[Nepomuk] Re: How to detect new/removed tags from a Soprano::Statement?

[Christian Mollekopf]

On Tuesday 22 February 2011 11:28:35 Sebastian Trüg wrote:
> Hi Chris,
> 
> On 02/19/2011 01:39 PM, Christian Mollekopf wrote:
> > On Saturday 19 February 2011 13:02:20 Vishesh Handa wrote:
> >> The method Laura described is the correct one as of now. Though, we
> >> would prefer it if you didn't use it. The reason is that you get
> >> notified for all the statements that have been added/removed - and
> >> those can be quite a lot.
> >> 
> >> Especially if files or emails are being indexed. That causes the entire
> >> system to slow down. I had to monitor everything for Nepomuk
> >> synchronization, and it caused Nepomuk to slow down so much that in 4.6
> >> RC1, I finally had to disable it!
> >> 
> >> We are working on a better way for you to watch changes in the Nepomuk
> >> Repository. The current API that I have planned is something like this -
> >> 
> >> ResourceWatcher * watcher = SomeObject->watchType(
> >> Nepomuk::Vocabulary::NAO::Tag() );
> > 
> > what is SomeObject?
> > 
> >> watcher would have its own statementAdded() and statementRemoved()
> >> signals which would only give you those statements. I was even thinking
> >> of watching by property.
> > 
> > Yes, that would be good.
> > 
> >> Would this solve your use case? Any comments on the API? None of this
> >> has been implemented so feel free to comment - we can change anything
> >> at this point.
> > 
> > I have three usecases.
> > 
> > Usecase1:
> > Updating things like TagClouds where I need a signal when a new item of a
> > certain type (i.e. Tag) is added/removed to/from the repository. For this
> > the watchType with an added/removed signal for the concerned item would
> > solve my problems.
> > 
> > Usecase2:
> > I filter a QAbstractItemModel based on the PIMO:isRelated property.
> > So here I need a signal with the Resource and the changed isRelated
> > property.
> > 
> > Usecase3:
> > When I display an item in an editor where I show some Nepomuk properties,
> > I need a signal only for this exact resource.
> > 
> > I'd like a similar api like the akonadi::monitor:
> > 
> > 
> > 
> > //acts as a filter on the emitted signals for object type
> > ResourceWatcher::watchType(Nepomuk::Vocabulary::NAO::Tag(), bool enable =
> > true);
> > 
> > //If set emits only signals for the explicitly watched resources
> > ResourceWatcher::watchResource(const Nepomuk::Resource &, bool enable =
> > true);
> > 
> > //acts as a filter on the emitted signals for predicate
> > ResourceWatcher::watchProperty(Nepomuk::Vocabulary::PIMO::isRelated(),
> > bool enable = true);
> > 
> > Usecase1:
> > watcher->watchType(Nepomuk::Vocabulary::NAO::Tag() );
> > 
> > Usecase2:
> > watcher->watchType(Nepomuk::Vocabulary::NAO::Topic() );
> > watcher->watchProperty(Nepomuk::Vocabulary::PIMO::isRelated());
> 
> So here you want to be notified of changes that involve the properly
> pimo:isRelated and a subject of type pimo:Topic? In other words:
> whenever a property pimo:isRelated is added to or removed from a
> resource that has the type pimo:topic you want to be notified?
> 
Basically yes, although It would be possible to make the group of monitored 
resources smaller.

I have an akonadi model filled with items, and I filter those items based on the 
nepomuk topic. So I need to emit dataChanged for the correct item if the topic 
has changed, so the filter is reevaluated.
So I don't actually need to be notified for all resources in the storage but 
only a group of items. Maybe we could limit the resources by a custom mimetype 
or so?

So far I do not set any mimetype on the resources I create, but this might be 
something which should be done?

> > Usecase3:
> > watcher->watchResource(res, true);
> > //and maybe filtering for only the properties which im interested in
> > 
> > I think that would keep us quite flexible and would be exactly what I'm
> > looking for.
> > 
> > Cheers,
> > 
> > Chris
> > 
> >> On Fri, Feb 18, 2011 at 5:25 PM, Laura Dragan <aprilush at gmail.com> wrote:
> >>> On Thursday 17 February 2011 16:32:45 Christian Mollekopf wrote:
> >>>> Hey Laura,
> >>>> 
> >>>> On Thursday 17 February 2011 14:10:58 Laura Dragan wrote:
> >>>>> Hi Chris,
> >>>>> 
> >>>>> On Thursday 17 February 2011 01:14:02 Christian Mollekopf wrote:
> >>>>>> hi,
> >>>>>> 
> >>>>>> Does anybody know how I can detect when a new Tag was added/removed
> >>>>>> to/from Nepomuk? I.e. to update a Tag Cloud.
> >>>>> 
> >>>>> do you need to update the tag cloud if any resource is tagged outside
> >>> 
> >>> your
> >>> 
> >>>>> app, or just inside your app?
> >>>> 
> >>>> I'd like to update it whenever new tags are available, not only from
> >>> 
> >>> within my
> >>> 
> >>>> app.
> >>>> 
> >>>>> In SemNotes for instance the tag cloud is built only with the tags
> >>>>> used
> >>> 
> >>> on
> >>> 
> >>>>> the notes - you can find that code on gitorious.
> >>>>> 
> >>>>> A long time ago I wrote a plasmoid that built the tagcloud for the
> >>> 
> >>> entire
> >>> 
> >>>>> desktop (not sure if it's in playground or not), and that one was
> >>>>> listening to statementsAdded and statementsRemoved from the model,
> >>>>> but
> >>> 
> >>> I
> >>> 
> >>>>> took the easy path and rebuilt the cloud every time instead of just
> >>>>> updating it. It worked ok with up to 30 tags, without visible delays
> >>> 
> >>> from
> >>> 
> >>>>> all the repository querying.
> >>>>> 
> >>>>>> Currently I listen to the statementAdded/statementRemoved signals
> >>>>>> of
> >>> 
> >>> the
> >>> 
> >>>>>> Soprano::Model, and I can also detect if an Item gets a new Tag,
> >>>>>> but
> >>> 
> >>> I
> >>> 
> >>>>>> don't know how I can see from the Statement when a new Tag was
> >>> 
> >>> created
> >>> 
> >>>>>> or a Tag was deleted.
> >>>>> 
> >>>>> I think you can use the signals
> >>>>> 
> >>>>> void statementAdded( const Soprano::Statement &statement)
> >>>>> void statementRemoved( const Soprano::Statement &statement)
> >>>>> 
> >>>>> to look into the statements that are affected with the functions:
> >>>>> subject(), predicate() and object().
> >>>> 
> >>>> Thats what I'm trying to do, but I don't get what indicates that a tag
> >>>> is
> >>> 
> >>> new
> >>> 
> >>>> to the Nepomuk system (or that a tag was removed).
> >>> 
> >>> I'd do that by checking if the statement added or removed has the
> >>> predicate "rdf:type" and the object "nao:Tag". The subject of the
> >>> statement is then the uri of the tag that was created or deleted.
> >>> 
> >>> Laura
> >>> 
> >>>> Thanks for your help,
> >>>> 
> >>>> Chris
> >>>> 
> >>>>> Hope this helps
> >>>>> Laura
> >>>>> 
> >>>>>> Cheers,
> >>>>>> 
> >>>>>> Chris