Long-term preservation
Data which are not archived or managed in a systematic way are in danger of becoming effectively lost. The passage of time increases this risk, and so active long-term preservation is needed.
As part of your data management planning, you hopefully will have identified the period of retention for which the data remain valuable: length of the project only, 5, 10, 20 years or indefinitely. This decision can be revisited after the data are in use. New uses for the data may come to light, or a historical value may be anticipated.
Fragility of data
Digital data - made up of bits and bytes - are in many ways more fragile than paper records for a number of reasons. Depending on the type of media on which the data are stored (magnetic, optical, and so forth), over time they are subject to different forms of 'bit rot' or decay, in which the electrical charge representing a bit disperses.
This gradually introduces either minor or major errors in the data, and their ability to be read by computer software.
Strategies
- Refreshment - move data files onto new storage media well within the projected lifespan of the media.
- Replication - by keeping more than one copy of a data file, the risk of losing a readable copy over time is reduced.
These strategies apply to both online and offline storage media. Where data are kept on a server, backup procedures and disaster recovery planning may take into account the necessary procedures. Ask your system administrator about their procedures and tests.
Offline storage media include optical discs such as compact discs (CDs) and digital video discs (DVDs). Depending on the quality, these may need to be refreshed every ten years or less. Portable flash drives can be useful for short-term backup and portability but are not reliable for preservation purposes.
Software obsolescence
Another threat to long-term accessibility of datasets is software obsolescence. When a new version of a software product is unable to render a file created in an older version, or when a software company retires a product, goes bankrupt, etc, there may be no available version of the software to be used on newer operating system platforms.
Strategies
- Migration - when a new software version has become established, the data file is converted or 'migrated' to the new software version or package.
- Emulation - a specialised strategy to recreate the functionality of the obsolete software package on a new operating system, or, for example, on a Java Virtual Machine system.
- Format conversion - the most pro-active method is to select a format that is most easily imported into a number of suitable software programs, or that is based on a universal standard.
Preservation planning
As most of the activity described above needs to be done at some future point(s) in time, planning for preservation is usually deemed to be essential.
The Open Archival Information Standard Reference Model (OAIS), originally developed by space scientists, is the pre-eminent model for preservation planning and is an International Standards Organisation (ISO) standard.
The Digital Curation Lifecycle Model is useful for mapping planned preservation and curation activities onto a lifecycle view of a digital object.
Two online books produced in the UK - Preservation Management of Digital Materials: The Handbook, by the Digital Preservation Coalition and the Curation Reference Manual (formerly the Digital Curation Manual) by the Digital Curation Centre (DCC) are excellent sources of detailed information for those tasked with long-term preservation.
Data archives and repositories
Services may exist that could relieve you as a researcher of taking on long-term preservation of data yourself.
Digital preservation and data curation are represented by emerging professional fields that are increasingly specialised. Specialists are knowledgeable about preservation planning and procedures, as well as standards, informatics, and discipline-specific knowledge and norms.
A big advantage of depositing your data in an archive or repository is that it will be preserved - even for your own future use!
This article was published on Apr 23, 2012