle to use standards where they exist. Strategies are more concrete plans to achieve a particular long-term aim, as plans designed to achieve a particular long-term aim; an example of a strategymight be to limit the number 1111
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of standard file formats that are to be maintained. Practices are even more specific. A practiceis what you need to do to implement and maintain a strategy, for example, the application of the necessary technology to maintain the stan- dard file formats selected. Practices encompass technologies – the ‘machinery and equipment based on the application of scientific knowledge for practical purposes’ (as defined in the Concise Oxford English Dictionary). The terminology is used in different ways through the literature. For instance, ERPANET (the Electronic Resource Preservation and Access Network) uses the word technology inclusively to cover all hardware and software as well as methods and proce- dures: ‘technology are all means that serve the purpose of preserving digital objects for as long as it [sic] is needed (ERPANET, 2003, p.2).
Others have developed typologies of the principles, strategies and practices.
(Typologyis used here in the sense of systematic grouping to help understanding of things being studied by identifying attributes or qualities among them that link them together.) These typologies range from limited lists with a small number of categories, such as that of Lim, Ramaiah and Pitt (2003), to more sophisticated versions, such as Rothenberg’s typology (2003). These are exam- ined in more detail later in this chapter.
Why might dwelling on these typologies help us to address digital preserva- tion concerns? The UNESCO Guidelines suggest that strategies ‘are still evolving’
and that ‘there is, as yet, no universally applicable and practical solution to the problem of technological obsolescence for digital materials’ (UNESCO, 2003, pp.122,124–125). Alan Howell notes 16 strategies to ensure the long-term sus- tainability and accessibility of digital objects (Howell, 2004, pp.31–32). There are many ways of characterizing the range of strategies. For example, we can distinguish between passive approaches (such as improving digital storage media, improving storage and handling practices) or activeapproaches (such as refreshing, migration, emulation, encapsulation, normalization, and replication).
Research and implementation work proceeds into all of these and more, for example, replication (the LOCKSS (Lots of Copies Keep Stuff Safe) Project), digital mass storage systems, and trusted repositories. The contention of this chapter is that, because such a wide range of approaches, strategies and prac- tices is in use or development, determining their desirable characteristics could guide us to more rapid development of viable mechanisms to address the signif- icant threat of loss of digital information. Developing such typologies could indeed heighten our understanding.
The UNESCO Guidelines identify some strategies that are likely to be viable in the long term: ‘the use of standards for data encoding, structuring and descrip- tion’, emulation, and migration of data (UNESCO, 2003, pp.124–125). The Guidelines also note some principles that lie behind current approaches to preserving digital materials (UNESCO, 2003, section 17.11–12). Despite guid- ance such as this, the list of possible strategies remains long and bewildering (see Figure 6.1). From this a smaller number of strategies is likely to emerge.
This chapter first notes some of the history of the development of principles and strategies for digital preservation. It then notes strategies that are being applied. Finally, some existing typologies of approaches, strategies and practices are described, and a further typology is proposed.
100 Overview of Digital Preservation Strategies
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Principle, Strategy, Practice Also referred to in the literature as . . .
Analogue backups Output to permanent paper or microfilm, page image techniques; Save page-images of artifacts Backup and restore
Bit-stream copying
Canonicalization Translate artifacts into standard or ‘canonical’
forms Digital archaeology Data recovery
Durable/persistent media Improved storage media
Emulation Technology emulation
Encapsulation Creating a persistent object; Digital tablets Improving handling and storage
Mass storage Digital mass storage systems Media transfer
Metadata
Migration Format migration; Normalization then migration;
Software migration; Backwards compatibility and version migration
Persistent archives
Persistent object preservation
Policy development Developing policy, specifications and procedures Refreshing Refreshing data; Medium refreshing
Replication Replication; Redundancy; Keeping multiple copies Standard data formats Normalization; XML; Restricting the range of
formats to be managed; Long term formats Standards Reliance on standards; Use of standards Technology preservation Preserve technology; Maintain old technology;
Technology watch
Viewers Viewers for obsolete formats
Virtual machines Virtual machines; UVC (Universal Virtual Computer) approach
Other (not readily categorized) Save source-code of rendering software (for future reverse-engineering); Extract and save core contents of artifacts; Software repositories;
Web domain harvesting; Formalization (replace artifacts by formal descriptions of themselves);
Data extraction and structuring Figure 6.1 Digital Preservation Principles, Strategies and Practices
(From Kransch, 1998; Soete, 1997, p.7; Hendley, 1998, p.4; Bullock, 1999; Woodyard, 2000;
Heazlewood, 2000, pp.180–184; Howell, 2000, pp.133–134; Van der Werf, 2002; Howell, 2001, pp.142–146; Strang, 2003; Walton, 2003, p.5; Lim, Ramaiah and Pitt, 2003, p.121; Digital Preservation Testbed, 2003, p.29; Rothenberg, 2003; UNESCO, 2003, pp.126–149; Smith, 2003, p.43; Beagrie, 2003, pp.15–16; Kenney et al., 2003)
Introduction 101