When an organisation is deciding on a preservation strategy, it will need to consider quality, convenience and cost of different approaches.
A common misconception is that applying migration as preservation strategy is less expensive than emulation on a per object basis. Usually not factored into the equation is that an emulator such as Dioscuri tackles multiple formats at once, and does so for the foreseeable future. Migration will continually need to be carried out to update objects to current versions. A comparison of long-term costs is depicted in figure 1 . This figure shows the actual project costs of developing Dioscuri compared with estimated migration costs required for retaining access to ten million digital objects (each object about 1 megabyte in size) over a period of twenty-five years. The calculated costs for preserving a single digital object of that size in the KB's e-Depot is about EUR 0.015 per year. This includes expenses for storage and server capacity but excludes personnel costs, training, housing, etc.
Applying migration to ten million objects once every twenty-five years, costs five million Euros. The actual expenses for emulation by further developing and maintaining Dioscuri costs about 600K euro. Taking into account maintenance costs of 20K euro a year, both preservation strategies become break even after five years; after that emulation becomes the more cost-effective solution. Developing new emulators - only needs to be done once per target platform.
This needs to be done once per emulator for each new generation of host platforms - the results could be shared between institutions. This can be complex as we have seen recently with the upgrade of GRATE to Ubuntu - there can be many dependencies that need to be dealt with. The use of virtualisation may help here - choosing an emulator which runs on a virtual machine means that only the virtual machine needs to be ported to each new platform, and all software for the virtual machine should continue to be available. That is the principle behind the UVC - but other more mainstream virtualisation approaches may also be helpful here.
Several institutions could share the cost of managing a software archive.
The PLANETS suite has a web services interface. In the future different network communication standards may be in place and the way that a platform like GRATE communicates with other systems will need to be updated.
To link each object to a technical environment that can be used to view it - and ensuring that all the components of that technical environment are available to the emulation platform.
[planetssuite:1] Hoeven, van der, J.R., Lohman, B., Verdegem, R., Requirements for applying emulation as a preservation strategy, IS&T Archiving Conference 2008, Bern, Switzerland, 2008. In: Archiving 2008, final program and proceedings, Bern, Switzerland, 2008.