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

[Christian Mollekopf]

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());

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
> > > > > _______________________________________________
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