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https://issues.apache.org/jira/browse/UIMA-360?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503429
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Jörn Kottmann commented on UIMA-360:
------------------------------------

I need a change notification layer for the cas editor.  The different parts of 
the ui (editor, outline view, properties view, etc.) only know the model (CAS) 
and how to display it, if the model is changed the views must be updated. The 
problem is that the views do not know each other, so they need change 
notification to know how the model has changed e.g. annotation was 
removed/added, annotation span was adjusted, etc.

I am not sure why do say this is a performance problem. A client would 
implement a listener interface and adds/registers
an instance of it. Then the uima code calls the listener if a change occurred. 
Sure this slows the uima code a little bit, but the key point is that it only 
slows the code if there are registered listeners. 
If there are no registered listeners the code is as fast as without change 
notifications.

> Add CAS change notifications
> ----------------------------
>
>                 Key: UIMA-360
>                 URL: https://issues.apache.org/jira/browse/UIMA-360
>             Project: UIMA
>          Issue Type: New Feature
>          Components: Core Java Framework
>            Reporter: Jörn Kottmann
>         Attachments: cas editor doc.txt, images.zip
>
>
> Add a facility to listen to changes which are made to the CAS.

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