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DigiCULT
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19
online in New Zealand, with a growth rate
upwards of 1 Terabyte annually.
11
Coupled
with the increasing quantity of offline
digital material coming into the Library,
the urgency becomes even greater.
Within the schema, preservation metadata
applies to a single `logical object'.This is an
arbitrary construct allowing the Library to
differentiate between:
- simple objects - one file intended to be
viewed as one logical object (e.g. a Word
document comprising one essay);
- complex objects - a group of dependent
files intended to be viewed as a single
logical object (e.g. a Website or a data-
base that is created as more than one file;
- object groups - a group of files not
dependent on each other in the manner
of a complex file, e.g. a floppy disk
containing 100 letters.This object may
be broken up into (described as) 100
single objects or four discrete objects
containing 25 letters each or it may be
kept together as a single logical object
(Joe Blogg's Letters).
This logical object is the Preservation
Master. Preservation metadata is held
against the Preservation Master. In practice,
this means that various other manifesta-
tions, e.g. dissemination formats, are not
considered preservation objects and will
not have preservation metadata retained
about them. Similarly, the schema acknow-
ledges that not all data key to preservation
processes will necessarily be held as preser-
vation metadata, e.g. data relating to rights
management and archiving permissions
will be recorded within a collection
management system and drawn on from
that source as and when required.
Preservation Masters themselves will be
subject to further preservation processes,
e.g. migration from an obsolete to a
current format.This creates a life cycle of
creation, use and eventual replacement of
Preservation Masters. At any point in time
there can only be one Preservation Master
and any object carrying that status will be
subject to the maximum preservation effort
of the Library's work are now available
3
following a process of peer review by a
number of international organisations
engaged in similar activities.
Work on the schema was initially informed
by other international endeavours relating
to preservation metadata, particularly that
undertaken by the National Library of
Australia
4
. Initiatives through the
CEDARS programme
5
, OCLC/RLG
activities
6
and the emerging consensus
regarding the role of the OAIS Reference
Model
7
(which was given an interesting
critique from an archival perspective by
Hans Hofman of the National Archives of
the Netherlands in Issue 2 of the
DigiCULT Newsletter)
8
, were also taken
into account.
In these initiatives there is a constant
tension between discussions of principles
relating to the conceptual nature of
preservation in the context of a Digital
Archive and the practicalities of ensuring
that the information necessary to describe
the digital objects contained in the Digital
Archive is captured.This is reflected in a
recent OCLC/RLG document which
emphasises `that these elements are not
necessarily atomic; it is easy to imagine
cases where the needs and characteristics
of particular digital archiving systems may
require deconstruction of these elements
into still more precise components'.
9
The Library's Preservation Metadata
schema is designed to strike a balance
between the principles of preservation
metadata, as expressed through the OAIS
Information Model, and the practicalities
of implementing a working set of preser-
vation metadata.The same incentive
informs a recent OCLC/RLG report on
the OAIS model
10
.
The schema proposed is not meant to
be comprehensive. Indeed, it is unlikely
that anything resembling a comprehensive
schema will become available in the short
term. However, the need is pressing.
Conservative estimates suggest that by
2005 there could be 12 Terabytes of
unique, digital original material available
while it has that status. A history of
changes made to the preservation meta-
data is also retained.This acknowledges
that the record is itself an important body
of data and processes about the object that
requires management over time.
The development of the preservation
metadata schema is one component of an
ongoing programme of activities needed
to ensure the incorporation of digital
material into the Library's core business
processes with a view to the long-term
accessibility of those resources.The goal of
the programme is to develop holistic end-
to-end processes for the handling of digi-
tal material within the Library.The
Library's approach to this is predicated on
the belief that dealing with digital material
will be essentially a `business as usual'
exercise notwithstanding the extra
complexities that arise from these objects.
3National Library of New Zealand. 2000. Metadata
Standards Framework for National Library of New
Zealand. http://www.natlib.govt.nz/en/whatsnew/
4initiatives.html#meta
4National Library of Australia. 1999. Preservation
Metadata for Digital Collections Discussion Draft.
http://www.nla.gov.au/preserve/pmeta.html. Accessed
11 May 2002.
5Cedars: CURL exemplars in digital archives. 2002.
Cedars guide to: Preservation metadata.
http://www.leeds.ac.uk/cedars/guideto/metadata/
guidetometadata.pdf . Accessed 11 May 2002.
6OCLC/RLG Preservation Metadata Working Group.
http://www.oclc.org/research/pmwg/.
7Consultative Committee for Space Data Systems. 2001.
Reference model for an Open Archival Information
System (OAIS).
http://www.ccsds.org/documents/pdf/CCSDS-650.0-
R-2.pdf
8Hofman, Hans. Review: Some comments on preserva-
tion metadata and the OAIS model. DigiCULT.Info: A
Newsletter on Digital Culture, Issue 2, October 2002, p
15-20. http://www.digicult.info/pages/publications.php
9OCLC/RLG Working Group on Preservation
Metadata. 2002. A Recommendation for Preservation
Description Information. http://www.oclc.org/rese-
arch/pmwg/pres_desc_info.pdf. Accessed 11 May 2002.
10OCLC/RLG Working Group on Preservation
Metadata. 2002. Preservation Metadata and the OAIS
Information Model: A Metadata Framework to Support
the Preservation of Digital Objects.
http://www.oclc.org/research/pmwg/pm_framework.pdf
11Extrapolations from: Lyman, P. & Varian, H. 2000. How
much information? Berkeley, CA: University of
California, Berkeley. http://www.sims.berkeley.edu/rese-
arch/projects/how-much-info/. Last accessed 17
October 2002.