Digital Preservation Policies: Technical Considerations

SAA Boston: 08-06-2004Andrea Goethals, FCLA

3 SuggestionsConsider your preservation policy a work in

progress. Version and date your preservation policy.

Separate the more volatile components of your preservation policy from the more stable components.

Keep in mind the fact that computers can be time-savers. Automate, Automate, Automate.

SOME of the technical considerations

See your handout for the list…Focus for today: file format decisions

File Format =A usually-documented way a single file

structures digital content and possibly metadata about that content.

File content := (internal metadata) * (content)+

3 File Format Examples

TIFF 6.0 XML 1.0 PLAIN TEXT

File Format Decisions in Policy

Which file formats to use for 'preservation copies’ (not access copies)

might digitize material to this formatmight convert other digital formats to this formatmight create a copy of other digital formats in this format

Requires value judgments on which formats make good preservation formats

You know a file format is a good preservation format

when …It accurately represents the real-world

representation Passes the Fidelity Test

It should be easy to interpret/copy/present/distribute in the future

Passes the Future Test

The Fidelity TestDepends on the original ‘input’

Requirements of oral history vs. a symphony performance

The Future TestSingle (free?) publicly-avail. spec. from a reliable sourceShort clear specificationSimple formatIncludes technical metadata needed to interpret the contentAvoids codecs, etc. that require license fees, etc.Relatively long history of use, well-supportedCompletely self-sufficient, no external file dependenciesDoesn’t lose info during a copy-to this formatNot dependent on the original ‘input’

Fidelity Test != Future TestA format that fails the “Fidelity Test” can ace the “Future Test”.

In the future you can perfectly support a poor representation of the input. (Bad)

A format that aces the “Fidelity Test” can fail the “Future Test”.In the future you can't support a faithful representation of the input.

(Bad)A format that aces the “Fidelity Test” can ace the “Future Test”.

In the future you can perfectly support a faithful representation of the input. (Good)

Tiff 6.0 takes the Future Test

Single (free?) publicly-avail. spec. from a reliable source: Yes, freely available from Adobe's website

Short clear specification: Yes: 121 well-written pagesSimple format: YesIncludes technical metadata needed to interpret the

content: Yes, Image File Header and one or more Image File Directories

Avoids codecs, etc. that require license fees, etc. : Maybe, if you avoid certain codecs (ex: LZW in TIFF)

Tiff 6.0 takes the Future Test

Relatively long history of use, well-supported: Yes, since Summer 1992, good support

Completely self-sufficient, no external file dependencies: Yes

Doesn’t lose info during a copy-to this format: Yes if you avoid lossy compression (ex: JPEG in TIFF)

RESULT: Tiff 6.0 aces the Future Test as long as the codecs used in the Tiffs are restricted.

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