code: public Constraint getModel(final Element element) throws IdNotFoundException {
  		Attribute attr = element.getAttribute(XMLTags.ID);
  		if (attr == null) {
  			throw new IdNotFoundException(null);
  		}
  		Constraint c = null;
  		final String id = attr.getValue();
  		try {
  			c = getModel(id);
  		} catch (IdNotFoundException e) {
  			LOG.debug("DummyConstraint fuer id " + id);
  		}
  		if (c == null) {
  			c = new DummyConstraint();
  			putToCache(id, c);
  		}
  		return c;
  	}
docs: Returns the constraint to the associated id attribute value of the passed element. To achieve
  this the id attribute of the passed element is searched first. If there is none an
  IdNotFoundException will be thrown. Then the constraint stored under the respective key is
  returned from the internal table. If this constraint is not found a wrapper is written to the
  table at the requested key. This way the sequence of the constraints in the XML file does not
  determine the cross-references by id. The wrapper will be replaced, if a constraint already
  represented by the wrapper in the table is generated later on.