borghoff.jpg Notes from Borghoff et al. General intro to the field. Defines long term as “over 50 years.” In principle, bitstreams can be kept indefinitely. But the bitstream is inaccessible without an adequate rendition system, and this is what causes the problems. Often only the creating app can render the stream, but the app is itself dependent on a specific hardware/OS combination. A rendition system is a complex organism comprising the hardware layer, the OS and driver programs, and the presentation layer. Changes in one component prompts changes in the others.

Character sets like ASCII seem to be pretty long-lived.

Advantages of migration include:

  • ICT people know it and use it themselves, so there’s lots of experience
  • migrated docments are available on the current system, by definition
  • it satisfies the contemporary user’s needs and expectations.

Disadvantages of migration:

  • it often results in minor adjustments to the document, reducing authenticity
  • it cannot usually be automated, so it needs checking. [AA: is this true? Xena software?]

Advantages of emulation:

  • high authenticity
  • should result in relatively small costs per document

Disadvantages of emulation:

  • you have to have the HW spec, this is crucial. And the complete SW bitstream. And all the manuals, too. [AA: hope they are clearly written!]
  • emulators are complicated things to write
  • there may be SW licensing and copyright costs.

Other bits in this chapter which interested me:

  • Changing documents to a restricted set of standard formats is a possibility, but you will lose some information, just as you would when converting from one WP format to another. On the other hand, the costs of digital preservation are proportionate to the number of formats involved, so the fewer the formats the better.
  • Because metadata is useful for document retrieval, it should ideally be stored separately from the document itself. The MD should be stored in a simple character set like ASCII. [AA: or even on paper?] The very minimum MD set should be (a) author, title, date etc, (b) subject area and keywords for retrieval, (c) location of the document, (d) encoding and data format, (e) migration history and description of the original environment, (f) legal and access issues.