code: private ImmutableFunctionalTerm getTermTypeAtom(String string, Object type, String joinCond) {
  
  		if (type.equals(R2RMLVocabulary.iri)) {
  
  			return getURIFunction(string, joinCond);
  
  		} else if (type.equals(R2RMLVocabulary.blankNode)) {
  
  			return getTypedFunction(string, 2, joinCond);
  
  		} else if (type.equals(R2RMLVocabulary.literal)) {
  
  			return getTypedFunction(trim(string), 3, joinCond);
  		}
  		return null;
  	}
docs: get a typed atom of a specific type
  
  @param type
  - iri, blanknode or literal
  @param string
  - the atom as string
  @return the contructed Function atom