code: public Collection<String> getKeysForType(Class<? extends XAttribute> type) {
  		Collection<XAttribute> typeCollection = getAttributesForType(type);
  		Set<String> keySet = new HashSet<String>();
  		for(XAttribute attribute : typeCollection) {
  			keySet.add(attribute.getKey());
  		}
  		return Collections.unmodifiableCollection(keySet);
  	}
docs: /* (non-Javadoc)
  @see org.deckfour.xes.summary.XAttributeInfo#getKeysForType(org.deckfour.xes.model.XAttribute.Type)