[Nepomuk] Re: same nepomuk db for several users

[Markus Leuthold]

On Monday, December 06, 2010 04:24:33 pm you wrote:
> Hi!
> 
> On Sun, Dec 5, 2010 at 10:24 PM, Markus Leuthold <nepomuk at titlis.org> wrote:
> > > On 12/02/2010 01:24 AM, Markus Leuthold wrote:
> > > > Hello list
> > > > 
> > > > We share our computer among several persons, each with a separate
> > > > user account. We want to have a shared nepomuk database. What's the
> > > > best way to do this? Creating a symlink of ~/.kde/share/apps/nepomuk
> > > > to a shared folder?
> > > > 
> > > > best regards
> > > > Kusi
> > > 
> > > This is tricky. It could be hacked with links indeed. But then no two
> > > users could ever be logged in at the same time.
> > > Why do you want to share the database?
> > > 
> > > Cheers,
> > > Sebastian
> > 
> > There are many possible use-cases for sharing tags. Some real-world
> > examples:
> > 
> > - me and my girlfriend are planning our vacation. She's tagging
> > documents, pictures etc with the tag "vacation-2010". In my account, I'd
> > like to see now
> > what is already available when I'm organizing our vacations in my
> > account.
> 
> In today's world, wouldn't your girl-friend and you have separate
> computers? I'm just saying that I think it would a lot-lot easier for us
> to work towards metadata sharing, rather than focusing on having a common
> Nepomuk db.

yes, we're having several computers. There's one centralized computer which 
has all the shares. A notebook automatically mounts the shared directory with 
autofs. 

> 
> - we're preparing a playlist for a party. We'd like to set the tag "party-
> 
> > playlist" in dolphin, running in each one's account. Since we're in a
> > hurry,
> > we're tagging the music at the same time on two different computers. So
> > it should be possible to have the nepomuk db on a remote location.
> > 
> > Having another Nepomuk db would be a very tedious job. I think it would
> > be
> 
> a lot simpler just for each person to have their own their Nepomuk db (
> like it is right now ), and additionally have metadata sharing. That way
> you can easily query all the music that has been tagged by 'person'.
> 
> I generally prefer peer-to-peer networks instead of a situation where there
> is a central database. In your case, what if the remote location isn't
> available at that point? With a de-centralized system, you can easily share
> or sync the metadata at a later point.

how does the synchronization of two databases work? A user doesn't want to 
manually trigger a synchronization. If the synchronziation of 2 databases is 
easier than keeping one shared db, then I'm all fine with it. I'm a bit afraid 
of a sync service running every 15min

> 
> > As mentioned later in this thread, not all tags should be shared. It
> > would be
> > nice to have several nepomuk-dbs (private/shared). I understand that it's
> > quite tricky to get the sharing right: It doesn't make sense to share
> > tags for
> > object which are not shared.
> > You could say that tags of files which are readable by both accounts
> > should also be saved in a shared nepomuk-db. Probably best would be an
> > extended user
> > interface where the user can choose the nepomuk location.
> 
> Having several databases would mean switching databases, and a lot of other
> ugly stuff like - which database should the indexed data be stored?

for writing, the user has to choose. it's like in a calendar application when 
you have several calendar files.

querying data from several virtuoso instances is indeed an issue, that's 
probably complicated to implement and doesn't scale well.


> What
> about the case where there is data common to both the databases? 
> We would
> need another virtuoso instance running ie more memory consumption.
> From the discussions we'd had at Akademy. I don't think getting sharing
> right is that complicated. We just haven't gotten the time to implement it!
> 
> > I'd like to mention that the workflow in digikam works excellent! We have
> > all
> > our photos in a shared directory. The sqlite3 file digikam4.db is
> > read/write
> > for all users, so each of us can tag photos (even concurrently) in
> > digikam in
> > our own accounts.
> 
> Could you elaborate on this? If you're doing it concurrently that means the
> database is stored in some kind of shared folder?

yes, the database is in a shared folder.

> 
> > Talking about concurrent access: are you sure 2 nepomuk clients cannot
> > access
> > the db at the same time? It works with digikam. You can have two running
> > instances of digikam (in two accounts), and when you change metadata
> > located
> > in digikam4.db, the change is immediately visible in the other running
> > instance of digikam
> 
> Digikam uses an sqllite database, we do not. There is an option for
> exporting the digikam data to Nepomuk, but internally digikam only uses
> sqllite.

nepomuk uses virtuoso as backend, which seems to be a regular database 
allowing multiple users to access the db. So it should be possible to share 
the same data among several users without any additional effort, the same way 
it already works with an sqlite db. Or where is the culprit?

cheers, Kusi