AbstractPetriNetElementModel source = getQualanalysisService()
.getSourcePlaces().iterator().next();
AbstractPetriNetElementModel sink = getQualanalysisService()
.getSinkPlaces().iterator().next();
if (tStar == null)
tStar = new TStar(editor);
tStar.updateTStar(source, sink);
} else {
if (tStar != null)
tStar.updateTStar(null, null);
}