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[protege-dev] [protege-discussion] Problem with events and database backing

Timothy Redmond tredmond at
Sat Feb 15 09:39:14 PST 2014

I am a bit confused getting this message because I think that the new 
lists are protege-users and protege-dev.  So I am forwarded this message 
to protege-dev just in case.

On 02/15/2014 07:23 AM, clemens utschig wrote:
> folks - this is rather urgent...
> I try to get the listener magic to work (e.g. new instance created, 
> frame update, browser text changed) - between the protege application 
> and and multiple api based consumers all using the same - database 
> backed - project.
> It seems somehow events / listeners are not firing / generated by 
> default?
> Any help much appreciated.

This is just a thought and may not be related to what you are 
experiencing.  I am assuming that you are talking about Protege 3 
although -- even though the implementations are completely different -- 
the same comments apply to Protege 4 and 5.

If you create two separate Protege knowledge bases (e.g. separate java 
objects) that point to the same database then you will have several 
problems.  These problems only occur when modifying the knowledge bases; 
I think that things will work if all the callers are in read-only mode.

The most obvious problem is that changes in one Protege knowledge base 
will only generate events in that knowledge base and not in the other 
knowledge bases.  A less obvious problem is that, in certain 
circumstances, changes made with one knowledge base will not be seen in 
other knowledge bases.  There may be other problems as well.

If this is in fact your problem then there are two obvious fixes to the 
problem.  If everything is happening in a single JVM, then it is 
possible that you can refactor your code so that all callers requesting 
a knowledge base will get the same one.  Maybe there would be a static 
method or something that manages the process of getting the knowledge 
base.  Since the code will no longer be reentrant, you may need to also 
add some synchronization.

If you have more than one JVM or there is some other reason why the 
above solution is not practical then the other approach is to use a 
Protege server.  If you have several clients accessing the same server 
all the events and other synchronization will be taken care of.  This is 
easier than it sounds and there is a wiki page telling you how to do this:

      Protege 3       --
      Protege 4 and 5 --

The protege 4 and 5 versions use the OWL api and I suspect that we may 
not completely support them yet.


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