Workbook on Digital Private Papers > Digital preservation strategies > Selecting the right preservation strategy
Selecting the right preservation strategy
Other preservation approaches
Encapsulation
Encapsulation is an essential element of many emulation approaches and also plays a key part in some other preservation strategies. It involves retaining a digital object in its original form as a bitstream, and encapsulating it along with instructions and whatever else might be necessary to maintain access to it in the future; this might include software viewers or software specifications for emulation, as well as comprehensive preservation metadata.
An Information Package as defined by the OAIS Model represents a form of encapsulation, in which the digital object is packaged together with: the Representation Information needed to interpret the bits appropriately for access; and Preservation Description Information, which includes information on provenance, context, reference and fixity.
The Virtual Machine approach is an extension to encapsulation in that an executable program is also packaged together with the digital object.
Technology preservation
Like emulation, this approach focuses on the technological environment rather than on the digital object. Instead of mimicking the original environment, it involves preserving the digital object together with all the actual hardware and software required to maintain access to the object; this includes operating systems, original application software and media drives. It could be argued that maintaining the original technology is the most effective and obvious means of preserving the look and feel of a digital environment, and there is certainly merit in keeping samples of old computer systems as a resource for researchers in the future; however, while it might offer a short-term solution, this is not a viable strategy for long-term digital preservation, for various reasons:
- Cost and space implications for acquiring and maintaining large quantities of hardware (from computers and peripherals to connectors) are prohibitive for many organisations.
- Older operating system and application software and appropriate licences must also be acquired and maintained.
- Over time the machines will degrade and ultimately fail, so the number of machines capable of reading certain types of old files will continually decrease.
- Technical support for both software and hardware will also disappear over time.
- Documentation for older computing environments can be difficult to locate.
Digital archaeology
Digital archaeology involves retrieving data from obsolete software or hardware environments, and obsolete or damaged media, such as punch cards, 8" floppy disks and the wealth of other removable media which have been used since the earliest days of computing. There are a growing number of specialist third party services offering to carry out digital archaeology, and it has been shown to be technically possible to recover bitstreams from damaged and obsolete media. Only trained specialists will be able to extract data in this way, using special hardware and software; for instance, in order to extract data from relatively recent, damaged, media, the British Library makes use of 'forensic' hardware, designed for use by law enforcement, intelligence, corporate and military agents who need to recover digital evidence from hardware in a way which ensures its authenticity.
Digital archaeology will form an inevitable part of the digital archivist's work for a long time to come; however pro-active our approach in working with donors and depositors, archives are still likely to contain obsolete or damaged data which we need to rescue from oblivion. Ultimately, however, digital archaeology is an emergency recovery strategy, not a pro-active and preventative approach to long-term preservation, because:
- It is much more costly than the other major preservation strategies and is unlikely to be cost-effective for any other than the most highly valued digital resources.
- Relying on digital archaeology means that the digital material which isn't necessarily highly valued (yet might still be useful to some researchers or have important evidential value) might not be rescued.
- If there is no accompanying metadata or documentation, it may be impossible to assess the value or usefulness of obsolete digital resources until after rescue has taken place, which may turn out to be a waste of resources.
- Digital archaeology techniques are unlikely to be successful in all cases.
- It requires a certain amount of technology preservation (see above).
If digital archaeology is successfully carried out as an emergency rescue measure, digital archivists must then process extracted files using the repository's policy and procedures and decide whether or not to retain the original media on which the creator stored their files. Some arguments in favour of retaining media include:
- The value of removable media as artefacts, especially if the record creator has annotated media labels.
- They constitute the 'original' version of the digital object.
- The future researcher may wish to experience the original environment.
- Future developments in technology may mean that more data can be extracted from the media.
Arguments against retaining media:
- Disks and other removable media are equivalent to the original files or packaging in which traditional archives arrive at the repository. Unless there is special significance in these (e.g. they have particular evidential value or there is a possibility that all data has not been extracted), the usual approach is to transcribe any original labels and discard the original file cover; there is no reason to treat digital media any differently.
- The media will fail with time, as will the devices needed to read them, and maintaining the necessary hardware to read old media involves all the disadvantages associated with technology preservation.
- Successful emulation is a better way of enabling the future researcher to experience the original environment.
