[Nepomuk] Data stored in database - how to manage, backup and merge?

[Karl Günter Wünsch]

Hello,
I have searched all available resources but haven't found a single comprehensive explanation on how to manage, backup or (most importantly for my setup) merge the data stored in Nepomuk. There is a lot of talk about how this data is improving your experience, as of yet my experience has been that setting up Nepomuk is a pain, the data is stored in a database of which there now are two disfunctional versions (redland and sesame2) and a new emerging functional one (virtuoso) and the data is not portable. 
It could well be of merit putting this information into a cloud storage eventually - but there is no such thing yet, so my questions are:
- How can you selectively remove entries from the database?
- How do you prevent entries from being deleted that may become relevant again (for example tag data for images that are only available on a temporary resource like an external disk)
- How do you backup your semantic data? Databases can become corrupt - I wouldn't want to tag thousands of images only to loose all this valuable information in an incident with the database.
- How do you merge two databases? - I have several computers and they all have shared access to my images, so sometimes I tag them using my main workstation but on trips I might decide to tag them using the notebook I have with me, the relevant information is now contained in two different databases which eventually require synchronisation! The same will happen with my Mail data and the adressbook for example now that Akonadi uses Nepomuk as storage.
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regards
Karl Günter Wünsch