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

[Sebastian Trüg]

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?

> 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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