Re-send to list, since I am not sure the first got through
Answer to mail sent 21 Aug
Best Regards, Eld
Fra: Eld Zierau [mailto:[log in to unmask]]
Sendt: 12. oktober 2012 15:54
Til: [log in to unmask]; Peter McKinney
Cc: Eld Zierau
Emne: Re: preservationLevelType -- request to PREMIS EC
Hi Pete, Angela and others
Firstly, I am very sorry for my late answer, I will be quicker next time!
As discussed in Toronto last week, the preservation level type is only proposed as an extra field in order to be able to qualify the aspect of a preservation level that the value is for. At the Royal Library of Denmark the preservation level type will relate to the strategy of preservation we use to achieve a specific preservation level. I have tried to give a more thorough description below.
It was never the intention to suggest specific values for neither preservation level nor the preservation level types. I think there is still no common understanding of what preservation level means in practice. And I think that your example Pete (together with mine) clearly shows that it would be very useful for both of our interpretations of preservation levels,
- but also that the values we would use are very different.
And as a follow up to Toronto, I also think that this shows that this introduces no restrictions to anyone - an optional PreservationLevelType field is only meant as a help to express the complex concept of preservation levels in a simple way.
Best Regards, Eld
Explanation of what we do at the Royal Library of Denmark
There are preservation levels for both bit preservation and functional preservation as explained below:
On the Functional Preservation Level (i.e. preservation that ensures that the bits remain understandable and usable according to preservation purpose) there are one type:
- PreservationLevelType= FunctionalPreservationStrategy: covering strategies like emulation or migration (at this stage we have 4 possible strategies)
On the bit preservation level (i.e. preservation that ensures that the bit-streams remain intact and readable) there are several types to cover different dimensions of bit preservation like integrity, confidentiality and accessibility (in accordance to the paper "Evaluation of Bit Preservation Strategies" from iPres 2010 and inspired by the ISO 27000 series):
- PreservationLevelType=BitSafety for bit integrity
- PreservationLevelType=Confidentiality for confidentiality
- PreservationLevelType= Accessibility for accessibility (Not implemented yet) Along with these types we will use different values indicating the level for each of the types - in my first mail I indicated 3 levels, but we actually end up with seven levels.
As example of how the complexity is expressed in a simpler way is that the above levels in combination covers 4*7*7*7=1372 possible preservation levels. As a start we have identified 8 of these in practical use, but where the number is very likely to be expanded and is far more readable by level types than by a list that suits the requirement at a certain point in time.