Preservation of Digital Data by Christian Wellner Based on: Howard Besser. Digital longevity. In: Maxine Sitts (ed.) Handbook for Digital Projects: A Management Tool for Preservation and Access, 2000 Mary Baker et al.: A Fresh Look at the Reliability of Long-term Digital Storage. In: Proceedings of the 1st ACM SIGOPS/EuroSys European Conference on Computer Systems 2006.

Preservation of Digital Data Motivation Problems: Longevity, Visibility, Custody Proposed Strategies

Motivation Strong trend of digitalizing (historical) data  allows more efficient work  decreases storage space significantly  can be copied easily  Negative aspects are however often neglected

Problems of Digital Storage Longevity problems  Human „errors“ or catastrophes can still occur (burning a book vs. overwriting a file)  Durability of storage devices is physically limited („mutation“ of bits)

Problems of Digital Storage Visibility problems  Each storage device needs its special hardware (e.g. floppy drives)  Each file format needs its special software (e.g. word processors)  Manual decryption of binary code is (in most cases) almost impossible

Problems of Digital Storage Visibility problems  Files may be compressed (e.g. JPEG)  Companies aim to protect their own formats (e.g. with elaborate encoding)  data may only be readable in a certain context (e.g. on websites)

Problems of Digital Storage Custodial problems  Who is responsible to keep data accessible for future generations?  Regular analysis of the data is required to find latent errors, leading to monetary costs  restrictrions by copyright laws (especially if a third party owns the context)

Proposed Strategies Improving longevity  Using the safest hardware available  Constantly checking the data for latent errors  Protect the data against hacking or catastrophes

Proposed Strategies Key strategy: Redundant duplicates  „Refreshing“: a copy of the data that is to be preserved is made regularily  The data itself is only lost if all copies are lost  Important: storing copies in independant places

Proposed Strategies Two general options for visibility  Migration: files are translated into newer formats that can be directly accessed  Emulation: programs simulate the usage of the processor of the original format  Better standardization can also help a lot

Proposed Strategies Solving custodial problems  May require some changes in law  Allow website owners to preserve third party content if it is needed to display the site  Transfer responsibility to preserve it if data changes its owner

Proposed Strategies Meta Data  Can be incredibly useful to decipher a file  Directly shows how to handle the data  But does not give away protected information  Can be applied to any format

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