Page 67 - Building Digital Libraries

CHAPTER 4

safe as long as data backups are being completed. As the above illustrates,
this just simply isn’t true. Unless access and active evaluation are parts of a
preservation plan and process, an organization isn’t really doing long-term
preservation planning, but rather, just backing up bits.

Preserving the Content and Context,
Not the Medium

Preserving digital objects is significantly different from doing so in the ana-
log world. One major difference between digital and analog preservation
is that digital preservation should not be tied to a digital object’s physical
medium or carrier. Some cultural heritage organizations spend significant
resources attempting to preserve the physical media that digital objects are
stored on—tape drives, floppy disks, CDs, DVDs, flash drives, memory
cards, and other media. But this process is a fool’s errand because these
media eventually become obsolete and fail. These physical media may have
value as historical artifacts, but they have little preservation value. Digi-
tal data begins to degrade from the moment it is written onto a physical
medium, and it continues to degrade with each subsequent reading. Physi-
cal media will become less relevant as a growing number of resources are
transmitted over networks, though they will continue to play a role for the
foreseeable future. This means that organizations must be clear about what
they are trying to preserve and begin to plan on how that preservation will
take place.
Digital preservation focuses primarily on digital content and the digital
representation of that content. For example, let’s say that you create a doodle
in GIMP and save the content as a PNG (Portable Network Graphics)
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format and store this item in a digital preservation system. What are you
trying to preserve? Do you want to preserve the content, forever, as a PNG
and preserve just the raw bits for some later user to attempt to decode? Do
you want to retain the original compatibility with GIMP? Should you be
concerned with the representation of the data, that is, preserve the visual
display of the doodle so that it renders the same in fifty years as it does
today? These are all questions that archivists and digital library designers
are asking themselves every day, and this is why so much work is being done
in the areas of software emulation and migration.

Software Emulation
Software emulation approaches digital preservation as a bit-
level problem. Organizations seek to preserve the original, true
format of a digital object. In the above example, there is the
PNG-formatted file of my doodle. The system would then seek
to preserve the PNG format in perpetuity. The challenge with
this approach is that file formats change, they become depre-
cated, or unsupported, and they disappear. And this happens

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