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Preservation policies define how to manage digital assets in a repository to avert the risk of content loss. They specify, amongst other things, data storage requirements, preservation actions, and responsibilities. A preservation policy specifies digital preservation goals to ensure that:
Over time all kinds of digital media become outdated. Technology is driven by innovation which unfortunately leads to very short periods of relevancy before redundancy. Data stored on redundant media becomes effectively useless if the appropriate hardware is not available to read it. This is a particularly difficult issue to manage where data is stored over long periods of time. Ideally, long term data storage should be technology independent, however this is not practical. A Cornell University website (mentioned above in another post) has actually documented the lifespan of various storage media with floppy disks lasting a whopping five years.
As hardware becomes redundant, so do file formats and the software which interprets them. A good example of this is Word Perfect; try to find a computer today which can read a Word Perfect document properly. Fortunately, system and format redundancy does not usually happen at quite as rapid a pace as hardware.
This is a massive threat to long term digital storage of any kind. Technology is so dynamic not only in innovations but also movement with vendors and competition killing off what seemed to be at one point very strong tech players. For this reason it would be a folly to rely too heavily on any one vendor/system/sponsoring organization because they change and often change quickly. Digital assets which need to be preserved long term must be protected from the failure of any one organisation. Unfortunately this is easily said but hard to plan for in such a dynamic environment.
Why Traditional Storage Systems Don't Help Us Save Stuff Forever?
Baker, M. Keeton, K. Martin, S. June 27 2005
HP Labratories Palo Alto
Basically no matter how much money you spend on the system housing your data there are still many ways in which it can fall over and create opportunities for data to be lost. This may be from hardware/software failure or an act of war. The longer you try to store data the more likely this will occur.
Some data can be related, and this relationship can be vital to data interpretation. A good example of this might be the Rosetta Stone, discovered in Rashid, Egypt. The stone is engraved with hieroglyphics in three different languages and without the "key" of what these symbols meant noone was able to read the inscription. It took a French scholar Jean François Champollion fourteen years to decipher the inscription. Can you imagine if you had to take that amount of time to decipher each document on your PC because someone had forgotten to preserve the relationship between that document and its key? It would be like trying to assemble Ikea furniture without instructions, a complete waste of time. Unfortunately, if this relationship is not identified and preserved when information is first stored it is unlikely to ever be recovered. The longer the data is kept without this relationship, the less likely it is to ever be resolved.
Sometimes people accidentally delete things and if it's the only copy, then it's gone. On the other hand sometimes people think that they no longer need a piece of data and delete it on purpose only to find that it was in fact useful. The longer you try to store data the more likely this will occur.
Unfortunately in the world we live in there are some people who intentionally destroy or damage digital assets for a variety of reasons. As much of the information is currently located in open access repositories accessible via the internet it is also vulnerable to attack. This is a threat to both long and short term storage.
No affordable digital storage is completely reliable over a long period of time. For example some CD's have recently been shown to have a life span of only 2 years which could cause significant problems for anyone relying on them. Other media such as magnetic tape also suffers various types of bit rot. The worse thing about this threat is that is often undetected until it's too late to recover the material. You would very nearly have to employ someone to check all your media all the time to minimise data losses which would make most of these mediums too expensive to seriously consider in a preservation project. Bit rot is inevitable with any storage medium over a period of time.
Many institutions simply do not have the resources, usually financial, to consider digital preservation. These strategies are often overlooked as low priority and are likely to remain so until a major data loss scares people into action.
And always make sure that Mr. Bean won't get access to your valuable assets!
http://www.records.nsw.gov.au/recordkeeping/topics/digital-recordkeeping/digital-records-preservation-discussion-paper/approaches-to-digital-records-preservation
In the encapsulation approach, records are packaged as bitstream with metadata enabling a user in the future to display them. The leading example of this approach is the Victorian Electronic Records Strategy (VERS), the digital preservation program of ADRI member the Public Record Office Victoria.
In the VERS approach, record content is accepted in formats including Text files, PDF, PDF-A, JPEG, TIFF and MPEG, encapsulated using an XML 'wrapper' containing a standard set of metadata elements and authenticated using a digital signature. Each record that is 'encapsulated' can contain multiple documents that together form a record.
Bitstream preservation can be used as a foundation for other preservation strategies but is not adequate on its own for ensuring long term accessibility and authenticity. It involves simply storing the binary code (1s and 0s) that comprises a digital object bearing in mind that the object will not be reproducible without the original combination of hardware and software that created it. The advantages of carrying out bitstream preservation include:
Is not suitable as a preservation strategy on its own.
Can be 'records-centric' - not as effective for recording contextual information about people, organisations and functions.
Content and contextual information kept together to minimise risk of loss.
Having the opportunity to go back to the 'original' record in this form to carry out different preservation techniques in the future.
Digital repositories are computer systems that ingest, store, manage, preserve, and provide access to digital content for the long-term. This requires them to go beyond simple file or bitstream preservation. They must focus on preserving the information and not just the current file-based representation of this information. It is the actual information content of a document, data-set, or sound or video recording that should be preserved, not the Microsoft Word file, the Excel spreadsheet, or the QuickTime movie. The latter represent the information content in a specific file format that will become obsolete in the future.
The Metadata Encoding and Transmission Standard (METS) is a metadata standard for encoding descriptive, administrative, and structural metadata regarding objects within a digital library, expressed using the XML schema language of the World Wide Web Consortium. The standard is maintained in the Network Development and MARC Standards Office of the Library of Congress, and is being developed as an initiative of the Digital Library Federation.
This approach involves preserving the bitstream of the record and developing a tool which will be capable of reproducing the intellectual content of the record in a different format. The tool must be developed before the record becomes obsolete. Migration is then only performed when a record is requested.
Emulation is the replicating of functionality of an obsolete system. According to van der Hoeven, "Emulation does not focus on the digital object, but on the hard- and software environment in which the object is rendered. It aims at (re)creating the environment in which the digital object was originally created.". Examples are having the ability to replicate or imitate another operating system. Examples include emulating an Atari 2600 on a Windows system or emulating WordPerfect 1.0 on a Macintosh. Emulators may be built for applications, operating systems, or hardware platforms. Emulation has been a popular strategy for retaining the functionality of old video game systems, such as with the MAME project. The feasibility of emulation as a catch-all solution has been debated in the academic community.
Converting to a different format may cause the record to lose authenticity if essential characteristics are affected.
Still relatively untested in digital records preservation.
Has the potential to be more effective for preservation of databases and multimedia.