code: public static boolean checkRegExp(String identifier, String datatype)
      {
      	Datatype dt = getDatatype(datatype);
      	return Pattern.compile(dt.getPattern()).matcher(identifier).find();
      }
docs: Checks if the identifier given follows the regular expression
  of its data type (also provided).
  
  @param identifier internal identifier used by the data type
  @param datatype name, synonym or URI of a data type
  @return "true" if the identifier follows the regular expression, "false" otherwise
  
  @throws IllegalArgumentException when datatype not found