Conceptualización e Importancia 31

about the potential for the essential link between object and record to be disrupted over long periods of time. Managers should assess the risks they operate with and decide which approach is more suitable

Quality control. Ensuring the trustworthiness of metadata records is a high priority.

Quality control measures are needed whenever metadata records are created or changed

Protection. The integrity of metadata records must be ensured, requiring the same preservation attention as the objects they describe.

14.19 Preparing the archival package for storage

Once the digital material has been transferred and any necessary control and description work undertaken, it must be prepared for entry into a storage system, ensuring the various part of the information package (including the content and any metadata) are linked, and a data stream created that can be safely stored on the storage media in use and can found by the appropriate file searching programmes. The package is then saved to storage. Before putting the digital object in storage as a preservation master, many programmes create additional copies, for at least two very good reasons:

In order to have a copy available for use without the need to extract the preservation master from storage. Use copies are often optimised for access with currently available communications and display technologies, (such as low resolution, compressed versions of image files that can be much more quickly delivered online). Derivative access copies generally do not need to be preserved across changes in technology, and they often do not have detailed preservation metadata records.

In order to store objects in more than one format, opening up alternative strategies for providing access in the future. As discussed in chapter 16, it is good practice to retain copies of digital objects in their original formats, regardless of the need to create new formats as a preservation master or current access copy. Obviously, any parallel versions must be managed as separate but related digital objects.

S PECIAL CONSIDERATIONS

Content information, consisting mainly of details about the technical nature of the object which tells the system how to re-present the data as specific data types and formats. As access technologies change, this re-presentation metadata also needs to be updated

Preservation description information, consisting of other information needed for longterm management and use of the object, including identifiers and bibliographic details, information on ownership and rights, provenance, history, context including relationships to other objects, and validation information, Obviously, some of this metadata may refer to other information objects such as software tools and format specifications that must also be managed. The interdependent nature of digital materials means that programmes often have to manage networks of linked objects and their metadata. There are still no accepted standards for preservation metadata schemas for universal use, so programmes may have to choose between accepting (and possibly adapting) one of a number of models being used by others, or designing their own schema (either as a complete solution or as a minimal interim one until a standard emerges). Many national archives authorities have released metadata specifications for record keeping systems that include preservation needs. In the library field, an international working group convened by OCLC and the Research Libraries Group (RLG) released a recommended preservation metadata framework in mid-2002 (available online at

<http://www.oclc.org/research/pmwg/pm_framework.pdf>). Their report is a good starting point for exploring the metadata that may be needed.

An interesting implementation by the National Library of New Zealand attempts to adapt the OLCLC/RLG work to a particular programme and its circumstances (available online at

<http://www.natlib.govt.nz/files/4initiatives_metaschema.pdf>). This schema proposes the following elements (somewhat summarised here):

Describing a digital object Name of the object

Local identifiers

Global persistent identifier File location in storage system

Date when created as preservation master Overarching technical composition (no of files of each MIME type)

Structural type (eg text, image)

Hardware required for object to function Software required for object to function Special installation instructions

Built-in access inhibitors and facilitators Quirks (in-built anomalies)

Authentication or validation keys Who created metadata and when Describing any process applied to an object (including creation)

Name of process Purpose

Agent who carried out process

Agent who approved process and when Hardware used

Software used

Steps involved in process Outcomes Standards or specifications used When completed

Describing technical characteristics of any files within the object

Specific file identifiers

Relationship to other component files File size

When created

MIME type/format (eg image/tif) Version

Key file that provides access Characteristics of specific file types

(eg for image files: resolution, dimensions, tonal resolution, colour space, colour management, colour lookup table, orientation, compression)

(eg for text files: compression, character set, associated DTD for structured text, structural divisions) (eg for audio: resolution, duration, bit rate, compression, encapsulation, track number and type) (eg for video: frame dimensions, duration, frame rate, compression, encoding structure, sound) (eg for datasets: common elements above only) (eg for executable files: common elements above only)

Describing update of metadata Agent modifying metadata When modified

Field modified

F OR PRESERVATION PROGRAMMES WITH FEW RESOURCES

14.21 Transfer

Programmes with few resources may need to explore ways of reducing transfer costs:

„Push” arrangements may require less investment by the preservation programme and shift most of the cost of transfer to the producer. However, without agreements about the media, formats and quality control to be used by producers when transferring material, short-term savings may produce greater preservation costs in the long short-term

Well chosen restrictions on the range of media and formats accepted by the programme may produce savings

programmes may be able to store transferred material on their transfer media if relatively stable carriers have been chosen, and if backup copies can be made for security. Some communities without access to separate preservation agencies may have to pursue a „non-transfer‟ model, setting up the best preservation arrangements they can within an operating environment. Even in these circumstances, many of the same principles apply: ongoing accessibility is more likely with some kind of internal transfer to even a modest „back up archive‟ where files can be managed outside the normal risks of operational use. Files will still need to be sufficiently well described and protected to allow later transfer to a more secure preservation programme.

14.22 Metadata

The costs of recording metadata can be a significant part of overall preservation costs. There may be potential for savings by either reducing the amount of information recorded to a minimum (and accepting that both access and preservation will be made more difficult); or by investing in software that will capture metadata automatically (which will become easier as

metadata standards develop). In choosing a minimal set of metadata, programme managers may find it helpful to consider what users will need in order to find material, and what questions will require answers in taking any foreseeable preservation action.

C ASE STUDIES