nsIRDFObserver Interface

 This method is called whenever a new assertion is made
 in the data source
 @param aDataSource the datasource that is issuing
   the notification.
 @param aSource the subject of the assertion
 @param aProperty the predicate of the assertion
 @param aTarget the object of the assertion

void onAssert(in nsIRDFDataSource aDataSource, in nsIRDFResource aSource, in nsIRDFResource aProperty, in nsIRDFNode aTarget)

 This method is called when a datasource is about to
 send several notifications at once. The observer can
 use this as a cue to optimize its behavior. The observer
 can expect the datasource to call endUpdateBatch() when
 the group of notifications has completed.
 @param aDataSource the datasource that is going to
   be issuing the notifications.

void onBeginUpdateBatch(in nsIRDFDataSource aDataSource)

 This method is called when the object of an assertion
 changes from one value to another.
 @param aDataSource the datasource that is issuing
   the notification.
 @param aSource the subject of the assertion
 @param aProperty the predicate of the assertion
 @param aOldTarget the old object of the assertion
 @param aNewTarget the new object of the assertion

void onChange(in nsIRDFDataSource aDataSource, in nsIRDFResource aSource, in nsIRDFResource aProperty, in nsIRDFNode aOldTarget, in nsIRDFNode aNewTarget)

 This method is called when a datasource has completed
 issuing a notification group.
 @param aDataSource the datasource that has finished
   issuing a group of notifications

void onEndUpdateBatch(in nsIRDFDataSource aDataSource)

 This method is called when the subject of an assertion
 changes from one value to another.
 @param aDataSource the datasource that is issuing
   the notification.
 @param aOldSource the old subject of the assertion
 @param aNewSource the new subject of the assertion
 @param aProperty the predicate of the assertion
 @param aTarget the object of the assertion

void onMove(in nsIRDFDataSource aDataSource, in nsIRDFResource aOldSource, in nsIRDFResource aNewSource, in nsIRDFResource aProperty, in nsIRDFNode aTarget)

 This method is called whenever an assertion is removed
 from the data source
 @param aDataSource the datasource that is issuing
   the notification.
 @param aSource the subject of the assertion
 @param aProperty the predicate of the assertion
 @param aTarget the object of the assertion

void onUnassert(in nsIRDFDataSource aDataSource, in nsIRDFResource aSource, in nsIRDFResource aProperty, in nsIRDFNode aTarget)